Hi Dave, Had similar problems, and Will told me how important a good ground is. With time, the path to ground from the dash to the Chassis, to the frame gets compromised. Try running a wire directly from the dash to battery negative and see if that solves the issue, and let us know if it did! Good Luck!
I rewired my truck with a modern blade fuse style harness and am having trouble with two of the lighting circuits. I keep blowing the fuses on the light switch and turn circuits.
I replaced the head light switch with a new stock style switch and the turn signal switch is an original Spartan SCS-3R.
The light switch handles the low draw light circuits (dash, interior and tail lights) but the head lights and high beams are on a separate circuit and are cycled by relays. The lights work for a time or two of cycling the switch, but eventually blow a 25a fuse.
The turn signal does something similar. I had it wired as a two pin flasher relay (working) and am trying out a three pin relay set up (not currently working but I don't know if my flasher can is any good).
I'm checking for shorts now but haven't found any yet.
My question is: has anyone else had trouble using the original style switches with a more modern setup? This occurred to me when I remembered the original harness used a single 35a breaker and I wondered if the switch itself is causing the problem because of it's construction.
My wiring diagram: https://drive.google.com/file/d/0BzyAcIpXncObS0lnVVVWbnBFaDg/view?usp=drivesdk
The signal circuit I originally copied: http://www.earlycj5.com/xf_cj5/index.php?threads/spartan-model-scs-3r-turn-signal.98976/
Thanks for any help you can give.