my truck, see sig, has a pulsing alternator.

About 2 months ago, one of the wires coming out of the alt touched the turbo when running, and shorted out, causing most of that harness to melt. i cut the harness out, and connected the big wire of the alt to the battery using 2/0 welding cable. i then installed the external voltage regulator, as described in the "sticky". I hooked it up as described, using my empty power window fuse holder to supply keyed power (i do not have power windows). everything worked fine for a while, charging right around 14v. i started the truck yesterday, and the aftermarker voltmeter that i installed showed it charging right where it should be @14v. after running for a few minutes, the guage started jumping around reading from 14-16 volts in a rythmical pattern of of about 1 second each. the interior dome light and the underhood light would get bright, then dim, in the same pattern as the guage. i checked the voltage at the battery, and was getting a steady pattern of 15.8 to 14.5, and back and forth.

can someone shed some light on what is going on here? the voltage regulator is a new one, probably 2 months old, and has probably 2 hours of running time on it. it was purchased at napa. i had the alternator tested after the fire that caused all this, and it tested fine. like i said, everything was working fine till yesterday. i am not tooo good at electrical diagnostics, so maybe some one could shed some light on this.

 

Check for AC voltage between the alternator and ground, you may have a bad diode from the short.

 

You may need a new regulator.

 

enlighten the dummy over here.......where exactly would i check, as in where do i stick the probes from the meter?? ....and i'm looking for AC voltage, not DC?

 

The regulator needs a good ground that gets to the alternator. Make sure the cab, assuming you mounted the regulator on the firewall, has a good ground to the engine.

I tend to think it's just a characteristic of this type of regulator. I had one that did it so I bought a new one and the new one did the same thing. It works by periodically stopping the field to check the battery voltage. If it is still low it turns back on and charges some more.

Mine is still pulsing but it keeps the battery up so I quit worrying about it.

Edwin

 

Mine did same to the point that people thought I wash flashing them with my headlights. I added more ground straps after cleaning all the old connections. That helped some. I also ended up cleaning a repaired inline harness fuse (not sure which one but it shuts the motor off) that had gotten corroded. That helped too. When I hooked up the rest of my Painless Wiring circuits it reduced it even more. Still a slight pulsation but not aggrivating like before. Mine is probably still a poor ground somewhere I guess since I have the internal regulator. But like he said, it charges so I quit worrying about it...

 

Stick one probe on the alt. output terminal and the other on the case. You should have less than 1 volt of AC showing. I've seen 24 volts and man did that Taurus run bad.

 

If the A-C voltage test shows no problem, stick one of those BLUE Mopar regulators on it and the pulsing will quit.

Someone more smarter than me can post the correct Mopar part number.

We just discussed all this a few weeks ago.

 

i got a new regulator, just to rule that out. i installed it, and installed a new ground from the VR case to the front clip, just as a redundant ground. it still pulses on the high side, just not as bad. i see a rythmical bounce (according to my multimeter) of 14.5v to 15.1v @the battery. the underhood light does not flash nearly as bad as it did, though, you can barley notice it. factory dash guage still bounces around in the high zone of the range on the guage.

When measued with AC volatge between the positive battery terminal and the alt case, i see a pretty steady 27.1v. I am guessing that is not right.

i think i have the grounds covered. 2/0 from battery to engine, 2ga from batt to front clip, 4ga from front clip to VR case. i cleaned all connections, and sanded paint to bare metal.

 

Yeah, it sounds like one of the diodes in the rectifier is blown.

 

does one install a new diode, and if so how? or a new alternator? i found a source online for a new alterntor for $100

 

That's a smokin' deal. Are you sure it's the right alternator?

If you have an alternator/starter rebuild shop near you they might be willing to sell you a diode trio and you can swap it yourself. If you go this way, get new brushes too.

 

hmmm, i guess i read it wrong, but its still a new, nippondenso 120amp for $137, not 100. i think that is the way i am gonna go. Thanks for your help.