Temperature and fuel gauge faulty

[mike35]

I got a VW 1.6 TD T25. My temperature gauge is reading 3/4 of the way up and my fuel gauge is saying empty when there is 1/4 of a tank, and when i put £10 worth of fuel in its saying half a tank which i know isnt right. The temperature gauge must be faulty because ive just had a brand new head, water pump, thermostat and radiator fitted. Its all been bled, heaters and rad are warm. Do anybody know what the problem could be?? (Thank you).

[ajsimmo]

Could be voltage stabiliser on back of dash (3 prong transistor), which from memory should output steady 10V to fuel and temp guages. Normally when they go your guages won't work at all, but could be bad connection there.

[California Dreamin]

As Andy says ^^^^^ they don't just fail but can also misread.
Cheap enough but as I've seen a maplins part number been banded about on here, I assume that they are an obsolete part from VW?

If my memory serves me right the replacement part is a straight swap apart from having to fit it upside down because the 2 outer prongs are reversed? something like that.

Think it's Oldiebutgoodie who knows the part number but a search on the Wiki may reveal it?

Martin

[Oldiebut goodie]

If you are reversing a normal lm7810 and mounting it in it's original position you will need to pack out the tab with metal so that the heat sinking works or add one (suitably supported ) the other side. You won't find a part no. for a heatsink - make one out of a piece of scrap aluminium. The tab is the earth.
This was my post in that thread.

It looks as though http://www.powercomponents.nl" onclick="window.open(this.href);return false; have them.
or quote from an Audi site
"LM78M10 or LM342-10 would work just fine (and you can cross-reference
these numbers to other manufacturers as well). The only caveat is that
the pin-outs are reversed on these parts (input, GND, output). So, when
mounting these on the cluster you need to do so with the part's face-side down to match the flex circuit's pin-connections."
E D I T:

Done some googling
available in the UK £65 each!!!!!!!
available in Ireland 39.90 euros each!!!!!!!
Taking the p*ss a bit for an 80p item.

Stick with reversing a LM7810,these are good for up to 1A using a metal spacer to transfer the heat, if you haven't picked one up elsewhere.

Edited by oldiebut goodie - 29 May 09 at 22:01

[ghost123uk]

And in our wiki up there ^^^^ = more info

Part available for peanuts HERE

[California Dreamin]

Just be aware that they get warm so need to have a 'heat sink' bolted/screwed to metal normally to draw away the heat.


Martin

[murrayslinn]

Hi,

Having traced my temp gauge problem back to the printed circut board im sooo close to finding the problem.

The copper terminals that connect the printed board to the plug arnt in bad condition, its just the 2nd and 5th one in that are linked with a small piece of copper folded back over the back of the plug. I have bridged the wires before the plug by cutting both and reconnecting with a bridging wire.

Good news is the gauge and LED now work.......but only when the headlights are on! when the ignition is on and the lights are off the temp gauge goes to the far right and the LED flashes constantly

I have checked all of the rest of the circit and it seems to be fine. No blowin fuses, Im guessing it has to do with this connection?

Any ideas? is this bridge a bad thing for any reason?

Thanks

[ghost123uk]

I cannot give you a "do this and it will work" solution, but it sounds like you are methodical enough (and have a multi meter - yes ?) to get to the bottom of it. Bad earth's are often the cause of symptoms like this, but not always!

I popped in to say that yes, bridging wires onto damaged ribbon cable connectors is quite OK (and often done on our vans and elsewhere) = Providing you take care to make sure that, A) = you are bridging summat that is actually SUPPOSED to be connected, and B) = that you take the care to make sure you are bridging the correct contact to the correct matching contact - if you get that wrong you run the risk of confusing the problem or worse = burning summat out ! (as I am sure you already know)

Let us know how you get on.

[murrayslinn]

Thanks for that. I think that its something to do with that setup as it seems to have interferred with the dash light bulbs too. Will try and trace it tomorrow and see what happens. Might try bypassing the plug completly or checking those terminals again with the metre to double check that both pins are actually connecting.

Guage and LED seem to be working fine although showing a little on the colder side of half way. just not ideal to have to have the lights on all the time to read the gauge !

thanks again