Turn signal/hazzard/headlight issue

[92 Dime]

Got an electrical problem. '86 GMC 2wd. Found out today I had no rear lights: no turn sgnals, no brakelights. These went out about the time I turned the headlights on in a rain storm.

Checked fuses. None blown.

Checked bulbs. Two were burnt out, so replaced them all. No change.

Removed, cleaned, reinstalled ground connection on the rear frame. That got me a dim glow on the filaments. At one time there was a trailer connector splice in, but this was later cut to disconnect. I removed the electrical tape wrapping it all: water poured out. Got that drying now.

Tried the hazzard lights to see if that had any effect on the turn signals. They were subjectively a little dimmer. I think this was a mistake, as now when I try the turn signals, they function as hazzard lights. Left turn, right turn, doesn't matter: every light that can flash, does.

With the headlights on, I have no lights in the back.

Swapping out the flashers with known-good flashers had no effect on this.

Any recommendations on trouble-shooting from here? Pretty sure (but not certain) that rat's nest where the trailer connector was spliced in is involved. Should I start there?

Where are the grounds from the cab back? (Maybe a better way to put that would be "where should the grounds be from the cab back?")

Worst case scenario, if I splice in new wires from the cab back, any recommendations on wire gauge and number/location of new grounds?

thanks guys. I hate electrical problems.

[Palf70Step]

You may have some corrosion in your wiring harness causing a lot of resistance/even a short. I would be testing each lead at the terminal both at the firewall and at the end leads at the rear of the bed.

[Dead Parrot]

Double check the front of cab to engine ground cable. That is often misplaced during engine work. Often runs from a stud on the firewall to a passenger side valve cover bolt.

Yes, I would start with the "rat's nest" of trailer hookups.

IIRC - there should be a ground from each rear taillight to the body. Given where they are, spray from the rear tires often wet them and eventually corrosion does its thing.

[Axle]

I had to cut out the entire rear section of wiring on my '83 to just past the axle. Water had gotten into the wires and wicked up them, started as a simple fix turned into chasing back to clean copper.

[92 Dime]

Thanks guys! Still working on it. . . .

[92 Dime]

Probably a dumb question, but how long can I make the ground wires?

The truck is going to get a flatbed this fall/winter, so I'm thinking it might save some time to run the grounds to the frame instead of trying to find a good location on the body.

If I do this, should I increase the size of the wire?

[Palf70Step]

Length isn't important and yes I did mine to the frame also instead of just the body. Make sure all your grounding circuits are good. Battery to frame, grill support/cab to frame and engine to cab and frame

[hatzie]

The taillamp grounds are connected to a tab on the bedside behind the lamp housing.
You can extend em down to the frame using two ring terminals and a wire. No cutting and splicing.

U-wreckem and Ryder made botched messes out of the lamp wiring on many vehicles by tapping in with Scotchloks for trailer wiring. Scotchlok connectors are evil things that share a close kinship with Satan. They should both burn for eternity.

[92 Dime]

Originally Posted by hatzie

The taillamp grounds are connected to a tab on the bedside behind the lamp housing.
You can extend em down to the frame using two ring terminals and a wire. No cutting and splicing.

U-wreckem and Ryder made botched messes out of the lamp wiring on many vehicles by tapping in with Scotchloks for trailer wiring. Scotchlok connectors are evil things that share a close kinship with Satan. They should both burn for eternity.

Actually, I wasn't that lucky. The trailer connector rat's nest was done with 18 gauge red wire "spliced" in, and wrapped with elelctrical tape. . . cheap electrical tape. Then it was ripped out on an obstacle, and cobbled together. Then I bought the truck. . . .

Tab is rusted away on passenger side, am guessing the driver's side too. I'm going to solder in a length of 14 gauge wire on each side and take it down to the frame. Been cutting away the red wires and patching things back up. Now if I could only remember to put the heat shrink on before I solder!

thanks for your help guys--if the rain holds off a little longer, I'll be back with an update.

[hatzie]

86 uses a 2x2 four position Weatherpak at the frame. You can separate the lamp harness right there.
If you need to fix it near the connector you can put new terminals and seals on the wires and insert em back in the connector.
It's four wires.

I have a Mouser BOM Project I can probably share with all the parts for both halves of that connection.

[92 Dime]

Originally Posted by hatzie

86 uses a 2x2 four position Weatherpak at the frame. You can separate the lamp harness right there.
If you need to fix it near the connector you can put new terminals and seals on the wires and insert em back in the connector.
It's four wires.

I have a Mouser BOM Project I can probably share with all the parts for both halves of that connection.

Hatzie, I'm an idiot. What's a "Weatherpak", and what's a "Mouser BOM project"?

Got all the tape off where the trailer connection was, found the only black wire hanging in space. Spliced in an extension, heat-shrinked it, and got a ring terminal on and mounted to the frame.

Partial victory--I now have brake lights, even with the headlights on. Have full brightness on the turn signals, but if I use either, they both flash. Split the cover on the wires in the lamp harness to get to the tabs, turns out the connector is plastic--not connected to any wire.

I can, at this point, solder all the ground wires (1 for each of 3 lights) to a single ground wire, and take that to the frame. Any reason not to?



thanks,
Jim

[hatzie]

Mouser electronics allows you to share a bill of materials (BOM) I believe they call it a project... It'll have the full parts list so you don't have to chase all the little bits and pieces to order something like this. I've never shared one so don't count on it working for me.
Mouser stocks GM Delphi electronics (now Aptive) Weatherpak, Metripak, Packard, and many other automotive connectors and terminals.

Weatherpak connectors are a common Delphi electronics early weatherproof automotive connector. GM used these a lot in the 1980's and 1990's
Unlike the Metripak family the Weatherpak connector family is only one terminal size with one to twenty two male or female terminals in each connector half.
This is the square 2x2 4 position Weatherpak connector pair that should be in your taillamp wiring. There's a flat four terminal Weatherpak as well but that's not what GM used on the 83-91 CK & RV series taillamps.


No reason at all not to run the grounds directly to the frame.

[92 Dime]

Hatzie, thanks for the info. I found almost half of the weatherpak zip-tied to the frame. Argh. . . .

After a couple weeks of driving back roads to and from work, and getting rained out every time I had a chance to work on it, I got a couple days off. Took two hours today, tracing wires and splicing in new, replacing a couple of sockets and bulbs, etc. I now have working brake lights and rear turn signals--thanks to everyone for the help!

For future reference (just in case anyone has the same problem), I found that pulling the fuse for the brake lights/emergency flashers "fixed" the turn signals. I re-wired the brake lights from about 3' forward of the bumper, replaced the sockets, and did a solid ground to the frame on both sides.

[hatzie]

Originally Posted by 92 Dime

Hatzie, thanks for the info. I found almost half of the weatherpak zip-tied to the frame. Argh. . . .

After a couple weeks of driving back roads to and from work, and getting rained out every time I had a chance to work on it, I got a couple days off. Took two hours today, tracing wires and splicing in new, replacing a couple of sockets and bulbs, etc. I now have working brake lights and rear turn signals--thanks to everyone for the help!

For future reference (just in case anyone has the same problem), I found that pulling the fuse for the brake lights/emergency flashers "fixed" the turn signals. I re-wired the brake lights from about 3' forward of the bumper, replaced the sockets, and did a solid ground to the frame on both sides.

I haven't been able to figure out how to share the BOM on Mouser directly.
I've attached a ZIP archive with two duplicate spreadsheet exports of the Mouser BOM in XLS and ODS formats.
84-91 Square Taillamp BOM.zip