Scavenger fan overide without resistors.

[nth]

Ive been toying with fitting a scavenger fan manual override for a while now but didnt want to mess around with resistors, have the glow plug warning light flashing or interfear with the normal automatic operation of the fan. Finally got round to it the other day so thought i would share the details incase anyone else wants to do it. The only parts needed were a two way switch & some wire (2 core makes it easier). The whole job is done from the inside.
Using the wiring diagrams & the workshop manual i found that for the fan to operate the ECU earths the relay to close it & put the fan on.
Bear in mind this info applies to a diesel auto model, other configurations will be similar but will likley have different ECU terminal numbers.
Probably best to disconnect the batterie(s) first.
Remove the glovebox then the plastic cover over the ECU (2 x 10mm nuts). Unplug the 3 connectors on the ECU, its the biggest one we are interested in and its position 3T (should be a grey & black wire).
Strip back the black tape off the wiring a few inches to give you more to play wth.
Cut the wire a couple of inches away from the plug & solder your 2 core wire onto the cut wire from the ECU (one core to each end of the wire you have cut). Insulate your joins ideally with heatshrink.
Cut the 2 core cable long enough to reach where you want to fit the switch, i put mine on the lower dash by my left knee.
The 2 way switch should have 3 terminals, connect the common terminal to the wire that is now on the harness side of the ECU wiring. When the switch is off the common & one of the other terminals should be connected (confirm with a multimeter) connect theECU plug side to this terminal.
The last terminal on the switch should be connected to a good earth. now just tidy up & secure any wiring & plug everything back in.
This means when the switch is off the original circuit is still the same so the fan will work automatically as normal but when the switch is put to on the fan relay is earthed so the fan comes on, ive had it on lots over the last few days to test & im happy to report no flashing glow plug light when it is on.
I hope I have been able to explain that all ok. I have a (very crude) wiring diagam sketch that I will try to upload too, its sometimes easier to understand when you see it sketched out on paper.

[roosmith]

What made you take this route rather than the resistor method? It seems like an awful lot of faff to save having to use a couple of 10p resistors.

[nth]

I read on here about a few different methods, most were said to bring the glowplug light on when the fan is switched on.
The way I have done it is honestly not a faf, it taken me longer to research & plan it out in my head & look at the wiring diagrams/manual than it actually took to do the job. It was easily done & dusted in half an hour. It probably just sounds very long winded the way I have written it out above.

[roosmith]

Ah fair enough, was just curious as the resistor method is so easy and simple too.