Starting/solenoid diagnosing

[Hinder_er]

Howdy,

Hoping I can get someone to decode this… 72 mustang my lady and I inherited is having some issues starting. The car is heavily modified, so I’m hoping I’m just missing something easy or a bad starter solenoid before having to trace all the wires. Here’s my readings from the starter solenoid.

The car will crank after bridging battery to S on solenoid
Voltage at the I position is 12v
Voltage at S position when key is turned to start is 6v

Is 6v too low at the S?

 

[midlife]

Yes, so long as you measured it with the wire disconnected. Even if it was connected, it should be battery voltage. You probably have a bad starter solenoid.

 

[will e]

Greetings.
To be clear, the engine will not crank with the key turned to start but will crank if you provide battery power to the S post on the solenoid.
You get a 6V reading from the wire that is connected to the S terminal when the key is turned to the start position. I assume this is without the engine cranking. I also assume with the key turned off this post/wire reads zero volts. What does it read when the key is in the 'run' position? (I am guessing 6 volts or none)

The "I" post has 12 volts when the key is in the start position.

My guess is your "s" and "i" wires are on the wrong terminals.

Remove the wire from the "s" terminal. Move the wire from the "I" terminal to the "S" terminal and see if the engine cranks with the key in the 'crank/start' position. Be careful because the engine might also start running even with nothing connected to the "I" terminal.