I have a problem with my 2000 Olds Bravada. When I start it up,the gauges and the dash test lights don't operate at first.The battery light stays on ,and the alternator is not charging.Sometimes everything goes back to normal in a few seconds. Sometimes not at all.The alternator tested ok.I looked in the owners book for a underhood relay that might be the cause,with no luck. Any ideas? It is a 4.3 L V6. Thanks.