Help with heater wiring

I wanted to try and boost my heating a little before the cold sets in and liked an idea I saw about wiring a bilge blower fan in line.

Got the fan in place, but struggling to sus the wiring it in in series with the main fan

I have a very early defender
I found a wiring diagram on the net with a green/purple and green/yellow wires shown.
Thought green/purp or green/yell would be a switched heater live.
My heater box has purple and green wires coming in and out of it all over the place and one green and yellow, non of them seem to go live only with the factory fan on?
Purple/green and green/purple are live soon as ignition is on (and still live with fan switch on full) and green/yellow is never live (even with fan on)......I just realised I only seem to have full speed on my heater working though.....guess there should be slow speed half way on the lever also?
Struggling to make sense of it?

Any advice from someone more competent with the sparks would be greatly appreciated

Can't help much but I 'think' that the fan speed control is a variable resister, ie- the earth is varied to give different speeds, the positive remains constant?

I tried the bilge blower, tbh it made no difference,
Instead I bought a new std fan assy and when I took the old one out the rear bush had seized solid and the bush was spinning in the fan casing itself, its a pretty poor design.
The new fan made more difference on its own than the old fan plus the bilge blower.

Defender heaters aren't bad when they work properly. Before doing anything else, take it apart, clean out the leaves/dirt/dead rats etc and put it back together. Then check the rest if the system for air leaks, and flush the coolabt pipes out with clean water. You'll be surpsrised at the amount of crap that comes out!

Its mostly to do with heater output rather than air flow. If the heater can only put out a set amount of heat (because bit is clogged etc) and your increase the air flow all you will get is more air (at a lower temperature) rather than hotter air

I have fitted a bilge blower to an 1985 90, and found it helped a lot. IIRC there are three wires to the existing fan, earth, 1/2 speed and full speed. The heater switch makes it look like there is a variable resistor, but there isn't. You can vary how much air passes through the little rad in the heater box, and the same lever has 1/2 and full settings for the fan. I first blocked up the bypass in the heater box with sleeping mat and sealed all the gaps then disconnected the wire that operates the flap as it doesn't do anything anymore. This will make quite a difference to start with. You do lose the option to blow cold air - not really a problem where I live. The bilge blower has two wires - earth and +12v. I connected the +12v to the wire for full power at the heater box and the earth to an earth. So my settings are no fan, gentle fan (heater fan only) and max fan (heater fan assisted by bilge blower). Much better than standard. A 3inch bilge blower fits inside the wing heater intake box.

Here's my how to:
https://www.landyzone.co.uk/land-ro...pgrade-the-heater-blower.294181/#post-3652713