The last few little Gremlins

So after a successful 3 1/2 hour journey back from the AGM (a lot quicker than the 9 hours it took us to get there), and the cars first millage in 23 years, we still have a few electrical problems to sort out.

Any hints would be appreciated!

1980 1.6 GTI, (GCE187W)

Coolant temp gauge does not work. There is a 2 wire sensor on the top of the water housing on the front left of the head (the housing that is on the front right on the 1.8).
On ignition the temp gauge goes up to max, and the light flashes, but once running it returns to min and there is no further movement.
There is another single wire sensor on a housing on the end of the head, however I think we replaced this housing with one that possibly came off a different engine, and there appears to be no wiring for it.

The brake lights are constantly on, the only way to turn them off is to disconnect the battery, when the brake pedal is pressed the sidelights come on (but as these are less bright than the brake lights it is not very obvious. - Thank You to the 30 or so people that pointed this out to us at the AGM btw! (we were the ones disconnecting the battery every time we stopped!)

One further puzzle, behind the alternator, there is an earth wire secured to the block, it seems to be designed to bolt to the back of the alternator housing, but despite looking under just about every bonnet at the AGM, I couldn't see one similar (I think we were the only ones there with a 1.6).

We have had a lot of electrical issues on this car, It has a series 1 fuse box which is awash with scotch locks from previous owners attempts to get it running/add awful sound systems we think. Hence the fuel pump is now on a switch and the hazards/indicators had to be rewired,

Thanks Guys!

the temp sensor is a single pin black collar unit, which is fitted into the flange on the side of the head,. wire colour is red/yellow. if you fitted another flange without sensor, that'll be why

brake lights sounds liek earth fault and/or you got your spades mixed up, the red./black wires are for the brake lights. check the pressure switches in the engine bay as well should be open circuit till you press the brake pedal.

the alternator earths direct to the engien block, but more earths cant hurt tbh

Thanks for that, really helpful as always. The car is back for a couple of days, so just had a look

with regard to the temp sensor, there is a single pin sensor (spade terminal) screwed into the end of the head, just above the water housing, this has a thin red/yellow wire going to it. There is also another single wire sensor (the type with a nipple style connector on the top) screwed into the actual water housing on the end of the head, however this has no wire going to it. Should the red/yellow wire go to the sensor in the housing? or the one that screws directly into the head (as it currently does). It still seems odd that there is a two wire sensor fitted into the water housing on the front of the head, which appears to be unique to the 1.6.

The Wiring on the rear light clusters all looks fine. The pressure switch on the offside of the master cylinder feels hot when the battery is connected, and if i remove that plug connector the brake lights go out. The switch on the other side does not feel hot, and it appears to make no difference if it is connected or not.

Thanks for your help!

yup, the one in the head itself is the oil pressure switch and should have a yellow wire. sometimes the ealry mk1s only have 1 pressure switch so this might be why you dont have a wire for this one.  move the red/yellow wire to the sensor in the flange

the 2 pin one on the front is the thermoswitch for the 5th injector, this should have a red/black and green/white wire to it

sounds like the 'hot' pressure switch is stuck on, and is being heated up by the voltage going thru it. unplug that one and only plug in the 'cold' one, see if the brake lights start working. my old cabrio had exactly the same issue, one of the switches stuck on so i had to unplug it and only use the other one

Thanks, that's really helpful, unplugged the pressure switch and brake lights work perfectly now. Swapped the yellow/red wire to the temp sender, and the gauge works too! Cheers! Will order a new brake switch, as I guess there is a reason it has two :p

its so if you loose one of the brake circuits your lights still work, you now have a 50/50 chance of the 'wrong' circuit going and your brake lights stop working too. but tbh if i lost a brake circuit the last thing id worry about is my brake lights

an alternative option is mount a later mk1/mk2 pedal switch, need to mod the pedal box hole slightly so it fits bit nothing difficult.

if you go for the pressure switch its just a case of you'll have to bleed the system after