|Simplified SJ diagrams based on the 1983 and 1984 factory wiring diagrams and a real live 1985 Grand Wagoneer.
If you find errors, let me know. Tom Collins FSJ Wiring is a good source for looking at originals if you don't have your own copy.
Feel free to use, borrow, reprint with all the usual caveats including but not limited to; the risk is yours, not responsible for errors, and resale is prohibited.
1984-85 Starting, Ignition, and Charging System Wiring:
This diagram was originally posted on the IFSJA while figuring out why my FSJ 12SI alternator was different. I sketched out the alternator wiring because the 84-85 factory foldout breaks up the circuit, making it hard to follow.
Alternator terminal 2 senses voltage so the regulator knows whether to let more or less current into the rotor creating stronger or weaker magnetic field.
Alternator terminal 1 supplies power to the rotor (aka field) when the alternator starts up or isn't turning fast enough to supply the field internally. The 15 ohm resistor wire insures the internal field supply doesn't backfeed the ignition when the key is turn off.
As shown more clearly in the Lighting diagram below, power to subcircuits is distributed from a welded splice under the under the dash.
The ammeter only shows current flowing into or out of the battery from that splice. For an explanation of how that works go to Charging Systems with in-line Ammeters
1986 and later main power is quite a bit different. Power is distributed to the subcircuits in the engine bay see 1986 Starting, Charging & Ignition Diagram
Headlight and Fog Light Wiring:
1983, 1984, 1985 Factory fog light wiring were all similarly wired.
If you take advice, or copy something I have done, you are on your own. I'm just trying to be helpful, but you need to make your own decisions, and know about or discover the risks before barging ahead on any endevour.
The information and pictures on this page are free to use and share by all and may not be sold. If you use something for self profit that I have written, or a picture I have taken or drawn, you are a thief. Plain and simple. If you wish to quote something, you are free to do so. All I ask for is proper credit.
rev. 2. Jan 2022