1992 Volvo 740 Wagon. Overdrive is not working, I check the fuse and it was blown. I replace the fuse and turn on the vehicle, everything is all good. I put the car in reverse and the fuse blows. The reverse lights and overdrive operate on the same 15amp fuse. I put in a 30 amp fuse and put it in reverse for a quick moment, reverse lights turn on. I kill the car and pulled the fuse, it was so hot I burned myself. I'm horrible with wiring and could only imagine this is a short, especially since there were tons of electrical issues I have already fixed, where should I start my search, or is there a way I can fix the issue easier than stock? I dont wish to bypass the overdrive because I occasionally haul a trailer. Thanks in advance!

 

sounds to me like the short is in the backup light circuit, not the OD circuit.

lets see, for the backup lights, ignition switched power goes to fuse 12, from there it goes through a connector A at the central electric unit to connector C at the manual gear shifter to the backup switch on the shifter assembly, then from that switch back through C, through A, then through connector B at the left A-post, and a black wire goes to the left backup light and on to the right backup light. Connector B is a big block 50-something pin beast of a connector behind/below the far left side of the dashboard, and the reverse light wire through it is black on pin 5.

is this car a stick or automatic ? With a stick shift, the reverse switch is in the transmission, with an automatic, its in the shifter assembly along with the park/neutral switch (and there is no connector C).

from the front of the car, the black wire goes to the back of the car in the driver side door sill, over the left rear wheel hump, and on back to the left tail light




SO... get yourself a bunch of 15A fuses before starting, *NEVER* put a bigger fuse in a circuit!!!!

I think I'd first unplug the harness connector from both tail lights, and put the car in reverse, see if the fuse blows.

if fuse did not blow, then the problem is a short in one of the tail light assemblies. plug in just the right taillight, put car in reverse, does fuse blow? then its the right tail light assembly, I'd remove from car and closely inspect it. if it doesn't blow, unplug the right and plug in the left, and again put car in reverse, if it now blows, its the left tail assembly, ditto remove and inspect for shorts. note, btw, the tail lights apparently use black for both ground and reverse, great fun.

if the fuse DID blow, its in the wiring harness or around the park/neutral sensor switch in the gear shift assembly. if you can find the connector A under the center console near or under the fuse/relay panel, it has a black wire on pin 1, and a blue-red wire on pin 2, unplug this connector, and it should disconnect the reverse lights entirely, see if the fuse blows now. Note unplugging "A" might disable the starter, as I think the park/neutral switch is on the same 4 pin connector (pin 3 is blue-green or blue, and pin 4 is white or pink.

 

[QUOTE=pierce;486147]sounds to me like the short is in the backup light circuit, not the OD circuit.

Thank you so much, I cannot look it over currently due to the fact my brother has borrowed the vehicle for work. It is an automatic (sadly) and if there is an issue in the taillight assemblies that would make sense. When I purchased the car the passenger side taillight assembly was doing all kinds of crazy stuff, so I jumped all the lights from the driver side except turn signals, cut the strip of ground that runs down all the lights at each bulb and ran a separate ground for each. I was going to start back there but wanted to get updated on the system as a whole before I began. In a few hours I will give it a look and will keep updated. Thanks again.