Do you have AC on your truck? I have done several efan conversions and have found ways to simplify these installs.
If you want to go with a two speed setup, grab a volvo relay fan controller at any salvage yard. All they are is two relays built into one housing, with a high amp rating. This will simplify wiring and prevent that rats nest wiring look.
Additionally, consider a BMW dual temperature switch for two speed setups. They make adapter that lets you put a temperature sensor into your top radiator hose. There are other ways to control fans, such as temperature probes that you stick in the radiator fins or slip into the top radiator hose. I have tried these, but always end up tossing them. The radiator hose adapters tend to come in off sizes, but the BMW dual temp switch is beefy. This means you can easily drill out the current threaded hole in the adapter and tap it for the BMW switch.
To trigger the fan(s) to come on with your AC, you do not need to add an additional relay. Most people running a dual fan setup use three relays: one for high, one for low and then one for AC. This is unnecessary and just adds to that rats nest look. Decide if you want the AC to trigger high or low speed and then tie the AC clutch trigger wire to the relay, for whichever speed you have chosen. The trick here is to use a diode between the AC clutch wire and the relay. This will prevent voltage from back feeding to the AC clutch and lets you use multiple triggers on a single relay.
A single fan, single speed setup can be run with a single relay, which you can easily snag out of a salvage yard. Run your temperature switch or fan controller to the relays trigger pin. Then you can add in the AC clutch trigger, with diode.
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