‘72 Starter Solenoid Wiring Help

‘72 304 (original wiring set up)

I’m probably over thinking this but it is my first time doing under the hood wiring. I’ve read previous posts and am still unclear.

My ‘72 TSM (pic attached) shows the battery positive coming into the large post of what I’ll call the “S side” of the solenoid and the light blue ignition wire as the only thing attaching to the small “S” terminal. On the “I side” large post is the starter motor cable and connected to the small “I” terminal are BOTH the green by pass to coil and alternator regulator wires.

When I got it (attached) the Jeep was actually set up with some things reversed (ie. Starter motor wire was on “S side” and light blue ignition switch wire was on “S” terminal). I thought the PO may have made a mistake, but now I’m finding tons of diagrams, some posted on this forum, and even the Haynes manual that show it as the PO did it, opposite the TSM.

I have the direct replacement SS581T solenoid. Should the solo light blue ignition switch wire connect to the small terminal on the battery cable side of the solenoid or the starter motor cable side (and therefore the other two wires on the other small post) or does it even matter?

(Don’t worry, re-doing all those bad original wires!)

 

Here is a little better (less zoom) picture of how things were set up by the PO as well if that helps. It just seems like the way the small terminals are set up is backwards.

 

First, don't refer to the Haynes or CHiltons manuals. They are full of errors, and cover too many years.

The SS581T is Standard's (SMS) cheapest line of parts. "T" means cheap, cheap cheap. Suggest you return it and get the SS581, or another brand that is specifically sold as "premium."

Here is from the wiring diagram at the back of the TSM, which agrees with what I presume is a diagram from the middle of the book.



This is right. Be sure you are looking at the solenoid from the same end as the drawing.

The circuit will still sort-of work if you connect the big cables backwards. However, "I" will be hot all the time, and you will get full battery voltage to the coil all the time if you connect that wire. Suspect the engine would then not shut off. Use your meter, and determine which big post connects to "I." This must be the switched post (ie the one that goes to the starter).

Suggest you also understand how this circuit works, not just copy the diagram. Take apart your old solenoid, and measure the connections with your meter.

The solenoid's main job is to bridge between the two large posts and run the starter. There is a coil inside that throws an copper disk across the posts to accomplish this. One end of the coil goes to the "S" (start) terminal, and the other grounds to the fender through the bracket. You must have a good ground, from the brakcet to the fender to the body to the battery. When you turn the ignition switch to start, that coil is energized which connects the battery cable to the starter. The "I" terminal is also connected to the big post that goes to the starter. It goes to the ignition coil, bypassing the coil ballast resistor when the starter motor is running. This juices up the ignition during starting, for easier starts.

Suggest you look at the Jeep as your ultimate reference, not the books. If you understand how the circuit works, and you see where the wires go, there can only be one right way to connect the solenoid.

 

Another point - you can usually fix these solenoids to work for a while longer, as long as the coil works. Drill out the rivet in the center and take it apart. The disk is usually held by a clip and you can turn it over. File the posts to remove any burnt part. Put it back together with a long screw - walla.

This also works on the GM-type solenoids that mount on the starter, IME.

And clean/check the ground.