This may sound like a daft question but i'm asking it anyway..

I have a 78 Crew Cab and have been slowly preparing it for a Roadworthy. Bit by bit i'm sorting the electrics but I'm a little unsure about the heater booster fan and how it should function?

Is it manual, should there be a switch on the dash or is it activted by the heater levers on the dash...or...should the fan be spinning as soon as the engine is fired up and continue to spin?

I'm sure you have gathered mine hasn't responded so it requires alittle work.

Can any of you guys provide me with the information to help me rectify this problem?

Cheers all

It works off one of the levers on the dash.

It'll only spin when your CC is running, not just on as it functions from the alternator.

I just got mine working. I'm working towards a roadworthy too. While you are at it, dismantle the fan and lube the bearing sleeves.
I didn't do this first and it nearly caught on fire! lots of heat and lots of smoke.

It pays to bench test the relay and the fan. Check it all works.

To elaborate on Tristan's response:

The fan is activated when the lever that controls the heat is most of the way down. This makes a connection to -ve back to the relay in the engine bay. The other side of this relay is connected to the wire that runs the alternator light on the dash. This means the fan will only run when the heat lever is down and the engine is running.

Much more eloquent than my explanation. Thankyou.