It may have a relay for the thermostat but it doesn't sound like it has a relay for power in the sense that I'm talking about. Essentially, what you want to do is use another relay, use an ignition source to trigger the relay (easiest place to get it would be the wiring going to the fuse box), the main power will still be connected to the battery, the relay will basically see 12v ignition power, and switch on so that the fan is still drawing power directly from the battery, but only when the ignition is on. There may be a relay harness like this out there for sale somewhere already made. If I still had my truck I would go out there and find a good place for you to get ignition power, but I haven't had it in over a year and can't remember where it would be lol. If you need help wiring up a relay, let me know. I can tell you exactly what pins to connect to what. The only thing I can't tell you is where an ignition source is under the hood. It should be easy to find though. You can buy a relay for around a dollar and if you have some spare wiring around, it would be essentially free to do.