My Superburban has been burning up voltage regulators in the alternator faster than I can replace them. The voltage pegs out when I am at highway speeds, but goes back down to ~14V when at idle. I have 2 Optima Redtops that I would hate to fry because of a stupid wiring issue, so I took a closer look to make sure that everything was good. This is what I found:

The supply for the fuseblock positive comes directly from the alternator's large lug. Then, there is a wire from the large lug directly to the passenger battery positive post. Now, I had understood that it was better to have both the supplies for the fuseblock and the alternator's large lug coming directly from the battery and joining at the big fuse thinger on the firewall. They would all be connected to the same exact circuit either way, but the original way would help to prevent the voltage regulator from going nutzo and cause the alt. overcharge the batteries.

Can someone take a look at their setup and let me know how the acc. wire from the battery connects to the firewall-fuse-thinger?

Or, possibly, my wiring is A.O.K., but I just have bad luck with voltage regulators.

Hm, I have two wires on the output terminal of the alternator. One goes to the battery on the passenger side, the other one seems to disappear in the wiring harness. There is something that is probably a fusible link on the firewall, towards the drivers side. That`s probably the same as what you have.

What comes to mind is the other three wires going to the alternator. Afair, one of them is for the battery-charge light, the other one supplies the voltage regulator, and I think the third one provides a ground connection. If there`s a problem with the supply for the voltage regulator, that might result in setting the output voltage too high and thus frying the regulator. 14.8V is about the highest output voltage you should ever see.

Another possibility, though unlikely, is having no load on the alternator at all. That would create spikes of very high voltage which can damage the alternator.

I`d probably check the three "control wires". If they are ok, I`d have the batteries tested with a battery tester and have the actual output of the alternator (when in the truck) tested as well.

My Superburban has been burning up voltage regulators in the alternator faster than I can replace them. The voltage pegs out when I am at highway speeds, but goes back down to ~14V when at idle. I have 2 Optima Redtops that I would hate to fry because of a stupid wiring issue, so I took a closer look to make sure that everything was good. This is what I found:


I don't believe there is anything you could do in the wiring to make the internal regulator burn out. The alternator and regulator is a self-contained charging system and only has three connections. The big post must be hooked to the positive battery one way or the other. In regard to the plug-in harness with two small wires - one supplies field current to get the alternator to start charging when you first start the engine ( #1 terminal), and the other is a battery-voltage sensor (#2 terminal). Since your batteries are only capable of making 12 volts - assuming you've got them hooked up correctly in parallel - there isn't any external voltage available higher than 12-13 volts no matter what you do. With a system working correctly -all three terminals will be around 14 volts when the engine is running and charging correctly. If it is higher - you've got some sort of problem inside the alternator - maybe even a grounded regulator over-ride lug. The alternator has a little port-hole on the back to test the regulator. If you stick a piece of metal in there - and ground the metal tab inside - it makes the regulator put out full output. If that is somehow grounding all the time - it could cause your problem.

So, it looks like I am just unlucky!

Well, if the battery voltage sensor senses the battery voltage incorrectly, the alternator may be regulated to put out a higher voltage than it should.

If I understand it correctly, the alternator is regulated in such a way that it increases its output (amperage, not voltage) when more power is drawn from the system (amperage). An increase in demand is detected by a drop in voltage.

Now if the alternator sees a drop in voltage due to faulty wiring and increases its output, the voltage in the system will get too high.

So you need to check the wiring of the plug-in harness.

Well, if the battery voltage sensor senses the battery voltage incorrectly, the alternator may be regulated to put out a higher voltage than it should.

If I understand it correctly, the alternator is regulated in such a way that it increases its output (amperage, not voltage) when more power is drawn from the system (amperage). An increase in demand is detected by a drop in voltage.

Now if the alternator sees a drop in voltage due to faulty wiring and increases its output, the voltage in the system will get too high.

So you need to check the wiring of the plug-in harness.

That's why I mentioned what the voltage should be on all three connections. If he wants to check for a poor #2 sensor connection - all he has to do is jump a wire between #2 terminal to the output post on the back of the alternator. On many applications, that's the way is wired anyway.

All of my alt. wires tie together down at the starter I suppose this is the connection to the batteries. My rig is a conversion from a 350 thou. I go through alternators about 1 a month.

I have taken to running with the lights on no matter what time of day to keep the voltage down to about 15V.

what does a test volt meter read . sorry if i missed it in a prevous post. mine in my chev reads high on the gauge but ok by a test meter.

The issue only shows up at high RPMs, so I have not tested while the problem shows up.