headlight switch function changes when car is running

[culp71]

I installed a restored dimmer and a new old stock headlight switch. both switches, are tight, and bench tested ok.
headlight switch (middle) up click and all dash lights come on along with outside running lights.
the dial dash dimmer functions like it should.
then if I put the headlight switch all the way up headlights come on, while running lights and dash lights stay on.
I tried this around 100 times in various order along with dome over ride opening doors etc, as I had to take dash apart and didn't have to do it again. all seemed fine.

I completed putting the dash all back together...everything worked the same so I turned everything off, put in key turned over engine and started it ,move headlight switch up to the middle function and nothing...and then I put it up into headlight switch all the way up, and the headlight and dash lights come on, but only once in a while.
I wiggled things but doesn't really seem to make a difference. if I put switch all the way up then ease it back closer to middle position everything comes on....but not always.

If I turn the engine off or turn key out of the run position the correct functions sometimes return, other times which is the most confusing is if I disconnect the battery then reconnect everything works fine.  until I turn over the engine or turn key into the run position... thoughts?

[Marc70challenger]

With most electrical issues - start with grounding.  Take a wire and temporarily ground the dash from a good contact point on the dash to good contact point on body. Try lights.  Could be a bad switch but I always start with ground issue.

[culp71]

thanks for the suggestion, that's what I first though as well, I now have three different grounds, none make a difference.
it is a new switch, but my old switch did the same thing but it was very loose, I thought it was a switch problem hence why I spent a bunch of money on a new OE headlight switch....only to have similar issue....

my main confusion is I can find nothing that changes in the electrical system when its not running compared to when it isnt...could it be an increase in power due to the alternator running that is somehow too much for these lights, or circuit, it doesn't blow any fuses, or even flicker like a bad connection, but should I put in a bigger amp fuse? I currently have a 10 in for the dash lights.

while this isn't going to prevent the maiden voyage, I was just really trying to have it all done when that occurs.

[Chryco Psycho]

I tend to agree , the lights are grounding through a cicuit that is not in use until the engine is running then the same circuit cannot be used as a ground , , is the dash frame well grounded ? It might be grounding through a tach wire through the coil 

[dodj]

It has been a few years since i messed with the headlights,  but isn't there a cct breaker within the switch? That may be the reason it 'resets' when you disconnect the battery.  It would also explain the erratic behavior of the switch while running. For some reason you have to much current going through the breaker.  If you had a dc clip on meter it could verify if you have a high current going through the sw.

[Cudajason]

I tend to agree , the lights are grounding through a cicuit that is not in use until the engine is running then the same circuit cannot be used as a ground , , is the dash frame well grounded ? It might be grounding through a tach wire through the coil 

Do you have the headlights properly grounded. 

Have you recently repainted the car and re connected the headlight ground...it could be bad due to the paint.

If the ground is loose it could be intermittent when the engine is running and causing the issue???

Jason