1970 F100 85% restored. All was fine and then instrument panel lights not working.... think the fuse may have blown but bypassed it and lights worked for a while but then dash lights went out again after short while...... Did I blew up the rheostat on the light switch? How can one test the rheostat? The dome light still works.... honestly its been too cold to investigate this much but was hoping the circuit is simple enough to gain some insights from the experts here
Eric
Richmond, Virgina
1970 F100 project?
1971 F100 donor
When you bypassed the fuse, how long did the lights work?
I ask because there was a reason the fuse blew. If there was a wiring fault, you really need to track it down. The safest way to do that is to substitute a small, 12 volt bulb for the fuse. That way, the bulb will normally illuminate at some level until you clear the fault. I had a similar problem once and I soldered two wires to the blown fuse and put it back in place. That provided a means to connect an ohm meter or a bulb.
I don't suppose you made any changes to the dash lights like the bulbs or the cig lighter, radio, etc recently. If so, any of those could be a factor.
You could have a bad switch or even a bad connection.
Did you check the fuse to verify its condition?
Bill
68 F100 Ranger
73 F100 Ranger XLT
Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in garages. (Apologies to Kenneth Grahame.)
Weill not really sure how long it lasted..... at least a hour or so I would guess total.... its not my daily driver and out at night even less....unfortunately when I removed the fuse the first time it broke so could not verify it had indeed blown or what happened. I had not done anything recently unless a ground up restoration counts. I did not do anything with wiring though..... I am guessing a short near ashtray light or something.... really need to get out there with meter or test light.... I was curious if you knew how to test the light switch itself (rheostat) as that's the most expensive component that I might need to replace....
Eric
Richmond, Virgina
1970 F100 project?
1971 F100 donor
well, FYI everyone....finally had warm day combined with some time to tinker with my truck. Replaced the headlight switch and problem resolved. Was happy to learn that O'Reilly's carried the switch in stock But was frustrating install given they give very little thread to catch with the spacer and all. But its all in and operating correctly!
Eric
Richmond, Virgina
1970 F100 project?
1971 F100 donor
Believe me, my young friend, there is nothing - absolutely nothing - half so much worth doing as simply messing about in garages. (Apologies to Kenneth Grahame.)
think the fuse may have blown but bypassed it and lights worked for a while but then dash lights went out again after short while...... 
Did I blew up the rheostat on the light switch? How can one test the rheostat? The dome light still works.... honestly its been too cold to investigate this much but was hoping the circuit is simple enough to gain some insights from the experts here 
I had not done anything recently unless a ground up restoration counts. 
I did not do anything with wiring though..... I am guessing a short near ashtray light or something.... really need to get out there with meter or test light.... I was curious if you knew how to test the light switch itself (rheostat) as that's the most expensive component that I might need to replace.... 
But was frustrating install given they give very little thread to catch with the spacer and all. But its all in and operating correctly!