MFA and Revcounter problems.... yes, another one!

[heraldcoupe]

I know this is a common issue and I've been through plenty of posts here and elsewhere looking for the answer.

Firstly, I inherited this 1991 8V GTi when my dad died a couple of years ago. When it came to me, the revcounter didn't work, nor the MFA, or most of the warning lights. The charging light works, as does the high beam warning, though the latter is rather dim and barely visible in daylight.
At the time, my mum (who doesn't drive) mentioned that my dad had the revcounter disconnected as he found of confusing (!), however the more I read, the more I'm convinced this is a red herring.

Having investigated at the time and asked questions here, I'd come to live with the problem, except now I'd like to improve the car's state of tune, the lack of MFA is an issue.

The relevant grounds to the engine all appear to be intact and measure negligible resistance. I have pulled the suggested fuses without any change, similarly disconnecting the battery overnight hasn't worked. The clock assembly is a single plug Motometer type, I recently purchased a secondhand replacement cluster which I was assured was in good working order, however switching to that one gives exactly the same symptoms.

Is there any recognised method of bench testing the spare instrument cluster to confirm that it is in fact OK, or otherwise prove that it shares an identical fault with the original?

Cheers,
Bill.

[oakgreener]

If the new clocks are the VDO ones, there's a good chance they will work. I believe the only ones that failed were the Motometer type. Not sure there's a way to check them out before fitting, but i suspect not. If there is, I'm sure it will be very involved

[heraldcoupe]

The replacements are also Motometer. There seem to be a few variations in the failure modes I've seen reported by various users, I'd hoped that even if the 'new' set didn't work, any fault would be different enough to at least give me some confirmation of whether or not the fault was with the clocks. Sadly both sets behave in an identical fashion - no oil pressure light, dim main beam warning, no coolant level indicator, no MFA, no revcounter.

Cheers,
Bill.

[Santiago]

Unlike the other warning lights, the main beam 'on' light is not an LED, but a little filament bulb behind a blue plastic filter.  I'd guess that your filament bulb (and the one the other clocks) has deposited some of its filament on the inside of the glass, hence the dimness. Here's a thread containing a picture of one in this state http://vwgolfmk1.org.uk/forum/index.php?page=topicview&id=electrical-faq_2%2Fhelp-main-beam_2

The other faults (and maybe even the above one) sound like a failure of the PCB where the coolant level/oil pressure etc. circuitry is.  I bet there's a local 5V regulator on there somewhere, and maybe some electrolytic capacitors associated with it; any of which may have failed, and taken out all the 'clever bits'.

I'd be willing to have a look at a set for you, to try to find the exact failure, with a view to fixing, if you want? PM me.

[heraldcoupe]

When I get  chance next week, I intend to strip down the 'new' set of clocks to see if I can locate any issues. The only discrete regulator visible is the 10V package affixed to the flexi-circuit. This is a standard component I keep in stock for other applications, so even though the measured voltage was OK, I swapped it out in case it wasn't supplying sufficient current - no such luck.

Is there a published schematic diagram for the Motometer clocks?

As an aside, did VDO produce a cluster which is an exact match for this application, ie single plug, 140mph speedo, 7000rpm tacho? Since I've been looking the only ones I've found to match are Motometer types.

Cheers,
Bill.

[jimjames]

If they're not working at all then it sounds like it's a problem with the car. I seem to recall when I had problems with my rev counter that one of the tests was to disconnect the oil pressure sensor to check that the dash showed correctly.

In the end I bought a replacement set from Ebay and swapped out the speedo from the old one into the Ebay set then fitted to the car so it retained the right mileage. Once done the rev counter and MFA were working fine.

http://vw-golf-mk2-gti.blogspot.co.uk/2014/06/vw-golf-mk2-dash-removal.html

Not long afterwards the wires to the hall sensor plug broke so I do wonder if that was the problem and it was giving intermittent readings. This is the wires that had worn through

http://vw-golf-mk2-gti.blogspot.co.uk/2014/09/golf-mk2-turns-over-wont-start.html

[heraldcoupe]

Funnily enough, I had a faulty hall sensor on my old 1992 Passat, this manifested as an intermittent revcounter some time before it started to give running problems.
None of the sensors makes any difference to the display when disconnected. I've still to make any inroads to testing the instrument cluster, too many other cars all needing work at the same time...

Cheers,
Bill.