12si conversion-- now overcharging

[lowlyfec10]

69 c10 with ammeter. did the harness mod per mr.Vettevet's PM and history of responses in past threads. ive searched thru and thru for an answer before i felt the post. i just swapped the altnernator out for another from O'smileys...same thing....runs up to around 15.5x volts...didnt care to watch it creep any higher. i have continuity to ground. one wire gets 12v constant....the other gets 12v with ign on and nothing with it off....correct as i have seen in past searched threads. i replaced my fusible link since it was burned up......no difference. i have new battery and ground cables and optima battery. and i have the hei conversion if it makes any difference. im just baffled as my remote sensing wire has the power when/where it needs it...but im getting results as if i dont have it -_-

[gmachinz]

Are you reading 15.5V on a volt gauge or actually measuring it off the alt. charge post with a voltmeter.

[lowlyfec10]

This is at the battery posts with my bluepoint multimeter

[RichardJ]

Don't check grounds with an ohm meter (continuity). The ohm meter tests with 1 or 2 , 1.5volt battery(s) at very low current.

With engine running, connect one meter lead to the battery Neg post. With the other lead, check for 0.0volts (or very near to that) on the engine block, frame or anything you expect to be grounded to the battery.

[lowlyfec10]

I get .001v if i check it that way between post and the alt bracket that the ground wire attaches to

[RichardJ]

>> between post and the alt bracket that the ground wire attaches to <<

What is voltage battery Neg post to truck frame? Engine running.

>>one wire gets 12v constant....the other gets 12v with ign on and nothing with it off<<

Those are #2 and #1 pins, respectively, on the Alternator?

Using the same ground at the battery for your meter, and the battery voltage is still 15.5V, what is voltage at the BAT post on the alternator?

What mods did mr.Vettevet's have you make?

[lowlyfec10]

1. it shows around -0.0016v or so when i go from neg post to frame.

2. yes, red to blue...constant 12v at terminal 2. brown to white has power with ign on and nothing with ign off...at terminal 1.

3. while running, battery posts measure 15.7ish and seem to settle there.....at the alternator post it is 15.9ish.

4. he is trying to help diagnose as well, but my wiring seems to be correct as i've checked and rechecked multiple times and tried the wiring at the alternator in other alternator ways with the same results.

5. still stumped.....try a 3rd alternator? was thinking of trying the 78amp 12si and hope for the best.... -_____-

[lowlyfec10]

also, my alternator has that R terminal with a smooth stud protruding and covered by a rubber cap...not sure if that makes any difference.....??

[lowlyfec10]

Welp...i swapped out for a 78a version 12si alternator. No change really...seems to be steady at 15.3x volts now. No diff if the lights are on. Im beyond lost now..... :/

[68c10airstream]

Hi lowlyfec10, If my memory is correct the voltage regulator is in the rear half of the alt. body. Do a voltage drop between the back half and the neg. battery terminal. Another words use a voltmeter to parallel this circuit. Touch one lead on bat. neg. terminal, scratch the rear alt. body bare and touch that area with the other volt meter lead. If it shows more than about .2 volts start cleaning alt body, alt bracket to engine etc, etc. Living up north as a dealer mechanic in the salt belt i fixed a few for an overcharging issue by cleaning alt. brackets and alt bodies. Good luck, Brian Fuller

[lowlyfec10]

Thanks for the input sir. As minimal as my grounds are at the moment...they are sufficient but i do plan on running all new thick grounds for every needed connection that came from the factory...if not more. But i noticed the voltage reading on my multimeter slowly creeping up on the battery terminals.....with the ign off -_- turns out my bluepoint multimeter is malfunctioning all of a sudden. So i hooked up the volt gauge inside the truck (sunpro 3 gauge set) and boom....14v at idle. I will borrow a friends dvom to confirm but i think my expensive multimeter hates me. :/

[VetteVet]

Here are the pictures of the original alternator and the 12 SI with the connections to convert to it from the original.



The 12 SI



How to convert.