94 lesabre 3.8 intermittent no headlights/ gauges

When started ses light comes on headlights won't come on, temp gauge climbs above 140, batt shows discharge, battery actually is charging, fuel gauge ok, but yellow light on, oil gauge ok speedometer shows 60-80 km standing still, tack between 0 & 1000. Car runs fine. Sometimes suddenly everything is ok. Once it's ok it stays ok untill turned off. Then same thing again. Took it to dealer. $200 later they said they can't find problem, want more time & $. They said it's wiring problem. I disagree. If it was an intermittent it should also cut out. But once ok no amount of tapping, wire wiggling will cause it to fail. PCM is ok. I'm thinking either BCM or a weak relay - once it pulls in it's ok. Any suggestions? I'm trying to get a decent wiring diagram, but so far no luck. Sorry for being so long winded, & thanks in adcvance for any suggestions