1G to 3G alternator swap - Quick question

Darkwriter77 · Jun 20, 2009

Swapping out the crappy old 1G alternator in my '84 5.0 CFI and swapping in a 3G alt from an early 90's Mercury Sable 3.0L wagon. I kept the stock plug from the Sable and I've got the 4-gauge power and ground cables all done and set. Everything's bolted into place and everything else is all ready to go, I just need to know what to hook this stupid green wire off the 3-wire plug into for a 12-volt switch-on source.

I know I could always run a wire all the way into the interior to the fuse block to get a 12-volt source if I absolutely HAD to, but that'd be kinda ridiculous. Isn't there something on the old external regulator's wiring harness that I could splice this wire into? Everyone keeps insisting there's a green wire to hook into, but there's no such colored wire anywhere in my engine bay that was connected to the old alternator or external voltage regulator - they're all orange or red or yellow.

I also dunno what to do with the old charge cable that went to the 1G alternator, or the wire that went to the Field post on the back. Do I just tuck them neatly out of the way, or can I safely clip those suckers off and tape off the end? And do I need to leave the old regulator in there, or can I unplug that and yank that sucker outta the engine bay?

Really need to get this thing finished up before the end of the weekend because this is my DD and they kinda prefer that I actually show up to work on Monday morning.

v8only · Jun 20, 2009

the green wire goes to a key on 12v source.

pull it from where you want.

the heavy fused 4gauge wire goes on the post on the back of the ALT to the batt side of the starter relay.

the other thin wire you can tie in to the back of the alt post.

that's all you need to make it work. the old wiring on the car is just that..old wiring that's not used any longer. I "think" you can make your alt gauge work by feeding off of the line at the back of the alt..not sure on that

Darkwriter77 · Jun 20, 2009

v8only said:
the green wire goes to a key on 12v source.

pull it from where you want.

the heavy fused 4gauge wire goes on the post on the back of the ALT to the batt side of the starter relay.

the other thin wire you can tie in to the back of the alt post.

that's all you need to make it work. the old wiring on the car is just that..old wiring that's not used any longer. I "think" you can make your alt gauge work by feeding off of the line at the back of the alt..not sure on that

That's exactly the main question of the thread, though - WHERE should I pull the 12v source from? Everything else is already bolted into place and ready to go, I'm just down to this one stupid little green wire needing a 12-volt source. Again, I know I could run a wire all the way across the engine bay and into the interior, but I'd rather not if there's something over there on the passenger side that I could tie into for a 12-volt key-on source.

Isn't there SOMETHING over there on the passenger side fender area that gets a 12-volt key-on current that I could splice into?

white 89 GT · Jun 20, 2009

I was looking for the same source two weeks ago and finally ran one from inside.

Darkwriter77 · Jun 20, 2009

Crap.

I ran a wire from the green/red stripe wire all the way over to the interior fuse block. Everything buttoned up and connected, I started it up, and checked my voltmeter. Guess what? It's not charging at all - 12.2v at idle and 12.1v at 2,000 RPM - and the thing runs like poo. Took the alternator back off, and I'm gonna have it bench-tested to make sure it's not a bad alt. If it tests good, then I have no friggin' clue what to do next, other than to throw the old POS alternator back on there.

v8only · Jun 20, 2009

and you're running the thick 4 gauge fused wire off the back to the starter relay on the firewaLL?

Darkwriter77 · Jun 20, 2009

v8only said:
and you're running the thick 4 gauge fused wire off the back to the starter relay on the firewaLL?

Yup. Ran new 4-gauge cable from the back of the motor to the firewall, as well as from the front end of the block to the radiator support, and the 4-gauge cable from the alt to the battery-side post of the fender starter solenoid.

Found out the alternator had a bad rectifier. Got the new one bolted into place and all now, I'm just trying to decide upon a better spot to tap into a 12-volt source than the fuse block. I've heard the small wire on the starter solenoid as a suggestion, but doesn't that only get current when the starter, itself, is being engaged?

Another suggestion was to tap into the positive side of the ignition coil - yea or nay?

v8only · Jun 20, 2009

no, because that wire is typically run from a ballast resistor, which has reduced voltage.

I'd personally tap it off the power wire for the radio. Tap that, and run a wire straight out.

LiquidGT · Jun 20, 2009

Use your voltmeter to find a 12v spot; the low coolant sensor or EVAP solenoid is a good place on an areo... IDK whats under the hood of a CFI car to tell you.

Darkwriter77 · Jun 20, 2009

Well, I took a gamble and ran the green wire off the positive side of the coil. Lo and behold, I now have 14.4v at idle.

Many thanks for the suggestions, though. I thought I knew 3G swaps front and back, but this one has made me feel kinda like a dunce, all because of one little wire.

HISSIN50 · Jun 21, 2009

Did you run the new excite wire through a ~500 ohm resistor? I would if you did not.

If you want, turn the key on and check for the OEM excite wire. This would be the preferred method of hooking this up. OEM alt's are not self-exciting, so the wire should be there.

v8only · Jun 21, 2009

hissin...not sure what that is??

I hooked my taurus 3g up in my 66 to a straight 12v switched on, and the fat 4 gauge to the relay...that's it

do I need a resistor in the circuit?? none of the wiring diagrams on the net I found had one

LiquidGT · Jun 21, 2009

v8only said:
hissin...not sure what that is??

I hooked my taurus 3g up in my 66 to a straight 12v switched on, and the fat 4 gauge to the relay...that's it

do I need a resistor in the circuit?? none of the wiring diagrams on the net I found had one

The reisistor is in the lower righthand corner of the diagram over the bulb. In the car its on the back of the gauge cluster.
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

I thought the resistor had something to do with the battery light bulb.

Darkwriter77 · Jun 21, 2009

HISSIN50 said:
Did you run the new excite wire through a ~500 ohm resistor? I would if you did not.

If you want, turn the key on and check for the OEM excite wire. This would be the preferred method of hooking this up. OEM alt's are not self-exciting, so the wire should be there.

No, didn't use a resistor. Never been given any prior indication from others' posts that I'd ever need one for this. Am I going to burn up a perfectly good alternator without one in place?

Which one is the excite wire on the old alt? Are you talking about the Field wire? Or the Stator wire?

HISSIN50 · Jun 21, 2009

The excite wire is the wire you've been fighting with (without it, the alternator will not excite). It's labeled I at the regulator and is light green/red.

You will find that even when you buy aftermarket regulator harnesses to put a 3G into a hot-rod (which has no battery light or any stock wiring), it will have the resistor in the I circuit (thus it's needed). The regulator opens and closes a grounding pathway (which is what makes the battery light illuminate and extinguish).

Darkwriter77 · Jun 21, 2009

'Fraid not, at least not on my car. Again, this is a 1G alternator I upgraded from, not a 2G. The voltage regulator only has three tires going in/out of it: "S" (stator), "A" (???), and "F" (Field). Yellow, orange/red, and red. There is NO green/red wire going to/from the regulator that everyone keeps mentioning, which is found on the '86+ models. I can take pics if nobody believes me.

If there was an "I" (ignition?) wire coming off the regulator, I would've just matched the 3G's "I" wire to the "I" wire on the old regulator's harness and been done with it, hence the reason I've been so confused about this whole thing. If this green/red wire everyone keeps insisting is there really IS there, I've not seen it anywhere underhood. Apparently, my car was either a one-off deal (damned CFI motor! ), or someone hacked/spliced in a totally different voltage regulator and harness ... but I don't see any spliced/taped connections anywhere at all, it all appears to be the stock 25+ year old junk.

jrichker · Jun 21, 2009

Maybe this will help...

Recommended changes to the diagram info...
Use a 130-150 amp fuse and a 4 gauge power wire.

Put a 3 amp fuse in the "I" wire that goes to the ignition switch

Darkwriter77 · Jun 21, 2009

Already got it wired up with 4-gauge cable for the power and grounds, so I'm all good there.

I could never find a 150-amp mega-fuse, so I'm rockin' the same 175-amp fuse I have on teh Notch and on Lynn's Capri. Better than nothing, I suppose.

As far as the ignition switch wire ... isn't that the same wire as the one I already spliced into that goes into the coil? I know it's a 12-volt wire that switches on with the ignition to let the coil know it's okay to do its thing. I'll add a 3-amp fuse to it, though, just to be on the safe side.

HISSIN50 · Jun 21, 2009

Darkwriter77 said:
Already got it wired up with 4-gauge cable for the power and grounds, so I'm all good there.

I could never find a 150-amp mega-fuse, so I'm rockin' the same 175-amp fuse I have on teh Notch and on Lynn's Capri. Better than nothing, I suppose.

As far as the ignition switch wire ... isn't that the same wire as the one I already spliced into that goes into the coil? I know it's a 12-volt wire that switches on with the ignition to let the coil know it's okay to do its thing. I'll add a 3-amp fuse to it, though, just to be on the safe side.

Sounds like a winner. Jrichker's idea to fuse it is excellent. If you made a new A (sense) circuit, protect that circuit as well.

For all I know you are not missing your I circuit. It's been forever since I looked at a stang of that vintage. If so, my bad Dave. I would still use a bulb and/or resistor (if both, in parallel), along with Joe's fuse, on that circuit.

1G to 3G alternator swap - Quick question

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