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Ok, so after reading several posts on wiring a truck, I jumped into my first attempt at wiring and trouble-shooting today. I am definitely an electrical noobie, so any advise would be welcome.

My '49 was re-wired by the PO who used a "Factory Fit" harness kit, and from what I can tell by looking at the fuse box, regulator, ignition, light switch and gauges, they all appear to match the wiring harness diagram. The back half of the harness was not installed, so that served as my primer in car wiring.. Simple, right? I plugged in the connector under the cab, temporarily connected the tail light wires and was able to get them to light up when I pulled the cab light switch in both position 1 and 2. Minor success, but that is all that happened with the tail lights. Turned off the light switch, and with the ignition on, the brake light would not trigger the brake pedal, so I started poking around the brake switch. I cleaned the posts and re-tensioned the connectors first, then when I did a continuity check on the switch by touching both posts with the multi-meter it read 1.0 (no continuity - makes sense with no pedal pressure), and when I pulled the brake pedal rlever (under the hood) by hand, it registered .01 meaning had continuity, so the switch seems to be working. Stumped by that, I then moved under the dash to see what else was going on with everything else.

So several hours later, with a stiff neck after contorting myself under the dash, I have a bunch of questions:

1. Brake light? Why is it only acting as a driving light and will not trigger from the pedal switch
2. Headlights - low beams do not work, only high beams after stepping on the high beam switch (even with the high beam fuse PULLED!....) I guess both low beam bulbs could be out, but that would be too easy...
3. Fuse box - high beams show full continuity regardless of the fuse being IN OR OUT. All other fuse terminals seem to behave normally with no continuity when fuses are pulled. To make sure there was no weird connection between the high and low beams, I put a fuse in the high beams, removed the low beam fuse, and the low beams did not show continuity (expected) with the fuse out, so they seem to be separate. I could not see any exposed wire or anything that could bridge the high beam fuse terminals at the fuse box, so I am confused as to how it can magically work with the fuse out (Not sure when it happened, but I noticed that the high beam fuse was burnt through. The right side headlight fizzled down to a dim glow not long after firing the lights up for the first time)
4. Dome light - doesn't seem to work. Registered 6.38 volts at the lead wire, have a good 6v bulb, cleaned up the switch with contact cleaner and even tried a brand new out of the box dome light left by the PO and neither fixture would light up regardless of dome light switch position or dash light switch position (I believe this one is always supposed to be hot). I took two wires soldered to a 6v bulb, grounded it to the cab, then stuck the other side into the dome light lead wire, and it lit up, so I am totally stumped on the dome light fixtures not working. I even checked continuity of the short wire from the dome light switch to the bulb socket, and it showed continuity, so something is happening between the lead and the bulb in both dome lights.

I have read that a "bad ground" can cause issues with electrical systems. Is that what I am dealing with?? If so, how do I track that bugger down as a one man operation?

Sorry for the long post. Trying to get everything working properly, and prevent an electrical fire which would suck after years of messing with this project!
Thanks,
Sulli

Forgot to mention it is a 6V electrical system with a generator that seems to be charging and the new 6V battery has been on a battery tender since new.

You will find there are or should be several braided ground straps. Find and clean the mating surfaces very well. Must be bare metal to bare metal. Then run your tests again.🛠

- ground cable/strap from battery to frame
- ground cable/strap from frame to clutch-housing
- maybe a ground strap from block/head to firewall?
- maybe a ground strap from steering column-side from frame to clutch-housing?

Darn autocorrect! RR fixed it for you.

Martin and Tim, I found two ground straps (dash to engine and block to frame) and the ends of the frame/block strap was looking a little grungy, so I cleaned both ends, the attachment points on the frame and block and reattached them. Both straps had good continuity, so I moved under the dash again, and figured out that it is the low beams that are working, but not the high beams (I guessed yesterday, but confirmed with the multi meter that voltage flows to the low beam wire only. Hi/low beam switch is good in both positions confirmed by switching the low beam wire to the hi beam post and getting it to light from either post)
When I pulled the headlight switch from the dash, it looked grungy and didn't operate smoothly, so I blasted it with contact cleaner inside and out. Started checking continuity across all terminals by leaving one probe in the power feed terminal and touching all others until I got them all to show continuity with the switch in position 1 and 2. There was something that looked like the points in a distributor, so I ran some fine sandpaper through them to get some fresh metal showing. Threw the switch back in the dash and some success! I got dash lights to work but no dome light even though the dome is getting juice.
Any thoughts on why the high beams don't work? I'm still confused by the continuity of the hi beams at the fuse box with the fuse pulled. I checked voltage at the high and low beam fuse terminals, but didn't get 6v, it was .15 for high beams (fuse still pulled) and .05 at the low beams, so I have no ideas on this one.
Brake lights still only light up as a running light and only one wire is hot when the switch on. Neither the stop nor tail lamp wires were carrying any voltage at the fuse box with the light switch turned on which is weird if I can get the tail light to turn on.
I feel good about today's limited success and even got the radio to light up (but no noise), but can't get the headlights or tail lights sorted yet.

Remove and clean up the floor mounted dimmer switch.🛠 If you’ve already done this disregard.

Ok, I haven't done that yet, and will give it a shot to see what happens. The switch seems to be working from what I can tell when I do continuity and voltage tests and pushing the button (one reads off and the other reads on and vice versa when I toggle the button).

What should the multimeter be picking up at the fuse block in volts? I'm getting very little to none when I test. A probe light isn't even lighting up.

Correction, probe light comes on for low beams, tail and stop lights

Weird... I still haven't "cleaned" the dimmer switch, but I guess several cycles of the button effectively cleaned the contacts enough that I now have high and low beams... At least it's not a wiring issue.

Down to tail/stop lights and the dome light, and I should be in business!

Problem will return if you don’t clean the switch contacts. They live in a dirty environment and need a wire brush now and then.🛠