pm sent.

Alan if posting here no need to pm me.

Blue wire is I'm sure, glow plug. There is no blue wire from the FBH to my car.

macafee2

a bit of an update. I had a quick look at Alan's car and feel I did let him down somewhat as I was not in the position to delve deeply.

Pin 3 is being earthed. The wire starts as Blue and then is connected to a green wire that runs into the cabin to a push on push off switch and here it becomes complicated.

The switch has 4 wires I suspect :-
Earth from chassis to switch
Earth From switch to FBH
A live from somewhere. I presume this is used to light a light in the switch when it is on.
And the 4th wire, no idea what this does or if + or -

There is also wiring for I think a dash cam or sat nav and this does seem to complicate
things.

For some reason the fbh is starting when the switch is off. At the same time the light in the switch is coming on fully or in part.

There are wires that go no where.

Alas I could not test which of the wires did what on the switch, what the 4th wire does
or for any power being supplied inappropriately.

Alan my go to a nano meet. I think the wiring in the cabin can be improved but I feel it will need the assistance of a test meter
I think in one of the other posts it mentions a blue wire, this is the wire for pin 3 and not the glow plug.

macafee2

Thanks for the report, when you say it starts with the switch off, do you mean when engine started or as a parking heater, eg how does it get switched on ?

Do not fully understand, are you are saying when the FBH fuse is inserted the FBH fires up and runs, without being started by the temperature sensor or a remote switch, or does the air fan run continuously. If the air fan runs continuously and does not stop intil fuse is pulled, then there is a air fan short circuit on the PCB, This will not be a resistor fault, because I have yet to test a resistor that fails closed, they all fail open circuit.

If the FBH actually fires up and runs, diagnosis is simple without a meter. Remove the wire from pin 3 at the switch, if ok fit another switch. If the same, remove pin 3 of the 6 pin connector, if ok, replace the wire to the switch. If when pin 3 is removed the FBH starts and runs, remove pin 1, if ok, it is the sensor, although unlikely.

Hi Ian.
Thank you for your PM about the above when you tried to help Alan, now that Steve (Devlish ) & Rob (trebor) are on the case you will be in good hands I am sure though if you could make the September meet you would be going home with a fully working FBH after the two crew members have tested and scanned it for faults, Alan hopefully you can make it cheers Arctic

Thank you to everyone for your help - I'll get to the September meet somehow!
The electrician connected the blue wire in the Webasto plug to earth to trigger the unit, which works as expected when switched on. Because the switch is illuminated, he ran a power supply to it, so the switch should light up when it is "on" even though it is switching an earth. Strangely, the switch now glows half on when in the off position, sometimes switching on the Webasto! The SartNav only got involved because the Webasto wires are taped to the extra cigarette lighter socket that powers it, and it's temperamental . . . .

I have made up full wiring looms for our FBH heaters,and heaters from other vehicles,I only use 3 of the pinson the 6 pin plug,No 1 to start heater,No 2 for Diagmostics,No 6 fuel puump,No 1 can be activated by 12v by way switch,or triggered from timer,these heaters will run up to 5 central heatingradiators/showers etc on boats,caravans etc, Tom.

yes fbh fires up by itself when fuse 8 is in because I think the push on push off switch may be supplying earth due to a wiring fault. This is not happening all the time. The fbh itself seems to be fine. The push on push off switch lights up when pushed on but now even with it off it is glowing
and this is when the fbh is forced to start
macafee2

woooo folks don't get hung up on this blue wire. The blue wire soon turns into a green wire and is used to earth via pin 3. It is not the glow plug blue wire

macafee2