[Gerry Zagorski]

If it works fine when the engine is running then I think you might have a weak battery....Do you have an engine starting and a separte house battery for your electronics?? If so, I would have your house battery load tested.... Most any auto parts store will do this for you free of charge.

If you only have one battery and the engine starts fine, like Frank said it's proabably something in your wiring that you will need to trace with a volt meter.