1998 Gmc Sonoma backup light

[Shannon Conner]

It is a 4 cylinder 5 speed. The backup switch works. When I put it in reverse, the fuse blows. It used to work. Then I replaced a bulb that was blown. I noticed the bulb I took out was not the correct bulb. I am wondering if the bulbs I have (which are the correct ones according to the numbers and Haynes book)are sucking to much juice and therefore shorting out the circuit. I followed the wires from the trans to the fuse box. No breaks or areas where there might be chaffing from what I can tell. Also I traced wires from fuse box to the rear where it stops at a plug. I was told the plug might be bad. I said I dont understand because it worked before AND there are no breaks, tears, chaffed marks, or burn marks in the bulb socket, or in the plug. I also used 30 amp fuse when only 25 is required. Still blows. Thank you in advance.

 

[Grumpy]

obviously youll need to use a automotive 12 volt dc bulb designed to fit the socket your using.

if its blowing the fuse the chances are EXCELLENT that the sockets defective or internally grounded,
the sockets are generally cheap & easy too replace
ID start testing trucks wire/socket,test the socket, by cutting off the power feed wire, at the socket and replacing the fuse , leaving the power supply wire open, Id suggest you use a multi meter and check continuity too ground,(with the switch power off) now replace the socket, check the ground contact to earth/frame ground continuity, (should be good) then check the power contact to ground, the contact should not show continuity, only 12 volts, once the switch is thrown to on, the bulb is the connection between the sockets contacts.
without the bulb inserted the power on should not blow fuses, with the switch off insert the bulb, now switch it on, the light should light but the fuse should not blow.

http://garage.grumpysperformance.com/index.php?threads/multi-meters.3110/#post-71867

http://garage.grumpysperformance.co...-auto-elecrtrical-connectors.3105/#post-68805

http://garage.grumpysperformance.com/index.php?threads/chasing-a-crazy-electrical-glitch.986/