It was a bit fiddly and I'll have to remember exactly what I did. My design needs a little refinement as I ended up needing to add a heat sink which is not ideal. I'll hunt around for the schematic when I get a chance, the best bit was it's totally reversible and is a bolt on to the existing tack, there's a thread on what I did here http://datsun1200.com/modules/newbb/v ... id=291394#forumpost291394

I'd suggest a higher resistance and more winds, maybe double the winding count and double the resistor value. I calculated less than the 5W rating but it got hot and stopped working.