[bhill86]

Recently, after changing my drivers side header gasket on my 77 T/A I noticed my alternator seems to be overcharging based on my factory gauge and I also have a USB outlet that I replaced my cigarette lighter with and that has a digital readout showing the volts. At times, it’s as high as 15.1v but it seems to be intermittent.

I found the sensing wire terminal on the alternator plug was dislodged so I thought that was it. Fixed it and voltage went down to 14 but on my way back home, at relatively low RPM (1500ish) I was back up around 15v. At idle, when it seems to be acting up, I’ll be at like 14.6. When it seems to not be acting up I’ll be around 14v at idle.

The only wiring I touched during the gasket change was dropping the starter and removing the wires to it.

Am I looking at something as simple as the regulator in the alternator going bad or should I start somewhere else? Alternator is probably less than 4-5 years old and same with the battery. That might only be 2-3.

[johnta1]

I'd check the voltage at the battery itself and see what it is?

The wire to the starter and to the alternator (from starter) may be loose or not good connection. The alternator is seeing that it needs to charge but the voltage isn't going to battery completely?

Anyways, check the connections.

[bhill86]

Ok I’ll start there. Thanks.

[padgett]

Sounds like a regulator issue. Easy swap just make sure you mark the clocking of the halfs.

[bhill86]

Originally Posted by padgett

Sounds like a regulator issue. Easy swap just make sure you mark the clocking of the halfs.

I’m not sure what that means exactly. Is that for vehicles with an external regulator? My 77 doesn’t have an external regulator.

[stellar]

It means when you separate the alternator halfs to be sure they go back together in the position they came apart. Clocking position is when you are looking at the back of the alt, the reg plug can be in four clock positions relative to the adjustment bolt on the front half. If the reg plug is in line with the adjustment bolt ear it is at 12 O'clock 90 degrees to the right is 3 o"clock, reg plug at pivot bolt is 6 o"clock. Yes 1977 is an internal reg, but clock position is relevant to either internal or external alt.

[bhill86]

Originally Posted by stellar

It means when you separate the alternator halfs to be sure they go back together in the position they came apart. Clocking position is when you are looking at the back of the alt, the reg plug can be in four clock positions relative to the adjustment bolt on the front half. If the reg plug is in line with the adjustment bolt ear it is at 12 O'clock 90 degrees to the right is 3 o"clock, reg plug at pivot bolt is 6 o"clock. Yes 1977 is an internal reg, but clock position is relevant to either internal or external alt.

Ok thanks. Makes sense. Learned something new.

[stellar]

There are a few things that can cause an overcharge. Bad regulator, low volts at sense wire, bad ground, bad battery. An intermittant overcharge is usually the regulator. Check connections first.

[bhill86]

Originally Posted by stellar

There are a few things that can cause an overcharge. Bad regulator, low volts at sense wire, bad ground, bad battery. An intermittant overcharge is usually the regulator. Check connections first.

Will do. Thank you

[OG68]

My money (what's left of it anyway) is on the starter wiring. Worked fine until it was disconnected. May be slightly loose with an intermittent connection.

[bhill86]

Not that I’m opposed to checking the wiring at the starter, I just won’t get to it for a few days likely, but I can’t help but wonder how it might have an effect on my issue. From memory, and my wiring diagram, I only have 2 wires to the starter: the fat cable from the battery to the main terminal on the starter and the purple “start” wire from the ignition switch to the “s” terminal.

[bhill86]

Got some time tonight and climbed under. Only the positive battery cable goes to the large starter terminal and the small wire to the “s” terminal. Removed them and cleaned them anyway while I was there.

I did have a thought which concerned my negative cable to the engine. I removed that for the gasket change so I took a look today and they could’ve used a good cleaning which I did. Could that have caused enough resistance to “trick” the sensing wire on the alternator to overcharge? Either way I cleaned them and also double checked the terminals on the alternator output post. It’s raining here so no test today.

I don’t have a good multimeter at the moment so one with an needle is all I had. Battery showed ~12v so I put a charger on it for a bit. It showed just over by the time I was done.

I’ll test drive tomorrow if I have time and can maybe borrow a better multimeter.

[stellar]

I doubt if it was either of them. You probably would have had a starting problem if either of those were bad. Double check the sense wire connection, since that was a problem at the beginning. Other than that I woul dorp a new regulator in the alt.

[bhill86]

I actually did have a weak start issue but I wasn’t sure if it was related or just from a weak or damaged battery.

I did go for a 15 minute drive today and my initial startup sounded strong and I maintained charging at 12.3-12.4v the entire time regardless of rpm so I’m thinking that may have done it. Hope so. Easy fix if so. I guess some time will tell.

Thanks for everyone’s input as always.

[Bill Hanlon]

If the voltmeter is reading correctly (12.4v regardless of RPM) the system is not putting out the correct voltage. Should be 13 + volts.

[bhill86]

Sorry, I meant 14.3-14.4v.

[Bill Hanlon]

I went back and re-read the posts in this thread and didn't see this listed, so you might want to give it a try.

Remove the sense wire from the alternator. Make up a short wire from the sense pin on the alternator to the big terminal on the back of the alternator.

Crank the engine up and check the alternator output again.

If the voltage is still too high (14.3+ volts), turn the engine off and re-connect the sense wire back to the factory configuration. The sense circuit is OK.

IF (big if) the voltage is down in the 13v range, the problem is low voltage (too much resistance) in the sense circuit.

[bhill86]

I went for a long drive today and stayed at 14.2v. No starting issues at any point. I think I’m good unless anyone has anything else to add.

I didn’t try the advice above. Still think I should or leave well enough alone? Thanks.

[johnta1]

Yes.

[bhill86]

Yes what, try the sensing wire truck above? Do you think my voltage is still out of line at 14.2v?