Rear lights

[NJ C10 Guy]

I'm having an issue and just want an opinion on it. as of right now both of my brake lights work and my turn signals work. the passenger side rear running light sometimes works when I turn the headlights on, but it stopped working today when I was messing with the wiring and connections. The rear side marker lights aren't working and I'm not sure they have at all since I bought the truck. I tried to check the connectors and they seem ok.

Should I be looking at the wiring as the culprit? There are ground wires bolted to the rear of the frame, and the opposite ends are loose. I've tried putting them on bolts in the bed just to temporarily ground them but nothing has worked. I'm no electrical guru, but having ground wires bolted to the frame independent of anything else seems like it isn't doing anything. It would make more sense if the wires came out of the harness to me.

I also saw something somewhere about it possibly being an issue with the headlight switch?

Also, the brake lights will turn on with the truck turned off and the lights turned off. Checking the fuse box they are in the same slot as the hazard lights, so I'm assuming that's ok?

Thanks in advance for any help.

[IADC43]

Sounds like you are on the right track. Chances are, the side marker lights not working are a poor connection problem at the socket, or the supply wire from the Y. I'd make sure you have power to the socket with a test light, and check for continuity on the ground wire.

General suggestions for wiring problems:
Make sure you have good bulbs by testing them to light up.
Then, make sure the grounds are good and not corroded.
Then, test the supply wire. If there isn't power to the end where you want it, test it at a source you feel is good (firewall or at a junction). If you have power there, follow the line to find a break or corrosion.
Generally, it will be bulbs, connections (sockets or junctions), grounds, or bad wires.

[NJ C10 Guy]

I'll check that out. The lights looked good to me and not blown. I'm going to really clean the connections today. Could it be the fuse? Is the fuse for the tail lights the same as the dash lights? If so, that one is blown I found out, and could be my problem possibly. Also, the ground wire coming from the frame...should I connect that to the back of the tail light housing?

[NJ C10 Guy]

Update

So I cleaned off the connections as best I could as well as the grounds. Still have no tail lights, but the brake lights and the turn signals work in the rear. Here is an interesting twist: There is a 12V switch wired into my ashtray in the dash. When I turn that switch on, one of the reverse lights comes on. I tried to swap the bulbs to see if it was a bad bulb, but only the one side worked. Could there be an issue with the fact that the transmission was swapped from a column 3 speed to a 4 on the floor? I still have the original column in the truck for now, but i will be swapping to an automatic steering column in the very near future.

[NJ C10 Guy]

So I used my test light and discovered the following:

- turning on the 12v switch up front (previously mentioned), the back up lights worked no problem
- the turn signals/brake worked without issue as well
- still no power to the tail lights or the side markers, even making sure i had a good ground

I checked the lights at the sockets, the connectors at the bedside, and at the rear of the truck from the main harness running down from the bulkhead. The light green (back up) and brown (turn signal/brake) were the only ones that worked. Is there anywhere else I can check using my test light?

I am kinda stumped here. Could the issue be the fact that the old 3 speed column is still installed and the truck is now 4 on the floor? Also, silly question, but which fuse controls the rear lights? it should be the same as the headlights, correct? they work without issue so it wouldn't be the fuse.

[VetteVet]

Here is the wiring diagram for the 86. The first part is the front end and shows the fuse panel. The second part shows the rear lights and the brown wire is for the tail lights not the turn signals or brakes. Strangely the rear markers are not shown but they are wired directly in with the brown wire for the tail lights.

The third one is for the 88 and it shows the marker lights wired into the brown wire. They should be very similar.

[NJ C10 Guy]

I'm sorry it was light green and yellow that were working, not brown which is the wire for the tail light, side marker, and license plate light. The wires I have in the back are Lt Green (back up) brown (running/side marker/license plate) and yellow (brake/turn). I used this diagram as a reference:

http://forum.73-87chevytrucks.com/sm...?topic=11766.0

I am getting used to reading the diagrams, and i traced the brown wire (br 9) back to the "instrument panel 1" diagram. from where it connects with the rest of the rear lights, it appears to make a jump over and join the front lights. from there it appears to be connected to the front marker lights, and the front lower parking/turn signal lights. ill have to check tomorrow to see if they light up. i know the front signals work (light blue) on both the lower lamp and marker. i just dont know where to trace this back to in order to fix it.

[NJ C10 Guy]

turned out to be a fuse issue. i feel like a dummy, but at least it's all better!