I wanted to share my experience I have had with lighting system issues and what I have done to fix it all.
*I have set out to completely replace and update all of the wiring so I have made drastic, custom changes and am completing it in stages that I do on a rainy Sunday every so often.
The truck I am doing this on is a 76 camper special that has been rebuilt using a 78 cab along with a *******ized harness that has sort of combined the two. The main differences were the steering column and the horn system, but staying with my 76 column made it right. One thing that is unique to the camper special model, I assume, is that there is a 5 pin connector for lighting behind the cab on the frame rail. In my experience, diagrams for standard trucks have worked fine including color-coding of wires.
I had an incident that ended up with brand new front grille and RF fender and apron, so I relocated my battery to the bed and I relocated the starter solenoid/relay to the LF apron. I deleted the wiring for duraspark ignition by going to an MSD ignition box, and upgraded to a 3g alternator eliminating any need for any wiring at all across the RF side, except for the lights which I replaced this weekend. I have replaced all of the original harness connectors with terminal strips as well because they were in such bad shape. This makes it easy to go thru with a test light!
I built a new LF light harness from scratch and connected to my terminal strip for lighting.
I did the same for the RF lights except I changed the design to run across in front of the radiator support and meet up with the same terminals where the LF are. Doing this cleaned up the right side harness drastically. I had to retain the white/blue wire for the RF blinker function which stemmed from the harness coming out behind the RF cylinder head area and route it across the firewall through looming (which I have the alternator power wire and blower motor wiring in as well) and over to my light connections on the LF fender. What I use is the 4 wire trailer wiring so everything makes since and I break out with the standard 4-pin trailer connectors, too so that it can be disconnected easily. I replaced the harness to the taillighting by running trailer wire as well. I retained the original portion that feeds the camper plug and fuel tank wiring so that everything works but the rear lights are effectively bypassed.
so now everything works like a charm, where before I only had hazards working in the front and I did not have any blinkers at all. I discovered a fuse issue for the turn signal circuit, I had to clean the fuse box terminals with sandpaper to get proper voltage restored. I had a confusion getting the brske lighting figured out since it uses the hazard fuse circuit. (None of this worked, so I had originally made a new circuit for the stop light switch and brake lights which bypassed this, but it all works now)
One of the issues I had with the blinkers in the past was that none of them worked and the right side cluster indicator was always illuminated. So I assumed that my turn signal switch was bad and planned to bypass it all by another means, but I pulled the steering wheel and everything seemed okay with a test light off of the six points of the hazard switch. I believe that all of my issues were caused by the crusty 4-pin connectors for the original light harness connectors, bad ground wires(I added individual ground leads for all six front bulbs instead of splicing out like the originals are done) and the fact that the old wire insulation was so bad that it cracked every time I tried moving or bending any wires.
my next additions will be adding in headlight relays similar to the lmc truck headlight harness( I had that kit before and had issues with it not being long enough and the relays were cheapos) and I am goin to add an accessory relay to replace everything that is fed by the ignition switch for key-on(run) power and feed it with my add-on modern fuse panel. This way I add new things easily and not pull too much from the ignition switch. I am going to have a common point that will act like a separate fuse box for key-on power so my tach, electric fans, radios etc will all come from there.
I know this was long winded by I really wanted to share what I have done because I fixed so many functions that are a constant headache for everyone in a manner that is much more long-term compared to splicing in New sockets here and there and keep having connection problems with the old wiring.
. Long story short, I highly recommend building new light harness sections from scratch and I would be happy to make some kind of instructional on how to do it with a parts list too if anyone is interested. I don't keep up with the forum like I should, so feel free to send me an email at clprsx8976@gmail and I will be able to answer much quicker and be able to send someone pictures that way as well.

 

Good job. Lot of work, but the fact that everything works now means it was worth it!
Well, it was worth it for us anyway, since you did all the work...

Did you use the terminal strips with stainless steel screws and buss-bars? I've used some that I thought were stainless but that rusted up pretty quickly. A good stainless one should outlast the truck.
I know they don't look very high-tech to most, but they are one of those "functionally beautiful" bits that are WAY better than broken, corroded and loose old wires and connectors.

Shoot some pics sometime and post them up.

Paul