Pontiac Repair: charging, pontiac bonneville, volt meter

Question
hi my mom has a 2001 pontiac bonneville when she starts it the guages (volt) goes up to 18 for a few sec. drops to around 12 and about 10 sec later down to zero I checked the terminals on battery they are tight and did little more than wiggle the wires on alt. to make sure they were tight any idea

Answer
Hi Rocky:

first off check to see what the battery voltage actaully is with a volt meter. That car has a module called a dash intigration module that runs the insterment cluster You could have an issue with the dash module not reading correcy battery coltage and in turn is giving the gauge the wrong reading. Or it can just be the gauge is bad. With out the use of a scan tool ther is really no way to tell for sure unless you have a wiring diagram for the dash module and make sure you have full battery volatge on all the power inputs to that module and that the gound(S) are good to that module as well. My guess is that it's a bad cluster assebly but the fact that that is driven by another module makes me a bit leary to say for sure that is the problem..
Good luck :)