One thing I have found is that the Harness which carries the starter cable can become very degraded and cause strange symptoms - like all the warning lights coming on and off. There is also a wire that goes to the Oil sensor on the exhaust side that is routed under the timing belt cover - hard to see on t dirty engine that sometime gets grounded to the body after much wear. If you have the older style harness prone to internal melting - that may be a place to look - mine was fine on the outside but the after splitting found all sorts of wires badly corroded.