M35 60 AMP Altenator troubles...HELP!

[Rickyoday]

I sold my 1970 AM General M35A2 and a few days before pick up by it's new owner, the voltage regulator decides to start charging the batteries at around 75 volts. I bought a new regulator from Memphis Equip. matched to my Prestolite by serial #, installed it yesterday, and now it's charging at 35 volts. What am I missing? I tried using the adjustment screw, with no noticeable change in voltage. Did I get a bad voltage regulator, or is the altenator the problem? I charged both 2 year old batteries prior to the new regulator purchase, both also load tested fine. I sold the new owner the manuals for the truck, so I don't have them for reference.
Any help would be appreciated.
Thanks,
Rick

 

[cranetruck]

Check the cable from the regulator to the generator, you may have a broken wire within it, more specifically,the wire which controls the field current.

 

[Rickyoday]

Check the cable from the regulator to the generator, you may have a broken wire within it, more specifically,the wire which controls the field current.

Hi Bjorn,
Thanks for your reply. The altenator I have has the "built in" voltage regulator, that has a ground, hot wire, and small 14 gauge(?) wire with the rubber waterproof connector. Is that what you were referring to?
Thanks,
Rick

 

[m-35tom]

small wire simply tells it to charge, everything else is inside the alt end housing.

 

[cranetruck]

Rick, when you stated that you had a "new regulator from Memphis", I assumed that you had the original generator (external) regulator set-up. Sorry.
The "waterproof connector" needs to be wired via your accessory switch, so that it's 24vdc for your alternator to produce an output, it's like an enable input IIRC.
Yeah, make sure the alternator is grounded properly too.

 

[acetomatoco]

Make sure you don't have a bad battery with an internal short.. makes it difficult for the voltage regulator to decide what to do...

 

[bottleworks]

Is the feed from the accessory switch (ref as the waterproof connector) dropping voltage with the engine running and alternator charging? If that feed isn't providing correct voltage to the regulator, the regulator will believe the batteries/charging system is under high demand and produce a higher charging voltage.

You have to check for voltage drop under load...ie don't disconnect the wire.

 

[Rickyoday]

Thanks for the suggestions! One of the batteries is bad, so I will be getting 2 new batteries delivered tomorrow. Bjorn, I will check for voltage drop as you suggest, if the new batteries don't clear up the problem. I'll let you know what happens. Thanks again guys!

 

[ARMYMAN30YearsPlus]

Welcome to Steel Soldiers that is a good looking Suburban you have there. How far are you from the Maryland line? There are lots of great threads to read on all types of military vehicles so I hope you have time to come back time after time like many of us do. My Alternator was doing some crazy things just before I deployed and I hope my boys are keeping the batteries charged and starting it once a month or more.

 

[Rickyoday]

Hi David,
Thanks for your compliment on the Suburban! I'm about 35 minutes from the Maryland line, NE of Rising Sun.
After talking to a mechanic from Memphis Equip, I finally figured out that one of the fields in the alternator was bad, and got a re-manufactured alternator from them. End of problem!
Thanks to all the members who responded to my call for help!
Rick