65 GMC voltage regulator

[finnishpetter]

Hi & thanks for accepting me as a member!

I have this problem with my external voltage regulator. I know that these issues were discussed on many other threads, but I could not solve my problem even after reading all the other posts.

Brand new battery, brand new alternator with brand new aftermarket external regulator. Using all factory connections and checked that the connectors are still wired as OEM.

When engine running the system will charge at about 13,8 volts and be just fine. When not running the battery will completely drain overnight. Went trough all normal procedures for searching the cause until noticed that pulling the voltage regulator connector stops the drainage. Checked again everything and replaced again the regulator. Same issue again. Made sure that the regulator is grounded with external ground wire. Still drains the battery.

Next step I noticed that the regulator has a bridge on post number 4 and put a pigtail on it. Measured at about 5 volts when all connected. Decided to test what happens if grounded - hallelujah - it stops draining the current from battery. Thought I´ve solved the mystery. Started the engine and checked charging - 12,5 volts - not charging. Pulled the pigtail ground on post number 4 and started charging immediately at 13,8 volts.

My question: what do i have to do to stop the drain and still get fully charging system??

[AcampoDave]

Finnishpetter, I dont know the answer, but I just wanted to let you know that there are other sub-forums on this site (i. e. electrical, engines and drivetrains etc.) You can access them by logging in and clicking the "forum jump" box at the bottom of the page. Welcome to the forum

[Pappyx3!]

Finnishpetter,

Did you get some help with this? Find the problem?

Thanks,

Papppyx4!

[finnishpetter]

Hi, no help yet with this. I´ve read all the other threads about people having issues when replacing external voltage regulators, but none of them solved my problem.

This would need someone with advanced electrical knowledge to tell me if it needs a resistor or something alike. I mean I understand that you wouldn´t normally ground anything with even low voltage, but it immediately stopped the battery drain. Also when grounded prevented the system from charging until disconnected from ground.

Beats me, hopefully someone has an answer for this.

[Pappyx3!]

Originally Posted by finnishpetter

Hi, no help yet with this. I´ve read all the other threads about people having issues when replacing external voltage regulators, but none of them solved my problem.

This would need someone with advanced electrical knowledge to tell me if it needs a resistor or something alike. I mean I understand that you wouldn´t normally ground anything with even low voltage, but it immediately stopped the battery drain. Also when grounded prevented the system from charging until disconnected from ground.

Beats me, hopefully someone has an answer for this.

Sending you a PM.

[Pappyx3!]

Does it have gauges or indicator lights?

[Pappyx3!]

Originally Posted by Pappyx3!

Does it have gauges or indicator lights?

Soon as you have an opportunity to work on the truck again, try this.

Let me know if your truck has gauges or the generator light.

1. Hook the regulator back up the way it was when it was charging. REMOVE ALL JUMPER WIRES you had added.

With a digital multimeter, Set it to DC volts, on the 20 scale

2. Record your readings with each step, so you can tell us what you read.

3. Check the output on the BAT terminal on the back on the alternator.

4. Start the truck and recheck the alternator output.

5. Once you have confirmed the truck is charging, shut the engine off and recheck it for the battery drain and record the reading.

If you still have the drain disconnect the battery. We will do some further testing to see if the alternator, regulator or if you have a wiring issue causing the problem.

Thanks,

Pappyx4!

[AngryPirate]

Kind of a long shot and may seem unrelated, but faulty horn relays will drain your battery over night too.
Just something to check.
Posted via Mobile Device

[Pappyx3!]

Any updates on what was found?

[cooperhw]

Find member VetteVet on the 67-72 threads. Electrical guru. Knows his stuff. If you read through previous posts of his I think they talk about a similar problem and how to fix it.