TBI 350 Swap Wiring Question

[Asbjorn]

I feel dumb for asking but....

Chevy TBI 350 into 1988 YJ (previously 4.2L) swap question:

I’m finishing up the engine wiring and have one straggler - two wires coming out of the Chevy alternator pigtail, I understand the red goes back to the battery, and the white goes to the volt gauge/dummy light. I can’t locate a spot on the YJ bulkhead to run the white wire to.

My research leads me to think that the white alternator wire could go back to the switched ignition start/run that also powers the + side of the coil? Will this work, or is there a better place to run it to?

Tagging a couple of folks I know running, or previously running this engine in a similar rig. I’m sure there are plenty of other.
@mbryson @Pile of parts @Bart

 

[boogie_4wheel]

I'm looking at my 88-98 Chiltons. I've loaned out my Haynes book or I'd compare schematics.
Red, brown, and if a 3rd wire 'rust'.

Red = battery
Brown = alternator indicator. This wire will go to the dash dummy light. The other side of the dummy light is connected to a keyed source.
Rust = ties right back with the red wire.

The pictures don't show the bottom (the alternator) on my phone unless I zoom then pan down. FYI... hopefully they display correctly on a PC

 

[Asbjorn]

Thanks for the diagrams!

Just to clarify, I’m running an older alternator with a pigtail like this:


I know what to do with the red, I just can’t figure out where the white wire needs to tie into the YJ bulkhead/harness.

All of the other TBI wiring is self contained in a standalone Performance Fuel Injection harness.

 

[mbryson]

I wish I was helpful. I’m running all GM wiring in my turd.

I don’t have a white wire? Is that from the Jeep harness?

 

[Asbjorn]

No, the red and white pigtail is from the Chevy alternator. For further clarification, this is a 1979-ish 4 bolt main 350 that has 80’s Chevy TBI components on it. Hence the older style alternator.

The only remaining YJ wiring in the engine bay is what comes out of the bulkhead by the brake booster. None of those appear to be the wire for the volt gauge on the YJ.

Just trying to figure out where the YJ volt gauge pulls its reading and that’s where I think this white wire should be. Wiring is not my strong suit. Kind of surprised this is my only question at this point!

 

[Pile of parts]

Just got home from hunting. Let me dig into my notes tomorrow and see if I can come up with anything helpful.

 

[Asbjorn]

Connecting some dots - with the info from @boogie_4wheel and the picture from @mbryson, I think my white wire serves the same purpose as mbryson’s brown wire (I think the one on the left side of his picture coming out of the plastic connector on the alternator is brown?). Any chance you can easily trace where that wire runs to on your YJ, please?

 

[mbryson]

So this wire you want me to trace? Likely be late tomorrow

 

[Asbjorn]

Yes, please.

View attachment 122819

So this wire you want me to trace? Likely be late tomorrow

 

[lhracing]

The white wire goes to the ING side of the ignition switch but it needs a diode in series with it to prevent engine run-on.

 

[Asbjorn]

I was just coming back to update with what I’ve learned, essentially what you just said. It needs to go to a switched power source. I can either 1) run it through an ungrounded idiot light for resistance, or 2) wire an inline diode between the alternator and power source.

Since my YJ has a volt gauge and NO idiot light, I will probably go the diode route. Still wondering if the + side of the coil is a good place to get the switched power in start/run?

The white wire goes to the ING side of the ignition switch but it needs a diode in series with it to prevent engine run-on.

View attachment 122829

 

[4x4_Welder]

You don't need either of those wires connected, however in order to initiate charging you may need to rev the engine.

 

[lhracing]

I was just coming back to update with what I’ve learned, essentially what you just said. It needs to go to a switched power source. I can either 1) run it through an ungrounded idiot light for resistance, or 2) wire an inline diode between the alternator and power source.

Since my YJ has a volt gauge and NO idiot light, I will probably go the diode route. Still wondering if the + side of the coil is a good place to get the switched power in start/run?

The + side of the coil should be fine as a source of switched power. Connect the RED wire to the large output terminal.

The RED wire supplies battery voltage to the alternator's built in regulator as a reference for the alternator's output voltage.
The WHITE wire excites the built in voltage regulator turnng it on.

 

[Pile of parts]

I looked at mine this afternoon. Unlike @mbryson , I have two wires like yours. However, mine are black and red. My engine compartment wiring is factory GM running to the GM bulkhead on the firewall. From there it goes to a painless style fusebox/wiring. I did not trace the two wires from the alternator since they were in wire loom/factory harness. My understanding is what you discovered, and what's been stated on here, as the white should be the exciter wire. Since wiring is not my thing, I have to assume my wires go to the proper place through the wiring harness. Everything seems to run fine. In my case it was better to be lucky than good.? If you still have issues, I can certainly try to trace back through the harness.

 

[Asbjorn]

Thanks everyone - I think I know where to go from here. Of all things involved in this swap, the alternator had me stumped! Now to get the fuel system plumbed and see if this thing runs!

 

[Asbjorn]

Sigh…here we are again.
I have a different alternator plug on this swap.


Red is obvious.
I believe the brown is the wire that should go to 12v switched power source? Diode needed?
Black??

 

[Asbjorn]

I think I found my answer. In my case, the black wire is unused. The brown goes to switched 12v. I’ll just leave this here for future reference.

 

[Mouse]

What alternator is this - CS144? or maybe 10SI?

 

[Asbjorn]

What alternator is this - CS144? or maybe 10SI?

Fairly certain this is a CS130

 

[NYCEGUY01]

Ive done those older alternators this way a bunch of times.
I run one wire from the fusebox (switched power) to the Alt but from the ign switch would also work, just need something with 12v when the key is on.