Temp gauge goes up when lights on

Post by **pgm500** » 02 Dec 2007, 23:14

HI Folks,
1986 1.9 watercooled.
All been fine for ages, then noticed one dark morning that the temp gauge was over just to the right of the central indicator light, rather than just touching the left hand side as normal. As dawn broke, switched the lights off and immediately the temperature dropped to normal. Further experiments showed that when this happens even switching the lights off and back on a couple of seconds later has the same effect.
From the depths of my general ignorance of all technical matters I'm thinking perhaps alternator belt? alternator itself? Any advice much appreciated.

Thanks,
Paul.

Post by **Westy.Club.Joker** » 02 Dec 2007, 23:41

Electrical wiring fault, possible an earth problem?

Post by **Mocki** » 02 Dec 2007, 23:53

poor connection, and or bad earth in engine bay, check the earth strap to the engine, and the earthing near to the ingnition unit on the nr side wheel arch......, are you getting simular effect when braking?

poss bad connection on instrument cluster multiplug, ( above your right knee when driving) where plastic pcb connects to loom

Post by **pgm500** » 08 Dec 2007, 17:44

Thanks for the advice Gents,

Perhaps even a numbskull like me should have thought that weirdy electrical things are often related to earthing problems.

So, broke and reconnected that instrument cluster above the right knee (it looked ok), and checked out the earthing 'crowns' behind the fuse box - some of those had corrosion so cleaned them up - and that seems to have done the trick.

Possibly another silly question, but was the temp gauge going up just an electrical blip, or was the poor earth actually causing an increase in temp?

Thanks again.

Paul.

Post by **edoh** » 09 Dec 2007, 00:00

how did you get at the instrument cluster multiplug (above the right knee)/? do you have to take off dash/ Steering column cover other parts? Wires from the multiplug run to?...Cleaned with?...
Its the next job on my list! just done the earth crowns and fuses and fuse holders.... any tips gratefully received -

Post by **tonytech** » 09 Dec 2007, 10:37

pgm500 wrote:
Possibly another silly question, but was the temp gauge going up just an electrical blip, or was the poor earth actually causing an increase in temp?

Thanks again.

Paul.

I very much doubt any change in actual engine temperature/

If you have a poor earth, switching any thing ON will cause a voltage drop across the bad earth.
This voltage drop will affect any other equipment earthed at the same point.
The temp circuit takes very little current ( so very little voltage drop) but the lights take a lot more.

Lighting current may be flowing to earth through the gauge if it cant find a path through a bad earth.

Sorry if this confuses, It is difficult to describe the way electrics behave.
T

Post by **pgm500** » 09 Dec 2007, 11:51

how did you get at the instrument cluster multiplug (above the right knee)/

The cluster I had a go at is visible if you get on your back down by the brake/clutch pedals and look up behind the dash. I didn't do anything with it other than separate it and plug it back together. I think that was the one Mocki was referring to but might be wrong. No idea what all the wires do

Paul

Website · Post by **CovKid** » 11 Dec 2007, 12:30

Those second hand lighthouse bulbs you bought from that bloke in the pub might be the cause