Alternator or wiring?

[danielb927]

Last few trips in my car, the ammeter shows fluctuation between charging/discharging of the battery. It's not ever in the middle, just flip-flops between -15 and + something. Initially it only occurred as I let off the throttle and stopped at an intersection, lately it's discharging at cruise as well. Seems to generally come back to charging when I'm stopped and in park. To those of you who have been around these cars longer than I have, do failing alternators ever have this kind of behavior? Or does it sound more like a problem in the wiring somewhere?

 

[67Dart273]

This could be a few things

1.......Back in my wilder days, I had this happen (did this to) at least two Mopar alternators. Run the engine in darkness, raise the hood, and rev the engine up while watching the alternator. Now you must separate whether you are seeing slip ring sparking or "something else." If what you see is lots and lots of miniature sparks that seem to be out in the stator area, then what has happened is, the stator windings are loose, rubbing, and wearing the insulation off between turns

2.....Even if you have to run temporary wiring make some running tests. Monitor battery voltage and alternator output stud voltage and see if you can see voltage change at the time that the ammeter acts up. ONE VERY GOOD way to do this is to hook one probe to the alternator stud, and the other probe to the start relay stud. This gives you an "end to end" voltage drop from the alternator, through the bulkhead, through the ammeter, back out through the bulkhead, and to the battery.

3...Might be the ammeter itself or the connections to it, including the eyelet wire ends themselves. MORE LIKELY this is the connections in the bulkhead

4...IN RARE but has happened, the "welded splice" in the ammeter circuit may have failed. This is a factory welded splice a few inches from the ammeter in the black ammeter wire. You have to pull the cluster and untape the harness to inspect it. "Save it" for last, LOL

5...READ if you have not already, this excellent article

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

 

[danielb927]

Went out to check some connections. The green field wire on the alternator was very loose and pulled right out of its spade connector. So, I'll start by replacing that and then see if the problem persists.

Thanks for the detailed rundown, 67. I had seen that article but it's been a while. The ammeter bypass is on my list as the car, when I got it, already had a burned-out connection replaced elsewhere on the charging circuit under the hood.

 

[67Dart273]

I would almost bet you've found the problem

On a side note, a friend with a 68 RR had a similar problem way back in the early 70's. This was my Navy days at Miramar. I ran it down eventually to the welded splice. There we were, he thinking / wondering if I was insane, tearing his dash apart, untaping the harness.......until we found it!!!!!!!!!!!!

That was the very first failed splice I found, and have been a party to some 8 since, in one form or another. This of course, was way WAY before Al Gore invented the internet, LOL

At the time, all I had to go on was my 69 (I had owned) and my 70 RR service manuals.

 

[danielb927]

Replaced that terminal and it did the trick - charges much faster now and no fluctuation anymore. Probably did the damage a month or two ago when I was trying to tighten up the alt. belt and it's been vibrating out of the fitting since then. Thanks for the help - glad I didn't have to get to looking at that splice! Worst electrical gremlin I've had was a gauge cluster screw that had pierced the wiring harness above the gauges, I had to start the car by shorting the relay with a screwdriver for a month or two until I found that one.

 

[67Dart273]

Very good. Easy fixes are always the best ones. LOL