What makes my battery gauge read +40 and my alternator hot?

[Gary C.]

1967 427/400HP with TI, air ,etc.

After replacing the ignition/headlight harness, upon starting the car my battery gauge went to +40 and did not fluctuate, after 15 seconds or so I cut it off and the alternator was already unusually warm/hot. Something must be afoul among the alternator, regulator, starter?

I have about 13.4V across the battery and about 12.4V at the horn relay and alternator.

Any suggestions on just how to sort this out would be appreciated.

Thanks

Gary

[Joe L.]

Re: What makes my battery gauge read +40 and my alternator hot?

1967 427/400HP with TI, air ,etc.

After replacing the ignition/headlight harness, upon starting the car my battery gauge went to +40 and did not fluctuate, after 15 seconds or so I cut it off and the alternator was already unusually warm/hot. Something must be afoul among the alternator, regulator, starter?

I have about 13.4V across the battery and about 12.4V at the horn relay and alternator.

Any suggestions on just how to sort this out would be appreciated.

Thanks

Gary

Gary-------

What you describe indicates a really high current draw someplace and not necessarily a problem with the alternator or starter. In fact, after the starter starts the engine it should not be drawing any current. It sounds like the alternator is simply "responding" to the current draw so I think it's more likely the "victim" of the problem rather than the "perpetrator".

I suppose there could be a problem with the voltage regulator. I've forgotten most of the troubleshooting of these old electro-mechanical voltage regulators as I haven't had a car with one in over 40 years. Perhaps someone else can offer something on that.

[Paul Y.]

Re: What makes my battery gauge read +40 and my alternator hot?

I would check for a loose ground somewhere close to the voltage regulator or starter or alternator. It sounds like a loss of grounding somewhere. If it were a hot wire to ground you would see smoke.

[Roger O.]

Re: What makes my battery gauge read +40 and my alternator hot?

Gary,
It sounds to me like the alternator has been "told" to kick up in high gear (since your alt is hot , the ammeter is most likely not lying to you). The F terminal blue wire is sorta the throttle for the alternator and tells the alternator what to do.
Try pulling the 2 wire connector from the back of the alternator and see if the ammeter settles down.
The F terminal blue wire goes to the F terminal on the regulator.

This is where I have to stand aside and ask for some help from the old guys.
I believe applying 12 volts to the F terminal will put it in full output.

But anyway I think you could have a voltage regulator problem or a blue wire (F terminal) problem. Can't remember what happens if the voltage regulator is ungrounded ??? Hope this helps a little,if no one chimes in about the F terminal I'm sure I can find it in some of my old books.

Roger

EDIT- Yes-applying 12 volts to the F terminal kicks the alternator into full output ,( so its not like the blue wire is grounded).

[Jack H.]

Re: What makes my battery gauge read +40 and my alternator hot?

To amplify what Joe Lucia said, the high/constant charging output says your charging system 'thinks' the battery is VERY low in terms of its state of charge and is supplying at/near max output to pump the battery charge up.

That can happen in several ways:

(1) The battery truly is LOW on charge.

(2) There's a branch circuit that's 'shorted' (fully or partially) which is draining charge from the system.

(3) You have a wiring problem that results in the voltage regulator 'seeing' the battery lower than it actually is (high ohmic contact resistance, Etc.)

(4) A charging system component is defective (eg. the voltage regulator is 'fried' resulting in it telling the alternator to deliver full output current all the time).

[Donald O.]

Re: What makes my battery gauge read +40 and my alternator hot?

1967 427/400HP with TI, air ,etc.

After replacing the ignition/headlight harness, upon starting the car my battery gauge went to +40 and did not fluctuate, after 15 seconds or so I cut it off and the alternator was already unusually warm/hot. Something must be afoul among the alternator, regulator, starter?

I have about 13.4V across the battery and about 12.4V at the horn relay and alternator.

Any suggestions on just how to sort this out would be appreciated.

Thanks

Gary

You said it started when you replaced the engine bay harness, I'd start there for a short.

[Jack H.]

Re: What makes my battery gauge read +40 and my alternator hot?

Hum, there's a hint here IF we can trust the test data...

Forget about the alternator seeming to be hot for a moment (it IS bolted to the engine block...).

The data says the battery measured 13.4 VDC and the engine compartment B+ buss (side of horn relay) measured 12.4 VDC. I'll PRESUME those measurements are accurate and taken with the engine running + RPM's elevated above idle (in the +1200 RPM range).

The flag here is WHY the battery is LOW compared to normal engine operation/charging (should be in the 14 VDC range) and why the engine compartment B+ rail is a FULL one volt below the battery!

This one may be a good candidate for a qualified auto electric to look at and troubleshoot...

[Gary C.]

Re: What makes my battery gauge read +40 and my alternator hot?

thanks for the suggestions.

The problem was a loose ground. I had forgotten to tighten the starter bolt that serves the ground. Tightened the bolt and problem solved. Sign of brain rot I guess, forgetting things and all.

The voltages I reported were with the engine off. The alternator was hot to touch when the engine was not even warm, just ran for a number of seconds, not even a minute, when the battery gauge went to +40, I knew there was a problem as it never does that, at that point I was disgusted with my lack of ability and just went in the house.

I learned that a poor ground in that circuit will allow the alternator to run wild.

Now if I can just remember the lesson the next time I need to recall what I think I know.

[Roger O.]

Re: What makes my battery gauge read +40 and my alternator hot?

Glad you got to the bottom of it , grounds can cause some odd things to happen.