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Alternator Help

Posted: Sun Jul 04, 2021 11:02 pm
by AppleTech
Sorry for the long write-up here, I want to be clear on my issue as I solicit advice :)

1975 TGB 11 (24v) with stock alternator (external regulator in cab)

- Today, charge light came on during normal driving - started to flutter out at higher revs but was not staying out during normal driving (which is abnormal for my truck).

- When I got home, I checked the batteries - 24.98V there - no change in voltage when revving engine.
- Voltage went up slightly when engine was turned off, a hair over 25v
- Crawled under the truck, noticed the ground wire going from the alternator was frefloating - reattached to intake stud
- Restart truck, no apparent change in voltage when engine revving, charge light still on during most of RPM band
- Decide to remove alternator connections and clean up any dirt/corrosion.
- Larger center post on the heatsink-type part with 3 posts started spinning
- Removed that part and then removed the post, but noticed there is a wire bit from the center of the unit that was hooked to that post but now broken - not sure how it is supposed to connect.
- Reassembled that part, tried to have the little connector get contact with the center stud when tightened down
- With that unit back on the alternator and everything hooked up, I'm not getting charge lamp in "on" or when the truck is running
- Voltage still hanging around 24.98v at the batteries and no change related to RPM

So I think I have a compound issue in that either my voltage regulator is problematic, or the alternator itself is broken. AND I think I broke that little connector on the center stud of the heatsink unit - I'm not sure how it is supposed to connect... part diagrams not helpful.

Ultimately, I think I'm going to end up ordering a modern internally-regulated alternator but it would be nice to fix this unit... any thoughts on my predicament? If I switch to a modern alternator, can I still use the charge lamp system or do I need to wire up a voltmeter to the dash?


Re: Alternator Help

Posted: Mon Jul 05, 2021 11:15 am
by Jim Molloy
I cannot help with your wiring issue with the original Marchall S.E.V. unit. I cannot get our local HIGHLY respected NAPA electrical shop to do anything either.

Over the years, I have had my fair share of Marchall product failures. The most recent was the failure of the voltage regulator leading to unrestricted overcharging of the batteries. That was an easy (replacement Bosch VR from Tatanka) but expense (two swollen/destroyed batteries requiring replacement). I am still running the Marchall alternator in that truck but have a 24V GM/Delco "one wire" internally regulated alternator sitting on the shelf...waiting.

I have had the opportunity to install the 24V Delco units on two other Volvo TGB trucks we have owned. In both cases, the charge indicator light is not functional. We installed VDO voltage gauges to monitor charge function status. Now, the the availability of the small combined USB charge port/volt meter that plug into the dash 24V access, monitoring is simple.

Best wishes for a speedy resolution to your issues.
Jim Molloy

Re: Alternator Help

Posted: Mon Jul 05, 2021 12:52 pm
by AppleTech
Jim - can you dig up the part numbers on the Declo units you used? I am at the point now where I just want to purchase an upgraded replacement but I'm having trouble finding the correct unit from the list I have... all options coming up are shipping from overseas. Hoping the Delco units you like are available stateside...

Also I think I sent you a message on Facebook requesting same (from Charles F., my FB account) but it likely went to your "unknown senders" folder, so please excuse the duplicate request!


Re: Alternator Help

Posted: Wed Jul 07, 2021 10:30 am
by Jim Molloy
Two years ago tomorrow, I purchased P/N SE24V from Rareelctrical in Morrisville, NC. Their description on the invoice is " New alternator fits 10SI Delco 1 wire self e". I paid just under $105 USD. Outside diameter of the body is 5.5". The only stamped number on the forward housing is BT18J3. Their website is:

Hope this helps.

Re: Alternator Help

Posted: Wed Jul 07, 2021 4:16 pm
by AppleTech
Thanks Jim you are awesome!!!