Maybe start by checking the grounding from negative battery terminal to chassis with a DMM (digital multimeter). Disconnect negative battery terminal when running another piece of 8 gauge from neg battery terminal to chassis ground point - this can be a quick cure for the cause of many mysteries like what you have described. Error codes next (or before), best done with an ALDL to USB cable into a laptop running EFILive. If no cable etc, then just bridge A-B on the diagnostic link (under passenger side glove compartment) with a paper clip to read the codes via the instrument cluster's intermittent flashing of the check engine light. Process of elimination is the key here, I'm certain it will be an earth issue of some sort, but in saying that corrosion on the globe terminals could also be a factor or incorrect wattage globes in headlights, or blown globes in cluster etc..