1971 Coupe 350 w/air and 400 automatic. I decided to hook up a battery and test the lights before I install the driver side dash panel. All went well except I had no gauge lights....at all, none anywhere. First thing, check the 5 amp fuse, it was blown, so I went on a scavenger hunt for the correct size fuse, I found one in a variety pack at Auto Zone. I decided to use some other fuses that I have a bunch of instead of sacrificing the only correct fuse I have, they fit perfectly in the clips of the blown fuse. So I decided to check the operation of the switch without the dash light circuit in play. As I operated the switch in and out I noticed that the running lights would go off and on when they shouldn't, indicating a probable dirty or corroded switch internally. I dismantled the switch and found nothing real bad, so I went ahead and used some electronics cleaner to remove the 50 year old lithium grease, then went over all the contact surfaces with 600 emory cloth, hit it with another shot of cleaner and blew it all out with compressed air. I reassembled it and hooked it up to the wiring harness. The running and headlights work flawlessly, so I installed one of my fuses and tested the dash/gauge lights, and viola, all is well. I reinstalled the switch in the dash panel and checked it again, blown instrument light fuse again. I took the switch apart several more times and put it back together, as soon as I pull the **** out it blows the fuse. I've attached some pictures herein, please review them and tell me if you see anything amiss. Thanks for helping.

 

I am not an electrical engineer but it’s obvious to me that something is wrong when the switch has been reassembled. You may have a hard time finding a illustrated parts breakdown of the switch. I have read where the restoration headlight switches are troublesome, it may be wise to purchase a switch from Willcox as they test each switch to ensure it’s working correctly. You can also get a schematic of the wires going to the switch that may help you figure out what piece or pieces are causing the short.

 

When you have NO dash lamps, it is usually due to missing one (or more) grounding wire/strip to that dash area. The gauge cluster ground comes via a black wire from the trans tunnel area. The driver's dash ground comes via a black wire bolted to the driver's front door jamb; there is also a metal jumper strip that attaches to the tach housing and the speedo housing to pass ground.
NOTHING electrical works without BOTH power AND ground paths.

 

So you tested this out of the dash, but with the headlight harness connected? I just wanted to verify that all wiring was connected or not at this point? Was the fuse you used for testing still a 5 amp fuse?

It's very possible that something else in the harness is causing a short when you have the switch in the dash - maybe a wire that is positioned differently when the switch is in the dash as opposed to when it is out of the dash?

You might already know this, but the dash lights are wired such that the fuse doesn't get any power until the headlight switch is turned on. The switch itself provides power back to the fuse-block (dark green wire I think), through the 5 amp fuse, and then back to the dash lights. I can't think of anything inside of the switch that would cause the 5 amp fuse to blow.

 

I would probe each wire coming of the headlight switch connector, with the positive end of my meter, with the negative end attached to ground. The one that indicates continuity, that's the circuit I would investigate.