Chasing a gremlin

[BIGJAYHOO]

Hey guys, I’m having a mysterious issue with my 81 c10, after the truck has been running for a short time, it will shut off (engine & all electrical, like the battery has been disconnected) the has happened when hitting the floor dimmer switch, wiper/washer, fan speed, shifting from drive to reverse/park. It is getting more consistent & frequent. I’ve checked around for loose connections & signs of a short, but coming up with nothing. Does anyone know of any common area I should be looking at that would be affected by all the switches?
The truck does have an “LS” swap, all LED lighting inside & out, & LED JW speaker headlights. All of which have been on the truck for about 3-4 years now. Nothing has changed recently. I put around 1000km on the truck every week

[Rickysnickers]

First start by checking all your grounding points. How many ground cables/wires do you have? There should be at least four grounding points.

[BIGJAYHOO]

What would be a common ground for all those though? & any idea where it might be?

I’ve checked the grounds I can see under the dash & near the battery

[Rickysnickers]

Sorry, but I'm not terribly familiar with your truck. There should be grounds on the engine and or cylinder head(s) to the frame, the battery to the frame, the cab to the frame and possibly the bed to the frame, as well as those under he dash as you mentioned.

[Dead Parrot]

Check the battery cables for internal corrosion. The outside rubber can look great while the copper inside is rotten from years of acid exposure.

Check the junction block. If original, it is about 42 years old. Make sure everything is clean and not burnt.

2nd the check the grounds.

I don't know where the LS grounds the neg battery cable but the older SBC often used the alt bracket. If the bolts on that are loose and/or corroded, could explain loss of both battery and alt power at the same time.