Vw t25 fan chicken switch wiring

I have been asked by a friend to fit a rad fan panic switch(chicken switch) , it's just a swith that switches the rad fan on, it's for an early t25 water-cooled with a torpedo fuse, fuse box I have found a diagram for a later one with blade fuses but the wiring is slightly different

The switch should work normally when off so rad temperature switch will switch fan on when chicken switch is off, if that makes sense,

I know a few of you have t25s aswell so worth asking , I've asked on club80/90 but had reply as far

Thanks

 

I think looking at the schematic the solution with or without a relay is to fit the 15 amp rated switch across the thermostatic cooling system fan switch sensor, or just go from the fuse via a suitably 15 amp rated switch to the positive end of the fan motor.

With the added thought that if you dislodge ancient wiring on a watercooled engine block you may stop it working. So splicing by soldering and wrapping with self-amalgamating tape or liquid tape would mean you havent dislodged the sensor wiring disabling it..with the consequence that the engine gets knackered as a result of loose wires caused by fiddling around , where if you just left it alone it would be OK.

Walk away unless very confident...

 

Thanks for your reply Mike, it's much appreciated,
I believe the wiring takes place at the fuse box end , so to clarify the fan would act as normal I.e cut in and out normally with the chicken switch in the off position,
When worrying you can switch the switch and the fan would come on early, I'm also going to suggest fitting a lower rated rad fan switch so it comes on earlier,

He's just a bit of a worrier and is new the t25

Cheers Mike

On a cheeky side, I don't suppose you could post a pic of the diagram and where to splice the switch in, it's worth virtual beer

 

Why do you need this switch? Why is a chicken involved?

 

Don't bother - check the thermo switch works, the temp gauge works and the fan operates. Drive it sensibly. Watch gauge.

I have taken a T25 all over the place heavily laden, and provided it is well maintained and everything works there is absolutely no need for a chicken switch - all you are doing is cooling it before it is strictly necessary.

As Mike says, you are just introducing a new failure point.

 

And it won't do any cooling if the engine's not running, as there's no water flow through the radiator...

 

He's just being over cautious , I don't have one on my 25 and I've done the nc500 and most of the UK in it,

He was concerned that when he was in traffic the gauge rose up past the led ,
I explained mine sits past the led but fan does what it's meant to do, and I've never overheated,

He has never had a classic before

I fitted a lower temperature switch in mine to bring the fan on earlier, which is quite a common "upgrade"

I'm just trying to do as someone has asked , if it helps him build his confidence up having the option it's a good thing

 

Give him a slap, tell him to pull himself together

 

Another option if you think it's getting too hot is pull over to the side of the road and brew up. Either that or trust that VW knew what they were doing when they designed and built it

 

T25 temp gauges do tend to vary where they sit at normal temperatures.. many sit just above the LED, some even below it… they didn’t have the flat spot between 80-100 like they do these days

If it doesn’t boil over, it’s fine.

Incidentally, the 2.1 injection models had a thicker Radiator, which gives better cooling, and can be fitted to 1.9s

 

The radiator is about 400 percent over sized , no need for a “chicken switch” better to learn the vehicle and the gauge readings etc , at what point the factory fan cuts in and out on the gauge etc , it’s much easier to see a problem before it occurs, adding a “chicken switch “ will mask problems and cause more harm than good in the long term

 

If you do need a switch for chickens, just wire it across/in parallel with the existing fan thermo switch.

 

That was sort of where I started..
Two alternate wiring arrangements, one at 110C with a relay and one at 95C without a relay.
In both cases, switch goes across the sensor


Dont forget there is also going to be an "analogue" wax thermostat in the coolant loop bypassing the radiator when the engine is too cold, so if it doesnt want the radiator in the loop it wont help turning on the fan to try and drop the temperature.. you are just wearing out the fan unnecessarily.


Its OK its a wasserboxer so it will be the corrosion from years of wrong coolant that will get it...

 

Would you mind just putting some x's where the chicken switch should be spliced into and which wires need cutting and connecting to the chicken switch
Thanks

 

I would just rummage round the back of the radiator, locate the two wires going to the thermo switch and splice a switch into those, so the switch shorts them together when it's closed.

 

I still think that you might not be the best person to do this job, from your confusion/comments..

I have marked the two obvious alternatives.

The third one is just to go from the fuse to the fan with new wires spliced in near the fan and near the fuse.