Vehicle: 1976 D100
Electrical system is still all stock.

I had this truck for a few years and the charging system was fine, other than the typical dim dash lights due to voltage drop through the system. Lasst year I swapped out the newer chrome voltage regulator with a NOS Mopar voltage regulator. I also installed a grpound loop between the case of the alternator, the voltage regulator, and the negative battery terminal.

A few months ago I finally installed a voltmeter. To my surprise, the voltmeter showed the alternator putting out 14.5-15 volts at all times the engine was running, except for some odd instances where the engine was idling slow and the output dropped to around 11.5-12. But about 98% of the time the voltmeter showed 14.5-15 volts.

Last week I got in the truck to run some errands and I saw the ammeter showed discharge and the voltmeter was reading close to 10 volts with the engine running. The night before everything had been fine. Using a hand-held voltmeter, I double checked the voltage at the output terminal on the alternator and at the + terminal of the battery. Both showed 11.2 with the engine running.

I changed alternators and no difference. I checked all connections and they are good.

I know I have about a 2 volt drop across the ignition switch, but I am fairly certain that is not the cause of the no-charge problem.

Could this non-charging problem be related to a failed ammeter? When time allows I fully intend to bypass the full-flow ammeter on this truck, but it is still hooked up for now and it appeared to be working fine.

Next on the list of things to do is swap out the NOS voltage regulator with another one, but could my no-charge problem be caused by the ammeter? All electrical devices work fine, the battery just isn't being charged.

Any constructive input is appreciated.

If the ammeter is showing a discharge, it's not dead; current is going thru it (although in the wrong direction).

If the ammeter wasn't passing any current thru it, it would be showing zero.

Sounds more like a voltage regulator problem.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

OK, thanks. That would be disappointing since it is a NOS unit,but I guess it has sat on the shelf for about 40 years. Not surprising if it failed.

D

I had a 79 ramcharger that I installed the 100a alternator Left over from the cordoba that I had owned before the ramcharger. Worked GREAT until one day a few months later I went to jump a dead car with my ramcharger, and that alternator went full tilt. I was standing between my truck and the dead car, I happened to look towards my truck and I could see a plume of smoke from within, thru the windshield. I thought my whole truck was going to burn down. I had gotten the dead car started, and was unhooking the cables as I saw what I did, I discovered that the ammeter had let it's smoke out and I had a blob in the dash where it had been. I wound up buying a stewart warner -100-0-+100 ammeter and putting it in the new hole that I had created in the dash.

The connections inside voltage regulator connector they have split apart https://www.rockauto.com/en/moreinfo.ph ... 55&jsn=431

Got it. I will dig through my stash and see if I have any more VRs I pulled from parts cars over the years, and then hit up my local parts store and hope the new VR works.

Matv91 gets the prize. Connection was loose or not good. Wiggling the plug fixed it.

Good to hear you found the problem.

Related question: Is it normal for the alternator to be putting out 15 volts with a healthy VR?

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Could be, depends on battery condition and such, would be the absolute highest I would want to see. 13.5- 14.7 would be the typical expected range.

Stupid double post deleted.

I think the alternator is putting out more volts than desireable, but the battery in the truck is old and flakey. I uspect a newer battery in better condition would let the charging system op[erate closer to 14.5 volts. I should replace the battery but have other things to take care of first. As long a it holds enough of a charge to start the truck and lets the engine run, I will keep running it.

15 isn't overly frightening, but much higher and bad things await.

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Official Cookie and Mater Tormentor.

I chased a high voltage issue for weeks. Turned out the newer Voltage Regulator from Rockauto, Standard Motor Products (VR125???), was faulty from the get-go. Ordered a stock looking one from ebay and all is well. 13.5-14.5 volts all day long.

The charging system on this truck has put out 15 volts both with a new no-name chrome VR and a 40+ year old NOS Mopar unit. I believe the problem lies somewhere other than the VR.