71 Demon Voltage Issues

My brother has a 71 Demon with a 360 and electronic ignition. He's unable to enjoy it because any time he starts it voltage spikes and blows the 30amp fuse he has in place if a fusible link. He's replace the voltage regulator and alternator numerous times to no avail. The high voltage is coming from the alternator. He can pull the wire from the alternator that connects to the big post on the starter relay and he can run the car off the battery all day long. Something else he's noticed is the ballast resistor gets boiling hot, even with the car turned of and key just in the on position. I'm going down there tomorrow with a multimeter and power probe to have a look, but wanted to ask here if anyone has any idea what's happening here. The entire wiring harness in the car is brand new from headlights to taillights. Something is obviously shorted or connected wrong...I'm just not sure what, yet.

Verify keyed 12 volts at the voltage regulator blue wire. If the regulator does not see 12 volts or battery voltage it will overcharge.

I had the same problem with one of my Coronets. I added a ground strap from the voltage regulator to the engine block and the problem was solved.

Charging system problems that exist after replacing everything more times than not boil down to not having good grounds. And it's not confined to just the charging system, lighting and accessories are also subject to grounding issues. It's easy to overlook the fact that the chassis is the negative side of the entire electrical system.

a 30amp fuse wont work inplace of a fusable link

Wow....
The “spike” that’s killing the fuse isn’t voltage...it’s current.
It’s not coming from the alternator, it’s coming from the demand (starter and ignition).
Ballast resistors run hot...that’s normal.
As Dakota stated, you can’t use a 30 amp fuse in place of a fusible link...two different animals.

Replace the fuse with a proper link.

In this case the high current probably is coming from the alternator and going to the battery.
I say that because (a) he started the car with the alt disconnected and didn't blow the fuse.
(b) starting current to the starter relay and ignition should be around 5 amps.

When the battery is low after starting and at fast idle its not surprising the alternator if its half decent will briefly supply more than 30 amps to the battery.

To find out if there is a high voltage problem, connect a voltmeter to the alternator output stud or the battery positive.
During start, voltage will drop - as low 9 volts. If its down around 9 V - the battery probably needs a good charging or replacing.
Running, it should be over 13 and below 15 V, depending on temperature, the regulator and how much resistance there is the in lines to the regulator.

Bottom line, there should be a fusible link. If it was replaced because it showed damage or melted, then find the source of the problem.

Very briefly after starting, current flow should look like shown with the orange arrows.


When the battery is recharged, it should look like this.


Ballast resistor gets exrta hot with switch when the distributor is not turning because the coil is getting continuous current. It's like having the points closed.
DON'T DO THAT for any length of time. It's not good for the coil or the ecu either.

Fuses blow fast under load where a fusible link is built to take the spike and only blow if there is a heavy or long draw. Fuse won't replace fusible link.

I fixed it, at least for the short term. I'll tell him to replace the fuse with a correct fusible link. The problem was actually a Mallory coil he had in the car from the first day he started it last year. Since last year he burned up two Mallory Hyfire 6A boxes, blew all his lights out once, and lastly couldn't start it with out a massive amount of current blowing the 30 amp fuse he replaced the fusible link with. Bottom line, the coil was drawing way too much current causing a massive voltage drop from the voltage regulator, in turn making the alternator think the battery was super weak, in turn causing the alternator to "charge" at 18+ volts. I had him replace the Mallory coil with a factory style coil and the problem has been solved. He claims the car hasn't run this good since he first got it running over a year ago. That Mallory coil has been bad since day 1.

Interesting, I wouldn't have seen that coming. Congrats on identifying and solving the problem.

Yeah, me neither. I was checking voltages and noticed on the coil side of the ballast my voltage was like 9v, but 11+ on the other side. I pulled the wire going to the coil and voltage came up to 11+, so I knew at that point something wasn't right with that coil. I read somewhere some aftermarket coils are wound differently to create more voltage, but at the cost of causing more of a amp draw. So, I threw a stock coil on and it runs great now...

That's exactly how your new coil will act as well.

You have two issues. 11v at the feed side of the ballast is way low.

Your aftermarket coil may have been designed to run WITHOUT a ballast so you were more than underfeeding it if you ran a ballast as well.

Exactly what Sniper wrote.
When current flows through a resistance, the voltage drops.
That resistance can be the filament in a light bulb, the inductive windings in a coil, or a resistor.
When there is no flow through that circuit branch, then there is no voltage drop.

On a normal inductive ignition, the points (or equivalent) open and connect the circuit so while the engine is running at low rpm the meter may show the pulsing of voltage as the current stops and then flows.
That's not to say the mallory coil was good, it very well may have been bad. It's simply to explain that the volt meter readings like that, with a key in run, engine off, could be considered normal.
It might be worth checking now with the engine running so you'll have a baseline for any future checks.
The mallory Hyfire 6A is a capacitive discharge ignition. Those send a powerful electrical pulse through the coil primary system. When something like that is wired in the ballast resistor is out of the picture as far as power to the coil goes. In many cases it does no harm to leave it.

Think of current as electrons moving like water flowing in a pipe.
When that water pushes through a small pipe, a toilet valve, a turbine there is pressure lost getting through those obstructions. When there is no flow through them, there is no loss.


Here's how it works on an Chrysler ignition circuit assuming no resistance in any connections or wires between devices.
Because the ballast resister and coil's primary winding are in series, the voltage in between the two is above zero but less than the voltage available (12.7 V).

Thanks all!