[patrickt]

There is an advantage to having your blue light wired directly into the fan feed wire and not into a current trigger device and that is troubleshooting. Since this new circuit is not controlling any mission critical or life-death condition (like turning your natural gas supply on in your oven even though the ignitor is broken) all it's really doing is alerting you to whether voltage is being sent directly to your fan. Now, with a nice quality SPAL fan, and a decent wiring installation, the odds are overwhelming that if the blue light is on your fan is on and, unless the little blue light burned out or blew its fuse, if the light is off then the fan is off. But what if the fan is off and the blue light is on and your engine is hot? Then that would tell you the fan has failed but the relay is working. It also tells you the thermostatic switch is working. A current measuring circuit wouldn't tell you this, it would just leave the bulb off and you'd have to manually test both the relay and thermostatic switch.