I have a starter solenoid go bad on a Ford F700, 1989 model.So I got another one for it.
I decided to check the coil resistance, to compare it with the old one. Both were around 4 Ohm. But it turned out, in the new solenoid, the internal coil was connected completely differently from the old one.
Both solenoids are nearly identical on the outside, except one is white, and another is black. Both are 4-terminal solenoids, with the “S” and “I” terminals clearly marked.
The old solenoid had the internal coil connected to the “S” terminal and the ground bracket, which I assumed was how all Ford solenoids would be wired.
However, in the new one, the internal coil is connected between the “S” and the “I” terminals.
Are there two types of solenoids?
I think this link sheds some light on this.
http://www.mytractorforum.com/622963-post8.html
However, the solenoid manufacturer should not use the “S” and “I” markings on the terminals with this alternate wiring, as this is clearly wrong and misleading.
On the starter solenoids I’ve installed on my prior Ford cars and my 70’s Ford truck the coil is wired between the “s” and the part that bolts to the body, chassis ground in other words. If the solenoid doesn’t make good electrical contact with the chassis, it won’t work. Maybe there are instances where that’s a problem and the “I” terminal isn’t used, so they make it the other way so the electrical contract with the body isn’t important for it to function. There was a thread here on this topic a few weeks ago, you might want to check there too.