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EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hey guys wanted to ask I got a Guage 16 wire that goes to the starter and wanted to connect it to my mill spec connector but all my wires in the other side is all 20 Guage how many 20 guage wires should I use .I was thing of using 3 20 Guage wires should that be fine

Three 20ga wires/pins should be OK. That is 20A+ constant capacity, and the starter solenoid seldom runs for more than 10 or 15 seconds, and typically uses 10-20 amps.

Assuming you are talking about a common pre-engage type starter solenoid I would always go overkill on wire size, if you cant then you need to be more careful with fuse selection and location (or PDM settings).

When they are working as designed they should only pull high current for a very short burst then switch to a much lower current, often around 10A. But what many dont realise is this is due to there being 2 independent coils inside the solenoid, there is a very high current "pull-in" coil (~40A), and a lower current "hold-in" coil (~10A). The other side of the pull-in coil is connected to the starter motor side of the main contacts, so what is meant to happen is as soon as the solenoid contacts engage these send 12V into the other side of the pull-in coil effectively turning it off, this just leaves the hold coil energised.

What can happen in real life though is if the main 12V supply is ever lost to the starter then the pull-in coil is never going to switch off, so you will have about 50A flowing through the starter switch circuit for as long as the button is pushed.

That may sound like a fairly unlikely scenario, but I have seen the smoking starter wire quite a few times, and mostly in motorsport. It can be just from worn contacts in the solenoid, or it can be more unusual scenarios like after some maintenance someone forgot to plug the starter cable radloc back in, or left the starter cable nut loose, or the master relay is off but the starter circuit stays live (common in drag cars)...

Not my pic below, just something from google to make my explanation clearer.

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