Strange electrical issues with my '72 Dodge truck

[MopaR&D]

I've had this truck a few years now and when I first got it I removed quite a bit of add-on wiring that previous owners had put in, I assume for powering stuff in their camper as that's what this truck spent most of its life as. One issue I still have though is if I go to crank the engine with the headlights on it instantly blows the fuse for the instrument panel lights. Every time I drive at night I have to make sure to start the engine BEFORE turning on the headlights or my gauge lights go out and I have to fish around for yet another fuse. I've also noticed at night when the engine is running the turn signal lights in the gauge cluster flicker very dimly (can only be seen in darkness/at night). What the heck could cause this? Btw I converted all the bulbs in my instrument cluster to LEDs and they themselves all work fine.

Not sure if it's related but I am planning to replace the alternator soon as the bearings are pretty noisy and as far as I can tell it's original or just very very old. Some of the wires coming off the alternator are also not in great shape and I plan to cut back the wires and re-splice new connectors on the ends. Any and all advice is appreciated.

OH and one more thing, apparently it's a common issue for the main power feed wire going through the ignition switch connectors (located under the steering column) to overheat and melt/blow out, one of the first repairs I had to do on this truck was a new ignition switch and new connectors for the bigger wires. Supposedly the main cause is too much current draw from the heater blower motor so I always keep it on Low or Medium fan speed, haven't gotten around to putting it on a separate circuit as the fan blows plenty of air on the lower speeds.

I did go through and redo all the grounds I could find between the engine, frame and cab.

 

[jos51700]

I'll wager that the headlights and/or dash lights have been run off the same circuit as the starter so it's overloaded them when they're on. Think parallel circuits.

I'd run the headlights off a separate relay and see if that fixes that problem and if not, it's still a worthy upgrade in it's own right. @crackedback has kits but not sure if they do trucks.

 

[MopaR&D]

I'll wager that the headlights and/or dash lights have been run off the same circuit as the starter so it's overloaded them when they're on. Think parallel circuits.

I'd run the headlights off a separate relay and see if that fixes that problem and if not, it's still a worthy upgrade in it's own right. @crackedback has kits but not sure if they do trucks.

Makes sense, I'm not sure if that's how it's wired though. As far as I could see that part of the wiring is still factory. I need to get a FSM for this truck, I got a Chilton's manual and of course it's basically useless, the wiring diagrams in there didn't tell me a whole lot.

 

[jos51700]

Makes sense, I'm not sure if that's how it's wired though. As far as I could see that part of the wiring is still factory. I need to get a FSM for this truck, I got a Chilton's manual and of course it's basically useless, the wiring diagrams in there didn't tell me a whole lot.

Yeah those Chilton's are barely worth using to start a bonfire. I can't recall seeing any digital versions of the FSM's for those trucks but if you do find a source, please share!

 

[MopaR&D]

Well I found a bunch of sites trying to sell paperback copies for way too much and pointless CDs with a PDF on it (it's not 2004 anymore guys come on lol) but finally came across this site that actually lets you directly download a digital copy. Wow! lol

Service Manual, Repair Manual, OEM Factory Service Manuals for Autos & Trucks

Looks kinda sketchy like the site was made in the early 2000s and never updated but the reviews seem legit, I think tonight when I get home I'll buy one and see how it goes. Or put on my pirate hat and see what I can find that way heh heh, damn things should be free anyway.

 

[RedFish]

I've had this truck a few years now and when I first got it I removed quite a bit of add-on wiring that previous owners had put in, I assume for powering stuff in their camper as that's what this truck spent most of its life as. One issue I still have though is if I go to crank the engine with the headlights on it instantly blows the fuse for the instrument panel lights.
OK , if this is automatic on the column, the orange wire in that harness connector comes down the column from that lamp, not ignition related. They just thought, there are extra ports in this connector, we'll poke the orange wire in it. The aftermarket ignition switches meant for one size fits all has a small black wire that will connect to the orange wire if you just plug it in as is. So to fix it, take the orange wire away from the switch connector. Use male and female spaded connectors to connect orange to orange. As many times as I have done this, I never checked to know if that extra little black wire is hot or ground. Bottom line... you dont need it. Leave it in the harness connector connecting to nothing on other side.

 

[cudamark]

As RedFish mentioned, it might be related to your ignition switch swap and a cross-wiring issue. What brand ignition switch did you use? Another possible cause might be improper, missing, or corroded ground(s). In the start position, that has the biggest current draw of any stock system. If you don't have sufficient grounding, the current will try to find another way to ground, sometimes that being another circuit or even hard lines and/or braided cables.