Alright ladies and gentleman, this may be my first post but I’ve been using these forums for the past 3 years since I got my rig. So thanks in advance for all your insight. Sorry if this post is a little lengthy I’m trying to be detailed for you guys. Pretty much everything I’ve tackled on my own from replacing a cracked exhaust manifold to going through 2 batteries and 2 starters in the span of a few days because my solenoid kept frying everything (then I did the PMGR starter upgrade thank the lord).

Anyway as the title states this is a problem with a 3G upgrade.

My vehicle is a 1989 E250 Club Wagon Coachmen Class B Conversion Van 5.8/C6 with not even 110k miles yet.

I decided to do the upgrade not because I was having problems, but because I am going to use an inverter and solar panels down the road and the higher amperage alternator over the factory 1G would ideally provide a bit more charging towards the House Battery system, since my 1G 100 amp was running everything smoothly already.

Sizing was an initial issue. I had measured my factory 1G - 8.25 inch ears, alright go to O’reilleys to warranty out my 1G and I get my 3G large ear off a 94 4.9 engine. I went to slap that bad boy in and the ears are almost an inch too thick for the top mount hole, forcing you to grind down the alternator ear itself. Seems sketchy, but I did it anyway. That thing did not seem safe bolted up with barely half an inch holding that alternator ear on. I wondered what I was doing wrong for a day or two before I got the bright idea to find a different alternator bracket from a pull yard.

I found a 91 Bronco with the 351. Perfect! Same alternator bracket EXCEPT it’s 7 inches, and where the tensioner sits and the flange comes over to the alternator ear, it’s actually curved a bit inwards so the alternator would just slide over to it when pivoted. Indeed what I needed, and I knew I needed a smaller case alternator now.

Back to Oreilleys, I didn’t let them see how I murdered their alternator and they let me swap for a 99 v6 mustang 130 amp. Great, so I had to clock it and brought it to my local alternator shop. He clocked it for me and tested it for voltage and it “Worked great” he said.

Back to the van, I ground down the alternator bracket like everyone does for their 3G. Test fit- perfect. I reassemble everything to make sure the bracket is lined up nicely, and checked where pulleys sat now as opposed to with my slightly larger original bracket. Used original belt and it seemed a little tighter than previously given the half inch larger alternator pulley most likely

Alternator installed, wired as follows:

4G wire from charge stud to 175amp megafuse to starter solenoid hot side

D-plug: g/r to original g/r from original external voltage regulator that runs to a connector and to fuel injection wiring area on passenger fenderwell

Yellow 12g wire to starter solenoid hot

White wire to alternator plug

Put my yellow top 34/78 back in with 12.5 volts

Start her up...

Only 12V at the battery...

Turned on every single load possible, 11.5V???

Now when I was having battery issues a year ago I also changed to the 100amp external 1G alternator. It was late and I actually snipped the whole black/Orange charge wire assembly from the alt to the solenoid to replace it with a 4G. Well on the van, and not other vehicles I’ve noticed, there’s maybe 5 wires that are tied completely into the main alternator harness that power the vehicle and the fuel injection system. I remember using a small power converter in my Prius to run a soldering iron to crudely re-attach a few wires to the 4G. It was 2 maybe 10 gauge yellow wires that go to a connector on the pass fenderwell, then a blue wire from the external regulator, and then a small yellow/white wire that ran next to the green/red wire (which I thought was my ammeter line and alternator signal) also fed right to that line. All of these wires I have a ring terminal end on now and are on the HOT side of the solenoid. The factory regulator had the green/red, an orange that went to the 1G alternator plug, and a blue that went to that main line.

So how am I not getting 14V here?

I re-used the green/red signal wire from my factory external regulator..I’m about to check and make sure that’s 12V when the key is on.

And the yellow wire goes right to the starter solenoid so it obviously gets the voltage. That is exactly the same as the battery when tested with my MM.

Could the white plug be faulty? Could my D plug be faulty? I actually took both off a 2000 mustang at the pull yard the same day I got my alternator bracket. The white wire plug actually has a broken lock mechanism but I checked to make sure it was tight for testing purposes. There is a bit of a belt squeal when I step on the gas, I thought that might have to do with the alternator creating more resistance if it’s not charging properly or overcharging. If I can get 14V I was gonna see if the squeal dissipated and if not I would try a new belt and then try warranting out my 6 month old Gates tensioner, and if that didn’t help I might go a bit larger of a belt due to the larger pulley diameter.

I’m frustrated because the wiring seems very straightforward. Unless something is wrong with the green signal wire it should be working properly, everything else is bulletproof. Unless the lack of voltage has to do with the bracket change and belt combination? It’s hard to tell. I’d figure if the pulley was too big I’d get maybe 13.5 instead of 14.5 but not just a no charge condition. I also made SURE I had shiny metal on my block before installing the bracket, and confirmed every bolt hole was pure metal before assembly. I even added a 4G ground wire to that rear threaded hole in the alternator case and ran that up to the fenderwell where I had room to drill a hole.

If anybody has ANY ideas that’d be great at this point. I can try and supply pictures if you guys are curious. I just ran thru most other vehicle 3G swaps and there’s a whole different setup of wiring that run off the main feed for each year and vehicle and maybe someone has encountered this before. Or maybe I’m the first person ever to put a 3G in this style of van? Who the heck knows. I’m gonna go check some voltages with my MM in between painting my roof!

This is my original regulator and wiring, I’m holding the 2 wire put that goes from the regulator to the alternator. Now I see a white/black wire that also goes from that plug and it actually terminates at the “fuel injection” plug where the voltage regulator r/g terminated along with a r/o wire and a y/g wire.


This is the weird plug I’m talking about. It appears the b/w wire originates from there and gets fed up to the alternator plug. Maybe this provides a 12V key on feeding FROM the plug?

Well I confirmed the r/g gets 11.8V with key on. I have a 3 amp spade fuse holder in that circuit as well and in the yellow wire that goes to the hot battery side. Would the fuses interfere with anything? The choke on my external regulator appears to be the blue wire which didn’t attach to anything since it’s EFI. Would I even be re-using that white/black wire then? It ONLY runs from the plug pictured which contains most of the external regulator wires to the OLD alternator plug. I’m totally removing my external regulator from the van. I could definitely run a line and splice it to the little alt plug. Would that mean that little plug would have 2 wires feeding to it? The white/black line from my fender, and also the white/black line from the new 3G D plug? On the belt issue this is a 6S serpentine with the automatic tensioner. I bet my van is where they switched to EFI and serpentine all at once which is why parts are always a “bring in and match” as opposed to “get what the computer says”

So the white/black wire they’re stating doesn’t correlate with mine. On the regulator my field is orange, attached to the alternator plug, which comes out with all the 1G wiring. The “S” is the green/red with hot in RUN, there is no “I”, and the “A“ is blue and is also removed with the old wiring. The white/black wire I have runs from where it says “same connector” on this diagram, straight to the old 1G alternator plug. So removing the old wires, this wire is the only one that gets left behind

Posting updates as I go:

I spliced the white/black wire that runs from that connector cluster over and into the white/black wire on the field alternator plug, plugged it in. Still not charging. I even checked on the alternator stud itself and only get battery voltage of 12.1. Does grounding the rear of the alternator case cause any issues? I’m going to move that 4G ground wire I have from the fender to an engine ground point and maybe that’ll alleviate any resistance. Funny thing is the belt squeal is almost gone now. I checked for any excess heat on the belt or the alternator pulley and there was no friction due to improper belt size.

I had the alrernator shop that clocked it remove the original charge stud so they could swap that “L-shaped” charge stud extender on that you see on the Taurus and Van 3G alternators. Could they have damaged the charge stud when they did this for me? He tested it and said it was putting out 14V anyway...

With the wiring undoubtedly correct (minus that questionable black/white wire) I’m going to guess that the alternator pulley is too big or that the alternator itself is bad. If the pulley was too big I would still see a charge though, right?

If moving the ground wire from the fender to the engine doesn’t fix anything I guess I’ll have to take it out and get it bench tested again

Key on I get 11.8V at g/r, I’m going to remove the fuse and see what happens. As far as the clocking aspect goes, an actual alternator/battery shop looked at it before saying they could do it. Once the guy saw it in person he said he did it all the time. From reading online it appears you disassemble the rear case and then you move the inner case where you need it and then have the rear case follow where you moved the inner case and then you bolt it back up. It’s a little more technical than that, but I mean the shop did it in about 40 mins maybe. I don’t know if he tested it before, or after he clocked it. It would only make sense to test it afterwards, right? I’ve seen that it can be done anyway and the alternator operates as normal.

The white wire I’ve been confused about is the original “STA” wire from the 2 wire plug from the original 1G alternator. This would normally be an electric choke on carb’d engines but where is this wire going and what is it doing on my factory EFI engine? Can I remove it? It does feed into that connector I pictured above though so if the “STA” terminal of the original 1G alt was sending it current what’s at the end of that white/black wire? Is it possible it dead-ends at that pictured plug?

so that “choke” wire the factory had on the “STATOR” side of my 1G alternator can be completely tied off? The way the alternator works it seems the STATOR sends out AC voltage only when operating...it’s just very peculiar what that wire would’ve been doing or sensing as it dead ends into that fenderwell plug. I CONFIRMED I get 11.8 Volts at key ON on the green/red signal wire. So if the signal wire is putting out correct voltage, and my yellow wire is looped back to get battery voltage, and the field plug goes back to the alternator itself, how would it not be charging? I’m going to take it out today and bring it to get bench tested I think. I’m worried the alternator shop screwed me over :/

Hopefully it’s under warranty regardless! Glad it didn’t cause a fire or anything though.

Anyway oreilley’s tested it, I observed, it passed everything..

Should I not be re-using the existing green/red “I” wire? It gets the 11.8-12V on key-on but I think that’s what’s wired into the factory ammeter. Do I need to run a separate key-on from the fuse box?

unrelated but maybe related, the headlight dimmer decided to **** on me and now I can’t get my dash lights to work. “Brake” and “CEL” come on so I’m gonna replace the switch first because those lights used to go out over the correct bump until I would roll the switch back and forth. Headlights work still.

Pretty frustrated about not getting this alternator to work though.