Running lights on a 72 Caddy

[Reaper]

I know this could be an infinite problem when it comes to electrical, but the running lights, back side marker lights, and license plate lights are all not working. All the bulbs are fine as the turn signals, brake lights, and hazards all work. Even the fuses are all ok. I am thinking its a grounding issue back there but took the panels off the sides so I could get to the taillights but don't see any ground wire coming from it. Looks like the lights are all wired together, unless I am not seeing a different spot where the ground is. I even tried to take a piece of speaker wire and hook one end to a metal ground, and touch it to areas around the light assembly, but still no running lights.

I am hesitating taking it back to the mechanic as that could cost me dearly. The front side marker lights haven't worked correctly either. The turn signal bulb just stays lit while the other bulb does nothing. Seems to work that way on the drivers side, and not at all on the passenger side.

Any ideas on where the ground wire is supposed to be located? Chiltons doesn't help me out in locating the issues.

[Highbars]

The brake,turn,and hazard all use a different filament in the bulbs...so they could all work fine and you could still have bad bulbs..(dual filament bulbs) The are also fused separately so you should have separate fuses for tail,brake,turn.. it would be odd to have all these bulbs out at once but not impossible...The marker bulbs and license plate bulbs are probably 194's and not uncommon for them to be burnt..the stop and tail bulbs are 1157's and if over time you lost one tail light and didn't notice then the other..there in lies the possibility..Usually the rear lighting uses the same ground location... It will be in the rear either to the frame or near the bumper... You might be able to trace back from the license plate lite and find the wires...As a starting point I would use a 12volt test light and test for power in the tail lite socket with the bulb removed and test light hooked to good ground... Your turn signals work so with the key on and a turn signal on and running lites on you should one terminal in the socket that makes the lite flash and the other will just turn it on... If test light won't come on steady then you have lost power to socket on tail lite circuit.... If you don't have a test light just replace the bulbs and see if they work... the 194 bulbs will look dark and shiny like chrome if they are burnt ... Usually.. I hope this helps.... Lighting can be a bitch sometimes...

[Reaper]

Yeah I checked all the bulbs too because I wondered if that was the first problem. The dual filaments are all intact in each of the bulbs, and I even replaced the side marker bulbs even when the old ones were ok, but they still don't do anything. I will get myself a test light though and work on checking for the ground wire. Today I am going to JB weld the crack in the Y pipe on the exhaust so I can silence it. Thanks for giving me some things to check on.

*Update*
Not sure what was jostled around back there, but I did very little and all of a sudden after months of not coming on, the running lights back there are working. I tried moving the wires again to see if they would go off again but nothing happened. Not quite sure what it is, but if it happens again, I will know what the deal was and attack it head on in the same place. Just glad they are working. Now I have to figure out what the deal is with the front sidemarker lamps.

[hotroddwayne]

I had the same problem with the lighting on my '67... sometimes stuff worked, most of the time NOT. I found several factory "quick disconnects" under the car, along the frame that led to marker lights & turn signal/brake light filaments & they were corroded. Pulled them apart one by one, cleaned them out, & all my lighting works good now. Using a test light I got nothing @ the light sockets, but after pulling apart the quick disconnects under the coach & testing there... I had 12 volts. Trace your wiring back & test along the way to find where the problem is.

[Highbars]

It definitely sounds like a connection problem somewhere... did you move anything when working on y-pipe...? Great place for electrical problems in that area...Just don't let electrical problems get you all jammed up... Always start with the first step.. Checking Power and Grounds... Always Always Always......Will help in not getting on the wrong track right away.....

[Reaper]

Wouldn't you know it that they went off again and I shook connections, disconnected and reconnected them, but the running lights in the back never came back on.

As for checking, I have made sure all my glass fuses were good, and checked all power sources and found no issues. Now for grounding, that is where I run into a roadblock. I cannot find where the actual ground wire or grounding spot is in back or front of the car. I've seen the ground for headlights but no sidemarker or taillights. From what I saw on the sidemarker lights, the wires go directly into the firewall and into the fusebox. So I am not sure where these damn ground wires are supposed to be grounded at. Even tried taking some wire and ground it directly with no success. I'm at a loss and fear I will have to take it back to the mechanic again.