Wiring diagrams for a 4 terminal solenoid show the small terminals marked I for ignition and S for start. My new one isn't marked. Does it matter?

 

I'm not sure if it matters!

On mine the "S" is the one on the passenger side center when mounted on the firewall with the tall part of the solenoid pointing upward.

Like this as if you were looking at it mounted on the firewall:

 

It definitely matters. Things won't work right if they are hooked up backwards and it's possible to burn up your ignition switch or wiring harness also. The terminal on the left is always the "S" or "start" terminal. On an OE wiring harness, the wire going to that terminal is always red with a blue stripe. The "I" terminal is always on the right. It is connected internally to the right post for the starter cable and is supposed to deliver a full 12V to the ignition system for a hotter spark during cranking. Most stock Ford coils had a resistor wire or ballast resistor in line with the coil and operate at less than 12V when the engine is running. The "I" terminal is not always used. If you hook it up backwards, you will be applying 12V directly to the starter through your ignition switch when you turn it to "start". Ugly things can happen when a starter tries to draw 100 amps through a 16 guage wire and a dinky little contact in your ignition switch!

 

That's good to know Joe.

I never got into the solenoids internals, and they always seem to have been marked.

It's nice to know they are standardized and how they work.

Learn something new every day - Thanks!

 

Thank you for the help. I have no existing wires or original solenoid to go by. From what I have read, the original 54 only had one terminal and it was used with a push button start switch. I am using an updated ignition switch with a terminal for start instead of the push button. I have converted to 12 volts also.

 

Look very closely at the top of the plastic where the terminals come out of the solenoid. Just replaced mine on the 58 and I thought I was in the same boat, no markings, but upon closer look found them on top of the plastic right above the terminal. If they re not there I'd take it back and get one that was marked... they are only about 12 bucks, I'd pay that to not fry a coil or wiring.

 

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