Do fit a fuse close to where you pickup the high power feed from the alternator output wire.
Does the TR use other relays? Most common car ones are 5 pin single pole double through (changeover) which can be wired as a simple on off too. If you already have that type on the car makes sense to use the same for your fan too as it can be wired as a simple on/off.
This shows a SPDT relay wired as a simple on/off.
