96 12v gauges read weird if headlights are on?

I’ve owned the truck almost ten years need to update my signature it’s got s362sxe/s475 compounds I installed (thanks power driven diesel). However an unrelated ground or harness issue has arised after a few months. When the headlights are on The engine temp gauge rises, volt drops and so does oil pressure, trans temp also rises. Knowing how each gauge works I’m assuming bad ground or connection but battery is new and connections are spotless with new Marine grade eyelets and tight nuts.

I guess the question is if there is a well known spot in the cab harness that wears through? I’m hoping someone has seen this issue and can help with a simple remedy.

Thanks

Pull the light switch out and check it, they're almost always melted. I'd start there.

jasonc said:

Pull the light switch out and check it, they're almost always melted. I'd start there.

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I’d also start there. I’ve replaced a few of these switches on 94-98 second gens. One guy literally had smoke come out of his dash from the switch shorting out.

Go ahead and buy or build a relay harness for the headlamps if you don't already have one. It will take the current load off the switch.
I would do this even if it isn't the root cause of your problem.

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Thanks, I have had a light switch catch on fire and smoke was coming out of the dash yrs ago. I will check it but I just noticed the gauges move when you turn blinker on also. I’ll do some digging when I get to the shop and I’ll post what i find.

Headlight depo sells a plug and play harness and relay kit if you go that route, your headlights will also be brighter.

Gasoline Sucks said:

Thanks, I have had a light switch catch on fire and smoke was coming out of the dash yrs ago.

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Just to be clear, was this the same truck with the funky oil/temp/etc issue, correct? I have replaced the headlight switch on my 1994 and 1998 2nd gen as well.

No I haven’t had any issues Aside from the headlight switch trying to burn it down. I ordered a set of LED headlights I think oil lanterns would be brighter then the stock ones.

I did some tests with the power probe and found the passenger battery ground wire that goes to the fender broke off the eyelet. Probably from wrestling the turbos in 10 times during mock-up. Put a new eyelet on and everything is back to normal. Thanks for the pointers!