I have the same issue with the dash lights and clock. All other lights work as they should but as soon as i pull the light switch out it blows the 3 amp fuse. Put a new light switch in but that has not solved the issue.
Frustrating.

 

There is a short in the wiring somewhere between the fuse panel and one of the dash lights or the clock. (I don't think the clock is on the same circuit as the dash lights, is it?) I had a similar problem with the taillights on the '73 Custom Cruiser I owned until a few years ago. As soon as I pulled out the headlight switch, the taillight fuse would blow. Had to meticulously trace the wiring, and the problem turned out to be a pinched wire behind the left side taillight. The car had been repainted, and when the shop remounted the taillights, they pinched a wire without realizing it.

 

The dash lighting wire is grey and is often mistaken for a ground wire. If you have an aftermarket radio/stereo it is not uncommon for the grey wire to be connected to something that it shouldn't be.

 

I moved your post to its own thread as your issue is not the same as the thread you posted your question in. As stated above your issue is a short in something that is powered off the gray wires only. Do you have a wiring diagram for your car?

 

Yes I have the big chassis book with all the diagrams in it.

 

You can easily follow the gray wires from the 3A fuse to all the lights in that circuit. That's where you need to look, I usually try to disconnect everything and then connect each wire until the fuse blows.

 

The frustrating thing is when people waste time and money replacing parts that can't possibly be part of the problem. The wiring diagram in your chassis service manual clearly shows that the 3A INST LPS fuse is DOWNSTREAM from the headlight switch. There is no physical way that the switch could cause that fuse to blow. The short is somewhere after the fuse. You will need to trace the grey wire circuit until you find the short. Has any work been done to the dash recently? Is it possible that the wire could have been pinched somewhere when parts were removed and replaced or components added to the dash? That's the first place to look.

 

OK- got to the back of the gauges and followed the grey wire. Unhooked the wiring connector on the gauge with all the idiot lights on it and lo and behold- all but 2 of the pins were broken off and gone! Guess that may be the issue with no dash lights and fuse blowing every time I turned on the head lights.

Started looking for a replacement gauge and not having much luck.
Any suggestions at this point other then installing aftermarket gauges under the dash?

 

I have replaced the pins with ( I believe) 2mm screws of the same length. There is a local Ace Hardware store that has drawers with small "hobby" screws.