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4.0 v6 Simple Starter Wiring Going Insane


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Dec 1, 2018
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Austin, Texas
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Hey fellow rangers, through a slew of craziness after my starter motor died some 6 weeks ago, I've somehow found myself in a extremely newbie mechanic situation. There is only one line ran from my fender mount relay down to my starter solenoid, which is attatched to my starter motor. One wire from my relay. Can anyone explain to me why I have two wires running down from what I can tell as my relay? And I don't mean two counting the thin little ignition wire, I mean I have two thick gauge wires that come down to my starter inside the same line, one red and one back, both with the same size wire and clipped onto the same little mounting bracket under my steering column, that run together as a pair from start to finish. Somehow I managed to get myself all turned around and believing one was a hot and one was a ground, and have not been able to get my truck to start despite replacing the starter motor, starter relay, battery, and using a voltmeter to verify I have 12.5 volts running from battery to relay, verifying my voltage drop was within .5 when turning the key to start, tested the starter motor with jumper cables and a jumper wire when it's no bolted to my truck and it works everytime flawlessly. But when I bolt it to my truck I can not through turning the ignition, using a jumper wire to bypass the ignition, jumping at the relay, no matter if I have either one wire connected to the post, or both.

Please someone help a guy out, everyone I know who has offered insight says thay cant imagine how I'm possibly finding myself in this situation. Thanks in advance, long time forum lerker-first time register and thread maker, James


Official TRS AI
TRS Technical Advisor
Jun 2, 2012
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Welcome to TRS :)

1994 was a transition year for starter systems
First some terms
Activating Relay causes an electrical connection
Activating Solenoid causes MOVEMENT

Some Starter motors have a solenoid on it to MOVE the starter motor's gear OUT to engage ring gear to turn the engine

This solenoid is activated by the stater motor getting 12volts

For many years Ford used a Starter Relay on the inner fender, often called a "starter solenoid", its not a solenoid, but thats another story, lol.

When you turned the key to START this relay was sent 12v on a smaller red/blue stripe wire and that would Close this Relay, sending 12v to the starter motor and its solenoid.

This relay was also used as the power distribution point for the vehicle, the Battery Positive cable was hooked to one of the larger posts on this relay, and several other wires were also hooked to this same post, like alternator, fuse boxes, and a few other systems that needed full time 12v power.
The other larger post on this relay just had ONE wire, to the starter motor

This relay would have 1 or 2 smaller posts, "I" post was dropped with electronic ignitions, it was for Coil Power
"S" post is for activating this relay, the Red/blue wire connected here

So pretty straight forward wiring
Battery + on one larger post(with several other wires)
Starter motor on the other larger post(ONLY wire here)
Red/blue wire on the "S" post, smaller post

And that was it

Now the transition..................
Newer model starter motors will have the "S" post so can be activated by the red/blue wire directly
Starter motor can be hooked to Battery positive directly
No fender mounted relay needed

But power distribution was still needed and all the factory wiring use starter relay post for that so it needed to stay until new wiring harnesses were made

So what Ford did was to use the newer model starter motors with "S" post and just added a new wire and moved another wire.

So what they did was to hook the starter motor(with "S" post) directly to battery, the RED wire, it can come directly from battery or can be hooked up WITH the Battery Cable on the larger starter relay post, NOT on the opposite post.
The black cable is on that opposite post, on its own, this is the new wire added

Black wire connects to starter motors "S" post, smaller post
So when key is in START the fender mounted relay closes, and sends 12v down the Black wire to activate the "S" terminal CLOSING the starter motors relay and connecting it to Battery voltage via RED wire

Red wire, is from Battery, full time 12volts, hooks to larger post on starter motor's solenoid/relay(there are two larger posts, hook to the one with NOTHING else on it)
Black wire from starter relay to "S" terminal on starter motor's solenoid/relay, smaller post

In later years the red/blue wire was just extended to reach the "S" post on the starter motor(and you can do that)
And Fender relay was replaced by a Stud, then Integrated fuse box
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