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Heater wiring

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What vehicle is the heater unit from? 

From my 110 wiring diagrams - - - - - 

Green/yellow = slow speed

Green /slate grey = ful speed

Blue/green should be

Purple/green =12v from fuse box


The only blue & green in a 90,110 is blue/light green from column switch to wiper motor


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It’s a ignition-switched 12v supply into the box and then there are two returns which are switched to earth by the heater control lever, the full speed one directly and the low speed one via the resistor inside the heater case.

I put a Defender heater in my Series III and I used two relays to do the switching to ground as the Series switch is set up to switch the live and not the earth. So I had a 12v supply to the heater through an auxiliary fuse box and then both high and low speed switched to ground by relays, those being controlled by the factory heater 12v feeds. 

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Hi can anyone give me a simple wiring diagram for my lever type heater blower switch, i,m only getting 3vs at the live terminals but 12v at the fuse, does it go battery,-fuse,- switch,- motor? its not working at all, was trying to replace lever with a 2 speed rotary knob switch. also what is fuse 7 for, cos there a link wire from blower fuse to it?

Cheers Mike

Edited by macclad
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Yep, just run a fused feed to that blue wire and connect the other two the the existing motor’s feeds.  Then remove the live feed from the fuse box to dash switch and connect that terminal to a good earth.  That’ll get it working, but you’ll just have to make sure you switch it off before leaving the vehicle.  You can use the old positive feed to the switch to control a relay that will allow the new earth from the switch to connect to a ground in the dash, and then it’ll be protected from draining the battery by the ignition switch, just like before.

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