My 99 deville d'elegance overnight starts up fine with 14.2V but as it warms up, the volts start dropping to 12.5V...when i turn off radio and AC it jumps up to about 13V. I replaced battery, alternator(correct amperage), belt, spark plugs, cleaned throttle body. I know how to maintain my car but this is frustrating. My knock sensor makes noises sometimes but quits after awhile. My coil packs make a ticking noise, not a marble in a jar noise(made marble noise once). What is my next move, start moving grounds to different places?

SOURCE: Have 1994 Cadillac Eldorado won't start without jump

Check the NEGATIVE battery cable from the battery to the ground pont

SOURCE: Car won't start, battery power loss could it be the alternator?

Alternator should have better than 13.5v output with all accessories on including headlamps.Check with volt meter right at battery terminals (running) If not it's not working properly. Doubtful from what you have said that starter is bad. Also check that terminal connections are clean and tight on battery.

SOURCE: have a 99 cadillac sedan deville. lots of

you need to verify the dome lights are turning off before you walk away,something is draining the battery.check you car out after driving it and make sure radio and any other things all shut off.

SOURCE: 1991 deville idling very ruff

Hi you should change the coolant temp sensor this is a white sensor on top of the intake and is part ot the computer system.

SOURCE: I have a 98 cadillac

The clicking noise is usually the starter solenoid failing to engage. In your case it sounds like it is just barely starting to fail and the new battery simply gave it enough juice to overcome and start. I would expect the problem to return soon. When it does, locate the starter and give it a few light taps with a hammer or other weighted object while turning the key. this should enable it to start. In that case you will need to replace the starter.