I've mentioned many times over the years here but once again - at least 50% of electrical problems are caused by a faulty ground. Gotta have a clean, bare metal to bare metal connection from engine to ground strap to firewall, and all other grounds must then be clean, bare metal to bare metal connections.

On our old trucks it's common for corrosion to have built up over the years. On mine I run short auxiliary ground wires from fender inner panels where electrical components may be located and therefore grounded back to the firewall. Add another couple of short ground jumpers from radiator support to inner fender panels. Add another short ground jumper or two from cab to bed. These ground jumpers have to be heavy enough wire to carry the loads of circuits, so at least 12 ga, if not 10 ga.

With these added grounds, clean bare metal to bare metal connections, the electrical circuits are furnished with a ground that's bonded to the engine where the alternator is grounded. On some components like regulators etc. I run a ground jumper wire from device case to mounting surface on fender or firewall. I also add ground jumper wires, bare metal to bare metal, from light sockets for headlights, tail/brake/turn lights to their mounting surfaces.

On top of that, every now and then you have to go back, loosen the screws and clean those grounds, like every fall so it's all ready for the winter onslaught. It can be good to give an extra ground at the dashboard too, depending on which model.

Once this is done it can only be the wiring, connectors or device that fails so a large part of 'potential' electrical problems is solved way in advance.