was it wet or raining when the car plays up ? if it was check the main earth from battery to car and car to engine. i had a car once that i got cheap - because of the problems it was having - it always broke down when i was raining.... earth to the engine was corroded as hell.
My old man used to be an auto electrician - nearly all stupid faults are earth related.
a good test is stick your meter across the battery and start the car and watch the voltage as the starter kicks in. (it will drop but note what to and how quickly - its easier on some of the old swing meters)
then do the same thing from battery +ve to car body - should get identical reading
and then +ve to engine earth . (difficult i know as battery in front and engine in back)
if any are different to the battery only test then that earth is bad.
if your main earths are old then change them anyway.
hope this helps....

