Blowing Turn/Haz Fuse in Reverse Gear 86 C10 Scottsdale

[lotus1438]

Hello all, I'm a newbie around here. I just got a nice 86 C10 305 4BBL auto trans a few weeks ago. I've had some electrical issues. The first issue was the backup lights blowing a fuse immediately as soon as I put a new fuse in, this was resolved by unplugging the cig lighter The issue I'm having now is, the fuse blows to turn/haz as soon as I put it in reverse! How do I fix this? This makes the turn signals and the rear brake lights not work and is very annoying. I've heard this is caused by a faulty back up switch, I've heard turn signal switch too.  Again, I've never seen the back up lights come on. All other lights including side markers and dome light are working great. At some point some idiot also painted over the license plate lights and that area has cut wires, but I don't think it's related.  Please help and thanks in advance!

[hatzie]

Hello all, I'm a newbie around here. I just got a nice 86 C10 305 4BBL auto trans a few weeks ago. I've had some electrical issues. The first issue was the backup lights blowing a fuse immediately as soon as I put a new fuse in, this was resolved by unplugging the cig lighter The issue I'm having now is, the fuse blows to turn/haz as soon as I put it in reverse! How do I fix this? This makes the turn signals and the rear brake lights not work and is very annoying. I've heard this is caused by a faulty back up switch, I've heard turn signal switch too.  Again, I've never seen the back up lights come on. All other lights including side markers and dome light are working great. At some point some idiot also painted over the license plate lights and that area has cut wires, but I don't think it's related.  Please help and thanks in advance!

You have a short in the backup lamp circuit. Probbably between the column switch and the lamps.

My Droid from orbit

[gunrac]

likely cooked by exhaust

[lotus1438]

So where would that be? Between the column switch and the lamps exactly, sorry I'm just now trying to learn this stuff? There is a slight exhaust leak under the hood. Needs a new gasket, getting that fixed soon.  Also is it possible that it is the back up or turn signal switch?  Thanks.

[lotus1438]

Update. I'm not longer blowing a fuse when I put the truck in reverse. I didn't do anything but now my tail lights arent working, reverse lights never have. Brake lights still work though. Any ideas?

[hatzie]

Low probability that it's one of the switches.

A major possibility is some moolie from U-wreckit chopped up the tail harness with Scotchloks to "install" a trailer plug instead of just getting a Hopkins trailer lamp tap that plugs in between the tails and the harness.

The tails are actually just four wires exiting their own plug section of the firewall bulkhead plug assembly.  They immediately travel down to the RH frame rail and straight back to the tail lamp disconnect plug at the back of the RH frame rail. 
Parking/Running/license wire, Backup wire, LH turn/brake wire, and RH turn/brake wire.  The lamps ground to the bed sheet metal directly behind the lamp assemblies.

Examine the wires where they exit the bulkhead plug and run to the frame rail. 
Look this wire run over all the way back.  I have seen transmission crossmember and other bolts that were not carefully installed pinch this wire bundle.
Look over the short tail lamp harness that runs along the rear bed crossmember.  If you have to pull the lamps, remove the grounds and drop the tail lamps harness out of both sides to get a good look do it.

I have seen dual filament 1157 bulbs installed in the single filament 1156 sockets and vice versa...  I've also seen 1157 bulbs forcibly inserted backwards in the sockets.  Neither is a recipe for normal operation.

[lotus1438]

I did just get the transmission sealed, had to take it back and they resealed the deiveshaft yoke under warranty too. It's leakfree now but i think the brake lights were working fine before they worked on it.