Water temp warning light

Does the water temp sensor that's screwed into the metal hose under the bonnet also control the warning light on dash?
Mine is flashing constantly but needle works perfectly, temp sensor is new.

The flashing light is low coolant level warning, there is a sensor screwed into the top of the expansion tank, either the coolant level is low or the sensor is faulty the metal probes can rust away or you have a electrical fault.
First link I found to what the sensor looks like.
http://www.ebay.co.uk/itm/Expansion-Tank-Water-Coolant-Level-Sensor-VW-Golf-Mk1-M2-Polo-T25-K-Jetronic-NEW-/360851759900?pt=UK_CarsParts_Vehicles_CarParts_SM&fits=Model%3AGolf&hash=item540470e31c
You can see it on this expansion tank.
http://www.ebay.co.uk/itm/VW-MK1-GOLF-CABRIO-GTI-RADIATOR-EXPANSION-HEADER-TANK-COOLANT-LEVEL-SENSOR-CAP-/310936719367?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item486545d007

its also overheat warning which is indeed triggered by the coolant temp sensor, the sensor can fail in such a way that light is triggered even though gauge shows normal as I found out.

try bridging pins on level sensor plug if flashing stops coolant is low, switch faulty or tips dirty. if not wiring, relay, temp sensor or dash fault. pull the 42/43 level warnign control relay out of its socket. if flashing stops its the relay or level sensor wires, if not its coolant temp sensor, clocks or wire fault

Ok cool.
When the rain stops I'll have a go! Lol
I have disconnected the temp sensor and level sensor, light still flashes.
I will try bridge the level sensor and try that.

Right I have tried bridging the 2 terminals on the level sensor.
Light still flashes!
Can incorrect water flow effect this light as the water hose I replace has a bit of a kink in it. New one on order.

Earthed temp sensor wire also, gauge works fine!
Just the light that's has an issue, bugging the hell out of me.
You say 42/43 relay, is that the name of it as by the look of the fuse/relay diagram, relays only go up to 24?

I had the same on mine not long after I'd bought it… Turned out to be a loose crimp on the yellow wire that pushes onto the sensor where the main coolant pipes connect onto the block. Sure you'll get it sorted with all the knowledge on here!

as in the one with 42 or 43 on the front

it should be clipped to the top of the fusebox, look for the holder with red/yellow or blue/yellow, plus red/blue black/yellow and brown wires to it.

bridging the pins on the level sensor plug will rule out any issues with flow/level/whatever and point back to the relay, wiring, temp sensor or clocks

I know, sounded like a dumb question lol
Got one with 43 on it, no 42

rubjonny said

as in the one with 42 or 43 on the front

it should be clipped to the top of the fusebox, look for the holder with red/yellow or blue/yellow, plus red/blue black/yellow and brown wires to it.

bridging the pins on the level sensor plug will rule out any issues with flow/level/whatever and point back to the relay, wiring, temp sensor or clocks

Note the words "42 OR 43" (meaning you will have one or the other)     

Yeah got it, sorry lads, not well today, preventing me from reading properly. Lol

Well pulled out relay 43 and light is still flashing, I am very puzzled now, surely it shouldn't work at all after that??

Would one say this relay is not doing anything, although even when pulled out my light still flashes lol

yeah that is definitely past its best! with the relay out disconnect the red/yellow wire from the sensor on the head and see if it still flashes. if it does its wiring or clocks at fault, maybe the wiring has been damaged same as the relay!

the coolant temp wire goes to bot the relay and the fusebox so it can be damaged if the relay suffers water ingress. what happens is the level sensor pin seals fail and coolant wikes its way up the level sensor wires into the relay and rots em out, I see it all the time on the looms I make

Great, thank you for your help on this Jon, massive help.
I will do my best now to get to the bottom of the problem.

Keep you up to date

Well took the temp sensor wire off, light still on.
Could there be a fault with the temp sensor itself, although it's only 2 months old. 

if it still does it with the wire off and relay removed its not the sensor, its a problem with the wiring or the clocks

Oh dam it lol
Well I think I will check the fuse box first as my oil light and buzzer is playing up too
Does anyone have a diagram of the back of the fuse box?? 
Asking a lot here I think

Don't worry Penny on the Big Bang Theory drives around with her warning light on all the time.

Does not seem to do her Golf any harm, it only upset Sheldon.

Well I have briefly inspected the fuse box and other than the terminals for relay 43 being a bit green, it all looks normal, starting to now think my clocks are to blame.

I had this problem with mine, disconnected sensors, removed relay and still it kept flashing.

I had another problem with all the clocks going dead when I switched the lights on, the earth on the rocker cover seemed fine, in desperation as MOT was due and I needed the main beam warning light to work, I started to take the instrument binnacle out, but could not release the speedo cable, pushed everything back and by fluke everything worked when the lights were switched on, and the temp flashing cured itself. So might be worth checking the wiring plug on the back of the instruments in case it's loose.