The best method for you might be to create a separate small floating/isolated rectified system.
Your AC (which has one side grounded as stock) is fed into a full wave rectifier (TrailTech regulator-rectifier or similar). The rectifier OUTPUT is NOT grounded and is treated just like DC battery voltage. This can be hooked up as explained in the previous post.
The only down side is that the fan may run slower at idle (just like the headlight is dimmer at idle). So the headlight AC supply (yellow wire off the stator) and chassis ground are connected to the rectifier input.
Alternatively you could use the white stator wire and chassis ground to the rectifier input. The voltage output on the white wire is bit higher. As previously mentioned you must know the workings of the relay to ensure it meets your needs.
In your case I think you could do away with the relay completely and just let the thermoswitch carry power to the fan. Note that I used the word thermostat in the previous post; the correct name is thermoswitch. Does the fan have a current rating listed on it? Does the thermoswitch also have a current rating? Maybe googling the part numbers will find some details.
Your AC (which has one side grounded as stock) is fed into a full wave rectifier (TrailTech regulator-rectifier or similar). The rectifier OUTPUT is NOT grounded and is treated just like DC battery voltage. This can be hooked up as explained in the previous post.
The only down side is that the fan may run slower at idle (just like the headlight is dimmer at idle). So the headlight AC supply (yellow wire off the stator) and chassis ground are connected to the rectifier input.
Alternatively you could use the white stator wire and chassis ground to the rectifier input. The voltage output on the white wire is bit higher. As previously mentioned you must know the workings of the relay to ensure it meets your needs.
In your case I think you could do away with the relay completely and just let the thermoswitch carry power to the fan. Note that I used the word thermostat in the previous post; the correct name is thermoswitch. Does the fan have a current rating listed on it? Does the thermoswitch also have a current rating? Maybe googling the part numbers will find some details.