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I have a 1998 Pontiac Bonneville SE 6cyl 3.8L that is giving us quite a challenge. Sometimes it won't start, and sometimes when it is running (driving or idling) it will just turn off. Sometimes it will re-start right away, and sometimes it won't. The period of time during which it won't start can vary from a few seconds to several days. We initially thought it was the fuel pump, since normally you can hear the fuel pump pressure up when the key is turned on, but when it won't start, you don't hear the pump at all. However, we also discovered that when the problem is occurring, the power windows will not operate. All the other electrical components seem to work just fine. The mechanic has replaced the fuel filter
"just in case" (before we discovered the window issue). He finally decided it was the ignition switch module, and replaced that. The car ran fine on the way home from the shop, and the few times we've driven it since. This week, the problem started up again. My guess is that there is a common electrical element with the fuel pump or other ignition component, and the windows, but I am clueless as to what it is. Any ideas? When it does start and keeps running, it runs great, no different than it always has. It will turn off regardless of whether the car is idling or running down the road at 70mph, although it seems to be more frequently when the car is idling or going relatively slow.

Thanks for any insight anyone can give me!  

wow... what a nest of problems....

it really does sound like  the ignition switch....  i wonder.. if you can ask the mechanic who put it in... was the box he got it out of ... sealed??????  is there a chance that somebody had swapped parts and returned it.. only to have it installed on your car...

it has happened...  i have opened boxes of parts and found used parts that got returned..

got a test light....  or know how to make some....    there are a few fuses you need to monitor...

fuse 1D, 5 ,6 , 7, 7E,  8, 10   all should come on  with the key.... and stay on. with the key..

fuse 4 should have power all the time...

the above fuses control the engine controls...    

i was over at autozone .com looking at wiring diagrams..  but i really cannot find the exact diagrams that shows power distribution..   new cars have dozens of pages of diagrams..

the engine shutting off could be also several problems...  

wiring problems...

bad crank sensor..  bad oil pressure switch.. if it is a 3 terminal switch is also controls the fuel pump.. as the fuel pump relay only stays powered for a few seconds..       so you also need to monitor the fuel pump power wires to the back of the car..

is the fuel pump noisy???? is it possible that you got a bad blend of fuel.. too much ethanol...   that would not stop the windows from working..

bad ground are also a problem..   clean the battery cables at the battery...  clean them at the block...  clean them where the ecm harness hooks to the motor...

before doing any thing ... have it scanned for codes..

post any that you find..  

Had the same problem with my bonneville (98) after several trips to repair shop, "I" discovered  the multiple cable connections on the positive battery post could not be tightened securely, as the bolt would bottom before the connection was "really" tight. a  shorter bolt cured the problem. Due to the fact that there are multiple cables at times part of the electrical system would work.