Honda powered trencher, electrical questions

[V65ozzie]

I'm re-engining(sp?) a walk behind trencher. The GX440 engine on it has been problematic at best, and finally it swallowed a piece of the choke butterfly. After much research and discussions with the manufacturer, it turns out that the machine is identical to their previous model except for the motor. So, tossing all the electronic etc in the garbage leaves me with a new GX390 motor. It's pretty much a bolt in, transferring all the switches to the motor instead of the machine body, which I'm fine with. I have to add a battery tray, the 440 was pull start only(who came up with that idea?) The 390 has electric start, and wiring in a battery is simple. But, the machine has an electric fan for the oil cooler. Obviously I can wire direct to the battery because it would run all the time. I do not want to wire in a switch, simply because someone will forget to turn it on. So, I want to run it through a relay, triggered off the start switch. And here is the problem. I cannot find a diagram that telsl me which wire I can tap to trigger the relay when the engine is running. Basically, power form the battery to the relay, from the relay to the fan. But where can I pull a signal from to trigger the relay? Possibly the red wire from the ignition coil? I'd appreciate any help you guys can offer. Thanks in advance

 

[Tazza]

Being electric start, there should be a key to start it, you should have switched power to it, or at least that is how ride on mowers are.
Should be switch to on, then start, you will need to check voltage on the pins on the switch.
I don't know if there will be enough power on the red wire to the ignition coil to power a relay.