Originally Posted by trib
On the starter solenoid, there are two switch terminals, one labeled "S" and the other labeled "I". This is the part from Van's. I'm assuming the "S" is for the starter switch. What is the purpose of the "I" terminal? Something to do with an ignition?
Yep "S" (for starter) gets momentary switched 12 volt power. A good approx wire size is about 18 awg and is fused with a 7 amp CB or fuse.
"I" is ignition and has to do with cars and coil point ignitions (** if you want to know why).
"I" terminal is powered with 12 volts when the normally open contactor closes. When you release the starter button the contactor opens and power is removed from the starter and the "I" terminal.
You could connect "I" to a panel start light if you wanted to, but 99.99% ignore it. I'd cut it off the threaded stud and save 2 grams.
(*** Don't get confused, this is NOT a run-on starter light.)
Make it look like this:
** What is "I" really for? Typical point-coil ignitions have a big resistor to lower the voltage to the coil, prolong point life. However during start, full avaiable electrical power goes through the "I" terminal to the coil. This assists starting, bypassing the resistor. Since voltage is down already due to the draw of the starter during cranking, the resistor is not desirable during start. Pretty common stuff in 1960's and 70's cars. Often this wire gets disconnected or broken and cars whould be hard to start. Common fix or check is check coil voltage during cranking. Often the engine would "catch" just as you let go of the starter. I had some old Chevy's.
*** Starter Run ON: Having a firewall contactor (solenoid) eliminates this worry or at least minimize it in theory. The worry is if the starter remains engaged to the flywheel the starter acts as a generator, causing electrical havoc. If you want a run on light, put it on the starter, not the firewall contactor. Not many put a run on light in their RV. Skytec has a run on light KIT
. It's just 20 bucks in wire, fuse holder, fuse, a few wire terminals, lamp and lamp holder. The firewall contactor should provide protection from run-on, but skytec claims that poor quality firewall contactors (made by White Rogers) or improper type contactors (continuous duty used, should be intermittent duty) where used on Pipers and Cessna's, which caused run-on problems. Here is their explanation
. It's not an issue with the contactor Van's sells (Intermittent duty made by colehersee). It's the right one. Run-on caused by our firewall contactor is a nil concern in my opinion. I don't see how our firewall contactor could fail or weld closed. Remove power from the coil, it opens. Most of the STUCK starter run-on stuff involve the solenoid ON the starter, so put the run-on light there, if you desire. Personally I did not bother. (Diagram