No Spark help
A gray wire is often tach or some sort of signal. The terminal looks like the one used with oil pressure senders. In the other photo there was a pressure sender or switch with nothing connected and a mechanical sender Tee'd into it. So my guess is that its related.
I've seen electric chokes that had a oil pressure switch (no pressure, no power) but don't know if that's what you've got. If so - find that supply wire (hot in run) and make sure its not shorting or grounding.
Don't know how you're checking for spark. While a screw driver works, an in-line tester is what I prefer these days. Cheap, consistant, easy to see and safer too.