First post, here we go. I have a 1972 Cutlass S, drive it as much as possible, enjoy it as much as possible.

Last time I drove it at night, everything worked fine. Tonight took it out and after the sun set, I noticed that my instrument lights were not working and checked the headlight switch with no luck. Got home and looked around the car and all running lights were not working either. Headlights, turn signals, break lights all work as well as the dome light, dash turn signal and bright light indicator. Just the running lights are out.

Checked the fuses and they are good.

I'm sure this isn't the first time this has come up and would appreciate any advice on where to start looking.

Thanks for any help.

 

The lights that are not functioning are all fed from the 20A TAIL fuse on the fuse panel. Don't just look at the fuse, use a test light to verify that you actually have power at the contacts on either side of the fuse itself. Sometimes the fuse can go bad and not show it, and sometimes corrosion can prevent current flow. After the fuse, a black with white stripe wire runs from there to the headlight switch. Verify that you have power where this wire enters the switch. Inside the switch the circuit splits. A brown wire comes out that feeds the park/tail lights. A separate conductor inside the switch feeds the dimmer rheostat, and from there a green wire leaves the switch and runs back to the fuse box where it powers the 4A INST LPS fuse before feeding the dash illumination circuit. Since the problem is common to both circuits, it has to be in the fuse contacts, wire from there to the headlight switch, or the switch itself.

 

Thanks Joe, I will start looking today. I was out there earlier and it also appears the after market tach back-lighting is out as well which makes sense since it turns on with the running lights. It's been in it for around 10 years without issue.

 

Yeah, they likely just spliced into the instrument illumination feed wire when that tach was installed (which would have been the correct way to do it) and if it's been working previously, you are correct that it is likely not the issue (however look for places where the non-stock wiring might have rubbed through and shorted over time).

 

Have you checked to see if the dimmer switch is turned down by chance?

 

That has nothing to do with the fact that his running lights are not working either. It would be prudent to start troubleshooting with items that are common to both the running lights and the dash lights.

 

My lights did the same in my 62 super 88. The dimmer was corroded inside, turned the **** back and forth and sprayed wd40 inside works fine now

 

I have checked the switch and am slowly narrowing it down to thinking it might be a bad switch. Also going to have fun taking out the seat today (not quite a flexible as I used to be) to get a better view under the dash. Will update soon. Thanks all!

 

I don't wish to throw a wrench into your troubleshooting procedure; yet, I don't want you to just toss a part at this and find out it wasn't the switch. Removing the switch is not fun, replacing the switch is not fun. IMO, I'd first perform the test(s) as Joe suggested (unless you really just want to spend the afternoon removing the switch if you have nothing else to do). Use a simple test light and ensure you have POWER on both sides of the FUSE and at each wire. Then, you'll know if it's worth the bother to R&R the switch. If you have no POWER on both sides of the fuse, then the switch isn't your issue.

 

In case you're unfamiliar with a simple test light. You can pick one up at any automotive parts store for generally <$10. Saves tons of time deciding if you do or you do not have power (the first order of business).