Cadillac Repair: 1989 Cadillac Deville wont start, no start, starter

Question
Hi Bill, a couple of months ago my sister bought my mother a 1989 Cadillac Deville (that is in excellent shape) when her 34 year old Volvo finally died. When she turns the ignition key the engine won't start. The electrical's working but engine doesn't start. We had this problem before so we charged the battery and the car started. Then we let it sit for two days, now the car won't start. Does she need a new battery or is there something she's doing wrong? Cadillacs are very complicated (compared to the incredibly simple Volvo). We're kind of overwhelmed by this car (not to mention the owner's manual) and all of its fancy electrical components/capabilities but I know its a great car and I'm sure after we figure out how to opperate it we will grow to love this car as much as our beloved (may it rest in peace) Volvo. Any advice you can give us would be greatly appreciated. Thank you so much,  Judy and Billie in San Diego

Answer
Hi Judy and Billie,  

          You are right about the Cadillac in that it can be intimmidateing with all the features that it has. And with the current modle cars it has only gotten more so. But the more you use the features the easier they will become and might wonder how you did without them.

          Lets start with the battery since it helped before. In order for the engine to turn over the battery needs to be at least 10 volts. However for the computor to function that is also the aprox. voltage that it will get confused and not know what to do. So if you battery is 4 or more years old I would replace it with the heavy duty battery that had around 770 CCA/cold cranking amps or more. If the battery is newer then something could be on and draing power after the key has been turned off. If you can remove the battery autoparts stores can test them for free and then you will know good or bad. Call ahead to make sure your parts store offers that service. If you have a voltmeter that reads DC volts make sure the scale can read at least 15VDC and touch the red lead to the battery positive and the black meter lead to the negative and see what it reads. A good battery will read 12.6V but 12 volts or more is good. Try starting the car in neutral. Maybe the neutral safty switch has burned contacts in park. Or with your foot on the brake hold the key in start and slowly move the shifter from P to OD and see if it starts. The n/s switch could be out of adjustment.

          If there is a Cadillac theft system there should be a light on the dash that will flash. If so then maybe the starter interrupt relay is bad and needs to be changed. It mounts below the steering column and has 4 wires...pink, yellow, yellow, black/yellow.

          The last possability is that the starter is bad. If you can slide under the front end with your meter put the red meter lead on the small terminal that the purple wire attaches and the black on clean metal like the engine block or the battery neg. bolt. Then have someone turn the key to start and see if you get a volt reading near battery voltage. If you do then replace the starter and solinoid together and your problems should be solved. Sometimes if I have a bad starter and it makes the differance of towing/pushing or driving I will take a hammer and tap on the big round part of the starter no harder than if you were to knock on a door. Give it about 7-10 taps and that might jar the starter so it will start and then you could drive it to your mechanic to have it replaced.

         Hope that helps. Bill