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Discussion Starter #1
When I purchased this '66 coupe for my son we found that the underdash harness had been hacked and spliced and shorted to the point that it was just junk. Surprisingly, even with the major short it had, most of it still worked. Except the 2.5 Amp circuit did not work and when the headlights came on the front parking lights went off.

So I replaced the underdash harness, the head light switch, and all the wiring under hood. The only original wiring is the wiper motor and the section that feeds the rear lights and fuel tank sender.

And guess what, the 2.5 amp section still does not work and the front parking lights still go off when the head lights come on!!!

How can this be? How can I replace almost everything and still have the same problem? What's left that did not get replaced should have no impact on the problem I'm having. I'm thinking the car must be possessed.

I did unplug the feed to the rear, and the wiper motor harness and I still have the same problem.

Where I'm at right now is: At the fuse box there is no power to the 2.5 amp fuse. What would the most likly place for an open be for this circuit?

Why woud the front parking lights go off when the headlights come on? There does not seem to be a short, it seems that the circuit for the parking lights goes open when the headlights come on. ??

I've gone over everthing so many times I know every connection by heart. Any and all ideas are welcome.

Thanks,
 

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Its normal for the parking lights to turn off when you turn the headlights on. Running lights didn't happen until the '68 model year IIRC. Hope this helps
 

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Discussion Starter #4
I never realized that. I've had my '66 Fastback for some four years now and I never knew that the parking lights went off when the headlights came on. /forums/images/icons/blush.gif

So you solved half of my problem... thanks.
 

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Discussion Starter #5
I thought it had to be the switch. The 2.5 amp circuit runs through it as to do the headlamps. But the new switch did not change a thing. The power feed to the 2.5 (this is the dash lights among other things) must be open, somehow, somewhere.
 

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Be warned, the advice i'm about to give is based on memories over 25 years old.

I had a 65 buick skylark that i rear ended sombody (dad was not happy). Well i did a bit of backyard body work on it trying to make it look a bit better. I had something bery similar to what you descibed happen. There was a ghost in the electrical system. It turned out there was a problem with the ground on the turn signals out by the turn signal itself. It had nothing to do with the wiring and switches under the dash. Fortunatly i was working on the fender and bumper and figured i had caused it and i retraced my steps.
 
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