chasing a crazy electrical glitch?


Staff member
your simply wasting your time and money if you don,t own a few basic tools like a multi meter ,fuel pressure and vacuum gauge
and a trouble code scanner,

and a vehicle and year specific SHOP MANUAL!


set up a multi meter like this picture posted a bit lower in this thread, and pull fuses one at a time to locate shorted circuits
obviously the battery connections and cables need to be carefully checked and of course the alternator needs to be tested to verify its producing the voltage and current its designed to provide.
If your trying to locate a electrical drain causing the battery to go dead over a few days time, you could start by disconnect the ground or neg battery cable battery lead , put a digital volt meter between negative cable and battery post and measure current amp draw while , your using needle nose pliers and pulling fuses one by one to identify the circuit that has the electrical drain on it..
Need to duct tape over pass side door interior light switch so you can access fuse panel without interior light on, with that pass side door open to allow the access to the fuse panel.
There are also other items fed diectly off the battery ( through fusible links) that would have to be metered individually after removing wires from the post behind battery.
Headlight motors , heater control module , etc have hot feed ignition key off.
don,t try starting the car until the battery cable is replaced and cleaned as the starter load amps will cook a multi meter.


as usual you generally start the process by pulling the trouble codes , and looking up what they indicate in the factory shop manual,
many FLAKY problems in the cars electric system can be traced to bad grounds, loose connections, loose grounds, and pinched wires,blown fuses, on older cars corrosion is also a factor.
water that gets into the wiring can be a huge problem,wet, loose, or broken electrical connectors or corrosion on connectors, is also possibly a cause of intermittent problems
many times a V.O.M. meter can help isolate the cause.
think back, have you installed gauges, interior panels,installed body panels, rugs or interior components recently, just before the problem started, a screw in the wrong place, an overly tight bolt,or components pinching wires or grounds that were not re-tightened correctly can easily hit , pinch or cause problems with wires.
there's usually a REASON things started to go weird, and more times than most of us want to admit its something we did previously or failure to keep the car dry thats the source.
systems don,t have to be related to cause problems, a pinched wire can drain the battery over several days, your turn signals or interior lights might not work if an engine ground or ground to the dash electronics is loose, pull fuses,check grounds, get a darn factory shop manual, its MANDATORY WITH MOST OLDER PERFORMANCE CAR OWNERSHIP!
USE IT TOO isolate and correct those problems.
step one is getting a shop manual so you can easily trace the wires and colors, obviously if it blowing the fuze the indications point to a short or ground, being the cause,but a component that got wet or a wire that got pinched during an accident or during a repair is most likely, I generally remove the fuse and Ive got a test fuse I soldered two wire leads to that connect to a 9 volt battery powered buzzer, it plugs in where I removed the fuse and buzzes,unlike a light so you don,t need to keep looking at it, I then I go looking for loose or rusted connectors, pinched wires, loose grounds, etc. when you find one the buzzer either tends to get louder or stops
you might also keep in mind that some types of solid core ignition wire cause transient problems with computer controls due to electrical field interference

Here are some instructional,s and tutorials on how to use a VOM ... eruse2.php ... gindex.htm (early vettes gauge repair)


knowing whats going on and WHY can help,
reading links may not be fun but it will lead to the correct answers

but there are fairly fast and easy tests that will rapidly lead you too answers, and narrow down the cause of any problem, allowing you to isolate then correct the issue

think logically,what changed, the engine heated up and you had some fuel pressure flowing thru the engines fuel delivery system, if it starts up and runs but after its run, won,t re-start, its more than likely either a heat or sensor related problem or fuel pressure related issue, obviously a bit of testing helps isolate it.(pulling trouble codes tends to help locate this)
set and verify your ignition timing, pull trouble codes,set your tps and iac,, then check for vacuum leaks on the lines and intake,then get out your multi meter and verify all the sensors, chances are good its a defective heat sensor or defective o2 sensor, a logical step by step approach will lead you to the problem, youll be amazed at what youll learn reading links. use of a shop manual and multi meter can be very helpful
your working at a huge dis-advantage if you don,t have a factory shop manual for your specific year car, and basic tools like a multi-meter, and vacuum /pressure gauge

YOU may be amazed at the number of times a bad sensor or loose wire, bad ground or blown fuse is the problems cause.

I've seen guys rush out and spend hundreds of dollars on parts,too fix a problem, take a great amount of effort to tear apart the dash or other area and once the new parts installed it still won't work, so forced to do further research at that point they only then find a blown fuse or corroded electrical connection.(that was the true initial cause)

image_6238.jpg ... 98674.html





Grounds00021a.jpg ... index.html Location View 86.pdf ... Wiring.pdf


viewtopic.php?f=70&t=1443&p=3211#p3211 ... butor.html,11 ... lected.htm


posting.php?mode=edit&f=80&p=1025 ... 528008fdea

a spark checker can be useful

1.To do any logical trouble shooting on electrical issues you must have a good wiring diagram of the car.

2. remove all fuses.
3. place an amp meter in the positive battery line.
4. replace fuses one at a time.
(replace one record the current then remove the fuse, and proceed to the next fuse and circuit.)

5. now with this information you must isolate which circuits should have caused or continute to cause the electrical drain, and which should or are not a problem.
6. once identified and isolated the circuit can be examined isolated from others and fixed, with the shop manual, and A V.O.M. METER.

looking for a problem of this type is like looking for a needle in a hay stack unless you use a procedure like this and it will overwhelm you.

Last edited by a moderator:

If your getting a bright blue spark, with an audible snap when you pull off an ignition wire and hold it about a 1/2" from a good ground while the engines running I doubt your coils defective or needs replacing, but other components besides the coil can be a problem,


normally read ,
between 0.8 ohms-to-1.3 ohms between the positive and neg electrical connections, just the calibration on your multimeter, or test clips, can change this slightly so try to be aware of this.
10,000-13,000 ohms between either of the electrical connections and the coil to distributor wire connection terminal
and off the chart between the positive and neg electrical connections and the outer case ground.
if your experiencing an ignition problem .drop back to the basics and test your battery voltage, alternator out-put, all battery connections, frame grounds, and all ignition components like ignition wire resistance in OHMS and coils, rotors , caps and firing order,and ignition timing distributor end play and bearings,advance weights and springs, and in most of the modern engines the sensors also play a huge roll in ignition precision, things like temp sensors, crank position sensors, and maf sensors , knock sensors all effect the ignition, etc. you would be amazed at how often minor parts cause major issues

I figured Id point out a few basics
that I find it hard to believe are commonly over-looked
that's the fact that you'll want to
check the condition of the batteries and electrical connections in any meter you use.
before you go doing any testing.

I can remember several times that I've found
9 volt and AA batteries inside multi meters that were corroded and leaking acid,
and remember guys telling me injectors were defective, only to find later that the meter they used to test with was defective or the internal fuses or battery was dead, or 90% dead and
internal connections in the multi meter were corroded.
and as a result, connections internally were damaged so badly that the connections were turned to white metallic salts.
Ive also watched and seen guys try to check for good grounds , or ohms resistance or voltage and spend a lot of wasted time ,
because the multi-meter had a blown internal fuse , or the connector probes & leads, that did not fit,
and were not designed to be used with that particular multi-meter.

having a wide assortment of different multi meter test leads available is a huge benefit while testing
the clip test leads that test thru a wires insulation without much damage are a big help




having a set of needle bed test clips to check through insulation helps at times


most internal fuses will have the voltage/amps stamped on them,
any mechanic should have an assortment in his tool box, as your constantly going to need replacements while testing auto related issues



always make a point of flipping the multi meter too low range OHMS and touching the leads from common (BLACK) to (RED) test lead tips,
to watch the display or needle bounce to verify the multi meters functioning,
then place the black ground or common lead on a cars grounded chassis,
and touch the red probe to a fuse and verify it reads 12-14 volts current


useful related info

image_12926.jpg ... 98674.html
having a wide assortment of different multi meter test leads available is a huge benefit while testing
the clip test leads that test thru a wires insulation without much damage are a big help

















starter circuit, ignition timing or your alternator ,giving you trouble? read thru the sub linked info,

step one

clean the battery connections very carefully, and reconnect them tightly to the battery, once youve done that...verify youve got fuel pressure at the injectors and spark at the plugs
verify youve got 12-14 volts at the battery AFTER youve got the starter turning the engine over or at least trying to do so., do the interior lights get dimmer when it cranks over? does the voltage drop off?

step two

try starting the car while youve got it hooked up to a second car with battery cables or hooked up to a high amp battery charger there ANY differance?

step three
get your remote starter switch, bye-pass the ignition and see if the starter works without the ignition solinoid connections thru the ignition switch
Last edited by a moderator:

If the battery drains after running the car in what you may feel is far less time than might be normal, youll want to check all your frame grounds and then try to isolate the problems source, You disconnect one battery lead , put a volt/amp multi meter between the negative cable and battery post and measure current draw while pulling fuses one by one to identify the circuit that has the excessive drain while the cars not in use.
don,t forget you'll to Need to duct tape over any door , hood or trunk contact switch thats open while testing so you don,t find in error, its the interior lights circuit causing the problem,I know corvettes have contacts that turn on under the hood and rear hatch lights and youll need to do it so you can have the door open as you access the fuse panel without interior light on
There are also other items fed directly off the battery ( through fusible links) that would have to be metered individually after removing wires from the post behind battery.
Headlight motors some accessories,, heater control module , etc have hot feed ;key off.

THESE LINKS should help


viewtopic.php?f=55&t=1241&p=3037&hilit=+sensor#p3037 ... mation.htm


Measured Value
Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
Engine Oil Temperature Sensor. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.
Oil Pressure Sender/Switch. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.
Outside Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
In Car Temp Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
MAF (Mass Air Flow) Sensor. .4 Volts @ idle, 5 Volts @ Full Throttle.
Oxygen (O2) Sensor. .1 Volt Lean Mixture, .9 Volt Rich Mixture.
TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.

Sensor Locations


Engine Coolant Temperature Sensor. Front of engine, below Throttle Body.
Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter.
Oil Pressure Sender/Switch. Top, left hand rear of engine.
Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel.
MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear.
Outside Temperature Sensor. Right side of engine, top right corner of radiator.
In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid.
MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body.
Oxygen (O2) Sensor. Left side of engine, in exhaust pipe.
TPS (Throttle Position Sensor). Right side of throttle body at the front.
Well, I've ended up integrating some military training as a lifestyle. analytical troubleshooting, using the "Navy approved" seven step procedure. I found that it translates well to just about all aspects of "its broke, how do I fix it?"

I figured I'd share it with you guys, even toss in some of the explanation to the "cryptic" shortness of each line item.

1. Symptom recognition - this is basically realizing that something is wrong with a device or system. The more knowledge you have of the system or device the better you can recognize if its not operating correctly. i.e. calling tech support for them to fix your computer, but can't do anything they tell you to try until the power comes back on.

2. Symptom elaboration - varying the operating areas to see where the errors lie. like changing the channel on a TV to see if its just a channel bad, or if you completely lost the cable. seeing if the miss on idle stays there at higher RPM's that kind of thing.

3. list of probable faulty functions. in electronic work schematics are excellent to trace what COULD cause a fault where you find fault. Always list wiring and circuit board traces. (broken vacuum lines also) basically a function is something bigger than just a component, fuel system can be one, with components of pump rod, etc... though listing a fuel line would be a function as well.

4. Isolate faulty function - test areas to verify things are good at start and end of the function.

5. Isolate faulty component - pretty much what it says, once you find where the problem lies generally, move to the specific.

6. Repair and retest - fix or replace what broke, and see if it did the job. if you aren't infinitely knowledgeable of what you are working on, its possible that you found what broke, blew up, or worked fine, but missed a separate component that was causing the fault to appear in the component you just replaced. if you repair and retest and poof, pop, zing, or other not so happy sounds ensue, or it still doesn't work, then you have to go back to where you might have missed or overlooked something.

7. Failure analysis - This is one that in an official capacity is frequently required. in automotive work call it maintenance records. But for failure analysis, its looking over the systems to make sure you fixed what broke instead of fixing what was broken because something else had broke, and taken it out. basically its the paperwork version of a retest, or at least a way to look over system interactions to verify that how the part broke was at least addressed. it might be as simple as the part that was replaced needs or needed to be upgraded since it wasn't up to the load required of it, think of a small intake valve and a HUGE capacity manifold/fuel injection system. slightly flawed analogy, but it gets some of the point out there.

overall knowledge of the systems, ability to read/decipher schematics etc.. makes it more probable that you can find issues and solve them, sometimes without keeping tabs of progress on paperwork. The more experience, the more research, the more in depth you get in working on the stuff, the better you can get at finding where the issue lies, even if its just knowing that X supplier makes parts that are disposable out of the box, or should be disposed of, or that this fuel system setup will not work with THAT engine. I've found this forum, and the Chevytalk forum invaluable since there are people with a lot more information than I have, but know what question to ask..... usually.
grumpyvette said:
thanks for posting that's a useful list to use to get your mind on the process when basically trying to find out whats wrong

well, got it hammered in for Electronics tech, but wow it works excellent for any time something goes boink, pop, whistle, or just kablooey.
Bad plug wires?
Is there any way to check each wire other than to swap the whole set?"

thats what one of things the OHMS setting on your v.o.m. meter, can be used for, good copper core plug wire will read between 45-100 ohms per foot ,the ohms readings vary a great deal between manufacturers and different types of ignition wire so get a new section of similar wire about 2.5 feet long and use that to gauge a reasonable resistance reading on your meter, if your over 1500 ohms you've usually got a defective plug wire and don,t forget to visually check for loose connections and burn marks,and to check the coil and its connections and its wire to the distributor.
one old trick is to open your cars hood on a dark night or in a closed garage with low light conditions, and briefly start the engine while you, look for arcing while moving the ignition wires slightly.
try to use the type with a solid copper core if its an older muscle car without a computer or the carbon core with the spiral wrap wires shield if its computer controlled as the copper core style causes electrical fields that drives most car computer sensors nuts


BTW if your ignition, or any other electrical component is blowing fuses step one is getting a shop manual so you can easily trace the wires and colors, obviously if it blowing the fuse the indications point to a short or ground, being the cause,but a component that got wet or a wire that got pinched during an accident or during a repair is most likely, I generally remove the fuse and Ive got a test fuse I soldered two wire leads to that connect to a 9 volt battery powered buzzer, it plugs in where I removed the fuse and buzzes,unlike a light so you don,t need to keep looking at it, I then I go looking for loose or rusted connectors, pinched wires, loose grounds, etc. when you find one the buzzer either tends to get louder or stops

you simply take a blown fuse and solder the leads to the buzzer to the legs and insert it into the fuse box just during testing, but its a very good idea to put a inline fuse in the leads so you don,t have problems, obviously you don,t need more problems caused by testing

If your checking for a battery drain, or short in the cars wiring ,that leaves the battery dead over a few days ,disconnect the neg on battery and put a 12 volt light tester between the neg cable and battery, and shut interior lights off or just take bulb out, the light tester should not be lit with nothing on in the car, but if you have a short in the wiring it sometimes will. So then just remove 1 fuse at a time till test light shuts off, then you can narrow it down once you've located the offending circuit to what is draining your battery, if your like most guys you'll find it harder to keep looking up at a test light or meter than to wires a 9volt or 12 colt buzzer with two 5 ft long 12 ga wires and two alligator clips, this is frequently easier because current flow makes the buzzer sound so you know without looking up,from testing or pulling fuzes when the current thru the buzzer stops or starts during testing. ... Id=2102786


Last edited by a moderator:
get out your multi meter and set it to D C VOLTS 0-20
you need to logically isolate the problems source.
a lose electrical cable , or a defective starter or a connection or ignition switch may be suspect.


place the black common lead on the bat neg,POST NOT CABLE the red lead on the bat positive,POST NOT CABLE, it should read near 12-12.7 volts
now start or try to start the car if the voltage drops , the NEW battery may be defective, but its much more likely the battery cable connections too the battery or the ground cable may be faulty, now move both leads to the battery cables and repeat the test if the battery voltage drops noticeably more one or both cables are loose or defective, if your dome light dims as you stated when you try to start the car, chances are very good the battery cable or ground connections need to be carefully cleaned!
once the car starts it should have the alternator kick in and the meter should read near 13.9-14.7 volts at idle.
btw the most common electrically related problem I see on a consistent basis is corroded or badly rusted or defective battery connections and grounds so before you go crazy its a good idea to replace those as a first step in any electrical problem diagnoses
the threads have links youll need

as always you simply isolate and test in a logical manor to find the cause, random guessing and parts replacement without testing gets damn expensive and your unlikely to randomly guess correctly before it costs you more than it should to correct! ,Id start with having a local auto parts store load test the battery after getting the multi meter out you have , and cleaning all the cable connections carefully and ohms test them
and yes you need a multi meter and if the battery checks out Id be looking at the connections on the starter and the starter itself

one very common cause of ignition issues is burnt or arcing plug wires.and nu-shielded solid copper core ignition wire will cause electrical interference that makes some computers malfunction
many guys don,t take the time to carefully lay out the ignition wires in a way that prevents headers or exhaust manifold from damaging the wires, over time., and a, loose or burnt ignition wire will cause all kinds of engine problems.
one old trick is to open the cars hood in a dark garage or at night and look for electrical arcs as they are far easier to locate under poor light conditions, but careful inspection and use of a voltage/ohms meter will usually point out a bad wire quickly. as will careful testing with an infrared temp gun as a tool to locate missing cylinders. be sure to check the spark plug condition with visual inspection, and if your engines fuel injected check the fuel pressure and use a NOID LIGHT to see if your getting electrical pulses from the wiring harness.
personally Ive always preferred the 10.4 MM TAYLOR ignition wires








very tight access but at least is do-able

badly designed headers with limited access

related threads

viewtopic.php?f=70&t=840 ... 351?page=2 ... wires.html

viewtopic.php?f=50&t=3110 ... index.html ... 3_inst.pdf





Last edited by a moderator: