I have a 6 cylinder 68. Went for a drive today, came back and parked in garage, turned ignition off. All OK. A few minutes later I decided to move the car, turned ignition on, car tried to start very slowly and sporadically (I just replaced the solenoid a few weeks ago), but this was now acting the same as when the solenoid went bad. So I turned ignition off but car kept trying to start, so I hopped out, disconnected the positive battery cable, then noticed that the negative battery cable was smoking, so I disconnected that. Would a solenoid cause this? Bad battery? Any help is appreciated. Thanks.

 

Sounds like you have a dead short to ground somewhere.

 

Low voltage at the battery, or a loose or dirty connection on one of the large cables will create a large amount of amperage draw which can weld the points in the solinoid and make it continue to crank. I would clean all the cables, smack the solinoid a few times to try and free it so it wont crank on it's own, then if that doesn't cure it do a load test on the battery. If you do not have a load tester visit a mechanic, don't go to one of the discount auto parts stores, they generally will test it for free but have no idea how to test it, better to have a good mechanic test it for you, most will do it for nothing.

 

How do you turn the ignition off and start the car? Sounds to me like the regulator cut out points are not opening. Check that the problem is not with the regulator. When the engine stops, one set of contacts in the regulator opens so the battery does not try to drive the alternator. If these don't open then the battery will try to turn the alternator and draws a lot of power because the alternator turns into a motor and tries to turn the engine. Could also be that the diodes in the alternator are bad, and the smoking came while you were driving. This would mean no charge in the battery A stuck solenoid would always be trying to crank the engine so there would be no difference if you tried to start the car or if you didn't. The starter would always be engaged. Could cause smoke but you would know because you would here the engine cranking.

 

This sentence is absolutely wrong. Low battery voltage, loose or dirty connections will HINDER current flow, reduciung amperage, not increase it.

Where did you learn this?

 

Do the math, Why do 6 volt systems use battery cables twice the size of 12v systems???

You would be correct if there was no power draw. That is why they tell you it is cheaper to run your electric cloths dryer at night when most people are not using power, because the source voltage is higher, and you pay for wattage use, and the wattage is lower.

Power(watts)=voltsXamps

If your starter requires 600 watts to turn the engine, and you have 12 volts, it will take 50 amps of power. If you decrease the voltage to 10 volts, it will take 60 amps to turn the same engine.