Dual Alternators - Or adding one I should Say.

[wirewrangler]

Hi Everybody!

Thought I'd post up what I found adding a second alternator to my truck for posterity I guess.

I recently added an alternator to my 2003 GMC Sierra 3500 and I only connected 1 wire from the driver side alternator to the ECM. I connected the third terminal over from the left (looking at it from the front of the truck and the same pin as the brown wire on the pass side alternator) to the Blue ECM connector Pin 32 with a piece of 18awg TFFN wire; it's what I had. If you wanted it to match what my sources tell me, make it a brown wire and judging by the size of the little crimps, it ought to be a 20awg or a 22awg, I'd go with 20...

When I fired it up, it started working. I know this because I unplugged the control from the passenger side alternator with the engine running - I got the battery light but the charging voltage was still at 14V on the gauge. I opened the circuit breaker on driver side alternator, and the voltage dropped on the gauge.

FWIW, I'm running dual 145 AC Delco Alternators. Bought the bracket, bolts, plug, and ECM terminals through GM Parts Prime or one similar. I bought a 150A circuit breaker off of amazon and wired the main through that where the pass alternator connects to the batteries in the little red flip open doo dad. I used #2 awg welding cable and crimps.

Below is what I bought and it all worked out with extra parts left over! I through a Goodyear 1061370 / 6PK3480 but it's squeaking / slipping and I need to find a better one. And keep in mind, I think if you're going to run dual 105A, the belt is a tad shorter.

Hope this helps anyone looking to do this.

11516360​

BOLT,A/C CMPR UPR FRT BRKT​

97356246​

BRACKET-GEN​

98057284​

PULLEY-DRV BELT IDLER​

11515769​

BOLT-METRIC HEAVY HEX FLANGE HEAD REDUCE​

15306329​

CONNECTOR-W/LEADS, 2-WAY F. *BEIGE *MATH DATA​

12084913​

TERMINAL,WRG FEMALE MIC/P 100/W(20-22 GA)​

 

[wirewrangler]

Here's the circuit breaker I used.

 

[MrMarty51]

Any pics of the alternators set up on the truck ?
About how much did You have into the entire setup ?

 

[wirewrangler]

The AC Delco alternator 321-2128 was $262 no core charge on Amazon.

GM parts prime for the rest:
$16.36 for the bracket
$15.35 for the pulley
$5.54 for 2ea bolts 11515769
$18.11 for the connector 15306329
$2.00 for a five pack of terminals
$15.60 for a five pack bolts 11516360View attachment 75057

I'm planning to do something more permanent with the control wiring. I'd really like to run it through the bale connector but I don't think it's worth the trouble. I also need to remove a little more material off of the red door to get around the cable I added.

 

[WarWagon]

Here's the circuit breaker I used.

Nice install.

Curious why a breaker on the output of an alternator? Vs a fuse or fusible link?

I would insulate every one of the exposed hot connections otherwise I would be seeing sparks with setting tools and parts on them the time.

 

[wirewrangler]

I can clear the fault and reset a circuit breaker as opposed to going and finding / purchasing a fuse. Also, for testing, I can push the button and disconnect the alternator; use it for a handy switch. I'm going to do the same thing to the passenger side alternator. I ran out talent trying to think of where to put two breakers side by side and gave up at the time.

I'd like a little more insulation on those connections myself - just went poking around and found these - https://www.amazon.com/STC10-8-Sili...359124&sprefix=2+awg+terminal+,aps,169&sr=8-4 - who knew!

 

[MrMarty51]

I can clear the fault and reset a circuit breaker as opposed to going and finding / purchasing a fuse. Also, for testing, I can push the button and disconnect the alternator; use it for a handy switch. I'm going to do the same thing to the passenger side alternator. I ran out talent trying to think of where to put two breakers side by side and gave up at the time.

I'd like a little more insulation on those connections myself - just went poking around and found these - https://www.amazon.com/STC10-8-Silicone-Terminal-Alternator-Junction/dp/B08RJ4Z9G6/ref=sr_1_4?crid=1GEMTNE47TO7M&keywords=2+awg+terminal+protector&qid=1654359124&sprefix=2+awg+terminal+,aps,169&sr=8-4 - who knew!

Some of the GM alternators came with a similar alternator battery wire terminal protector. I dont remember if they had a cap over the end of it. Seems that they didnt. It took a socket to get into it to get the nut loose.

 

[WarWagon]

Also, for testing, I can push the button and disconnect the alternator; use it for a handy switch.

Generally a fault on this wire requires finding the problem and should be very very rare. Diodes shorting in the alternator is the common problem. Failure to open with a shorted condition means a vehicle fire period. A fusible link in addition to the breaker could reduce risk. (Larger amp on fusible link than breaker of course.)

Be careful using it like a switch. Using this breaker to shut down or connect a running alternator is a bad idea. The field is still energized so the unloaded voltage will spike. With remote regulator sensing the voltage can stay high. Hopefully the diodes etc. in the alternator side will take it. Closing the breaker can voltage spike an expensive ECM before the electronics respond and field strength can fall off.

 

[Will L.]

Keep in mind folks that he is an electrician. So he is wiring it like any other electrical circuit is normally done, not like a’car. It is a smarter way to do it- but automotive does things low cost. This way is more expensive and when there is an issue an automotive tech is gonna get confused, but any electrician is gonna love it.
Having earned my paycheck from both sides- I like how he did it. I wouldn’t be surprised or upset if he added a second one from the factory alternator.

Simply an expense that does the same task as a fuse- just does it better and should never need replacement.