Where is ground located on chassis? 91 grand marquis?
Negative Battery cable runs from battery to frame and then to engine cable corrodes at frame which gives you a bad ground. to fix it is best to get two new negative cable to replace the old one. one cable from battery to frame the other from frame to engine. make sure you clean any coeeosion on frame to ensure good connection.
While you have things apart, change all 4 leads. You have 2 negative, one to the body, on the inside of the front fender, the other to the engine block. If that cable is deteriorated, you can bet the positive is, too. That one runs from the positive battery terminal to the starter solenoid. The 4th lead goes from the solenoid to the starter motor. For the positive, engine ground and starter cables, I always use 1 gauge. The up charge is about $10 total for all 3. 4 gauge works very well for the body ground. When you do the positive, make SURE the negative is disconnected from the battery, or you can give yourself a heart stopping shock. Remember, too, after you reconnect the battery, you have to teach the car how to run again. The procedure is in the owner's manual, but if you don't know it, it is as follows: 1) Start the engine, a/c off, and let it idle 5 minutes in park. 2) Put car in drive a/c off and let it idle 5 minutes. 3) Put car back in park, a/c ON, and let idle 5 minute. 4) Put car in drive, a/c ON, and let idle 5 minutes. Do not touch the throttle during this procedure. If the car stalls, and it almost certainly will when the a.c is on, just restart the engine.
Thanks for all the help I got it running