79 Cadillac Electrical Issues

1979 Cadillac Fleetwood, 74,000 Miles, 425 engine.

My headlights keep dimming down, there may be a short somewhere? I replaced the alternator, battery, battery terminal ends…The power still is draining somewhere. I have no idea where to go from here…Thanks!

79 Cadillac is a major bucket of bolts. It must be the worst one ever. I would first check the engine to body ground wire/strap. A 72 model had one down by the right exhaust pipe. My 72 burned off from contact with the pipe. I had other GM (we’re not trying) cars from the 70’s that had ground problems. Once fixed, the electric windows, lights, turn signals and wipers start to work properly.

The dimming lights means there is a voltage drop problem somewhere. This is most likely due to a bad connection somewhere. It could be in a power connection to the lights or a ground connection. Try cleaning the chassis grounds under the hood. If that doesn’t help check the voltage getting to the lights using a known good ground point for a reference and see if the voltage is low compared to the battery voltage. If it is then follow the line back to where it is a good level. The problem on the lead will between those areas. I would say that anymore than a 1 volt difference between the battery voltage and the voltage at the lights is a problem. There will be some voltage drop that is due to normal wire loss.

After 31 years, ALL the connections are bad. Make sure both the engine block and the car body are connected to the negative battery terminal (ground) with good, clean connections. Then check the positive cable terminal on the starter. It must be clean and tight as the entire car is being supplied with power from this point…

Thanks for the input, I will give the suggestions a try. Also, When the ignition is turned I have to pump the gas pedal several times before the engine turns over completely. is this a problem with a dirty carb? Maybe a bad starter? This car was my grand dads and I don’t know anything about older cars…Thanks for the advise!

Do you have to pump the gas to get the engine to crank, to turn over? Or does it crank OK but it just doesn’t start…

Pumping the gas to get it to start usually means the choke is not working…

Back to the voltage. Measure the voltage across the battery with the engine off. A good fully charged battery should read 12.6-12.8 volts…Start the engine. The voltage should jump to 13.2 or so and then slowly climb to 13.8 or 14 volts. The outer headlights have three wires. The inner high-beam bulbs will have two wires. One of those wires is a ground, the other is “hot” when the lights are on. Measure the voltage on that connector. It should be within one volt of what is available at the battery.

Are the headlights the only thing dimming down or does this apply to taillamps, dash lighting, and other accessories also? (wipers slowing down at idle, etc.)

The whole deal : headlights, Power windows, radio, dash lighting, it will all dim down…I can idle the car just fine-It can sit and run and the power all works. Just once I get going any distance the whole thing dies…

Yes, I have to pump the gas several ( 3-5 times ) before the engine will fire up.

I will get a read on that voltage in the morning. Thanks for the help!

The car was my grand dads… He passed and I inherited it. Glad I got into such a reliable vehicle…I will check out the grounds, Thanks!

If all the accessories are having trouble then there may be a problem with the main power lead that ties from the battery to the main power panel which may be under the hood area. The trouble could also be due to a bad ground from the battery to the chassis. Make sure the charging system and battery voltage are ok when this trouble happens. The alternator may have a problem. To help find the trouble area you could run test leads between the battery and the suspected trouble area. You can do make a ground or power lead jumper, or both. It will give you a quick way to find out what is wrong.