Doug1

My car is a 78 btw.
Let me say thank you to guys like DUB and SwampeastMike and some others who have posted a lot concerning electrical issues under the dash. So I have had an intermittent problem of no running lights and no dash lights. I can live without dash, but no running lights at night is a problem. I did't have any blown fuses, so it wasn't a short. I replaced my headlight switch thinking that was the problem, which it certainly can be with these issues. I also checked for resistance between the metal HS housing and ground, it was good, so I knew my headlight switch had good ground. I've heard that cleaning the ground that the HS is connected to is a real PITA, so I was happy about that.
The headlight switch gets two sources of power, one from starter that powers ONLY the headlights. Then there is a second source of power(which is a different terminal on plug) this is the orange wire. This powers the running lights and dash lights, dark green out of plug for dash and brown for running lights. That orange wire is connected to the fuse box on the RIGHT side, the one marked "tail"(second regular size fuse up from the bottom on left side of fuse box). DUB has talked about how these slots that hold the glass fuses can become corroded over time, now I will say, at least for me, that it wasn't very noticeable to the naked eye. So I pulled out the fuse and checked for resistance to the ORANGE wire going into the headlight switch, that is where my problem was, high resistance. So I ended up cleaning both sides of the fuse holders. I used a metal .380 bore cleaner for guns. After that a little WD 40 on q tips. Checked for resistance again, almost perfect. So then while down there I pulled out the small inst lps fuse and cleaned that. Put everything back together and everything seems good to go. My buzzer for headlights being on with no key started working again, nice and loud, it quit working a long time ago. It's light out, so I can't be certain on the dash lights just yet. But the running lights are definitely going strong.
Wanted to share what I've learned from all the guys on the this forum and some you tube stuff(how to test a GM headlight switch). Along with some schematics, I will give links. Thanks again, hope this can help some others.

Body wiring diagram
https://www.autozone.com/repairinfo/repairguide/repairGuideMain.jsp?pageId=0900c15280083 70b&source=pepperjam&affiliate_id=43737& click_id=2544396658&ppjmid=43737&cmpid=A FFS:EN:AZ:NL:1000000:GEN:ppjmid43737-8-11065#

How to test headlight switch, this is how I discovered the switch takes in 2 sources of power.

DUB

SUPER GLAD that you got this fixed and it was a somewhat simple fix and at least something you tested that I mentioned that I have encountered like I wrote in that other thread.

What may look good and seem to not be a problem often times when tested and checked can show a problem and needing to be cleaned like you did.

DUB

Doug1

Yes sir!
I went for a drive a little bit ago to my local autozone for a part, dash lights were very bright and running lights were fine. So nice to have things work the way they were meant to.
Thanks for the support.

Rescue Rogers

I had this same problem last fall and had to bypass the power to get the lights working again until I could get under the dash this winter. Thansk for the reminder to add this to my list and hopefully such and easy solution.

Doug1

Yeah, I was thinking about sending juice into the brown wire up front and see if that fired up the running lights. I was gonna tap into the headlight wire(I have a relay since I put LED lights in the grill as my headlights). I would have used a fuse inline at least. At 47 years old now, I try not to "fix" things like that anymore. I live in Florida and don't have a garage, so this time of year when it's cooler outside is when I don't mind messing with this kind of stuff. But I do hate getting up under the dash, it's very tight up under there with the seat and all. I have changed the seats from stock and getting them out is a pain too.

As a side note, I could be wrong, but I think the only reason the HS has to be grounded is for being able to turn the dome light on by turning the ***.

DUB

You are correct. It is the only circuit in the headlight switch that requires a ground to make it work.

DUB