Hi, I have a 1990 Polo (1 litre engine). The fuel gauge and temperature gauge occasionally used to stop working whilst driving along. This was an intermittent problem and apparetly happened at random. When it happened, it would last an hour or two or maybe till the next time the car was started. However about a week ago it became permanent. So now the fuel gauge and temp gauge are permanently not working. This problem also affects the cluster of warning lights in the middle of the instrument panel, but does not affect the time clock or the speedometer. All other electrics (eg, external lights, internal lights, wipers, etc are working fine).

 

Anybody have any ideas what the problem might be? I am quite happy to dismantle the instrument panel, I just don't know what to look for after I do that. I'm hoping somebody can give me a few pointers to find the cause.

 

Thanks

That sounds like the voltage stabiliser unit in the speedo has died,  Try VW Heritage they probably will stock them

Thanks for the advice.  VW Heritage don't have them.  Actually I can't find them anywhere so far.  Will continue searching.  Thanks again.

Welcome to the Forum.

 

If it proves impossible to obtain a voltage stabiliser, you may be able to obtain a unit that could be wired in there, but would probably NOT fit into the same physical space - also you may have to pay more for it.

You could ring your local RS Components and ask if they can recommend anything. If you simply look in their catalogue, you would possibly end up seeing something like Stabilised Power Supply Units - something that you definitely DON'T want!

 

Regards

is this it

 

https://www.ebay.co.uk/itm/AUDI-VW-Mk1-Mk2-Golf-T3-T25-80-90-100-171919803-Dash-Voltage-Regulator-Fuel-Temp-/133068981542

Thanks for the comments you posted.  I have actually now fixed the issue. In case it's of any use to anybody else, this is briefly what I did:

 

First I searched around for a suitable voltage stabiliser.  That took a long time but I finally I figured out that I could use the same voltage stabiliser that was detailed on this page: www.cabby-info.com/gauges.htm.  From that page, I got the "Type" of the voltage stabiliser, and then I located a replacement of the correct type (KA7810AETU) on Ebay.  I ended up buying this one:

https://www.ebay.co.uk/itm/ON-Semiconductor-KA7810AETU-Voltage-Regulator-1A-10-V-3-Pin-TO-220/173386050782?epid=9021013911&hash=item285e9d2cde:g:JPEAAOSw5KFbNmV4

 

Then I removed the instrument cluster from the dashboard.  This was straightforward, but slow-going because obviously there wasn't much physical wiggle room.  Once I had removed the instrument cluster, I located the voltage stabiliser and removed it.  It's not soldered in, just push fit.  I removed it and tested it.  It actually tested fine.  But I assumed my test must have been flawed, or the voltage stabiliser was only working intermittently, and I went ahead and fitted the new one I had bought.  I also tested the new one before I fitted it, and it was also fine.  To fit the new one, I needed to bend its legs into the correct position, and break off one of the plastic locating tabs on the instrument cluster.  Eventually I was able to fit it and attach it to the original heatsink.  I re-assembled the instrument cluster back into the car, re-connected battery and turned on the ignition and guess what ... it still wasn't working.  In fact nothing had changed - the problem with the warning lights and gauges was still there.

 

After a lot of head scratching and a lot more internet seaching, I chanced upon this post:

http://www.methodbook.net/electronics/polo.html

 

It seems I had an almost identical problem to the author of that page.  I say almost identical because he was also getting a discharged battery, but I was not.  Anyway he describes what he did, and basically I did the same thing - fitted a "shunt" wire to the instrument cluster circuit board to bring power directly from the live feed to the voltage stabiliser.  After refitting the instrument cluster, it now works fine.

 

So it seems the root of the problem was a broken connection within the circuit "board" which is attached to the back of the instrument cluster.  Actually it's not a board as such.  The printed circuit is embedded within a flexible plastic sheet, and sort of wrapped around the back casing of the instruments.  It's not readily repairable.  I guess it is deteriorating over time.

 

Anyway my repair seems good, it has been working fine for a couple of weeks so far.  Thanks again to the people who responded to this post.  And to the guy who wrote the blog I mentioned above.

 

On 28/07/2019 at 13:31, andrew_jo said:

Thanks for the comments you posted.  I have actually now fixed the issue. In case it's of any use to anybody else, this is briefly what I did:

 

First I searched around for a suitable voltage stabiliser.  That took a long time but I finally I figured out that I could use the same voltage stabiliser that was detailed on this page: www.cabby-info.com/gauges.htm.  From that page, I got the "Type" of the voltage stabiliser, and then I located a replacement of the correct type (KA7810AETU) on Ebay.  I ended up buying this one:

https://www.ebay.co.uk/itm/ON-Semiconductor-KA7810AETU-Voltage-Regulator-1A-10-V-3-Pin-TO-220/173386050782?epid=9021013911&hash=item285e9d2cde:g:JPEAAOSw5KFbNmV4

 

Then I removed the instrument cluster from the dashboard.  This was straightforward, but slow-going because obviously there wasn't much physical wiggle room.  Once I had removed the instrument cluster, I located the voltage stabiliser and removed it.  It's not soldered in, just push fit.  I removed it and tested it.  It actually tested fine.  But I assumed my test must have been flawed, or the voltage stabiliser was only working intermittently, and I went ahead and fitted the new one I had bought.  I also tested the new one before I fitted it, and it was also fine.  To fit the new one, I needed to bend its legs into the correct position, and break off one of the plastic locating tabs on the instrument cluster.  Eventually I was able to fit it and attach it to the original heatsink.  I re-assembled the instrument cluster back into the car, re-connected battery and turned on the ignition and guess what ... it still wasn't working.  In fact nothing had changed - the problem with the warning lights and gauges was still there.

 

After a lot of head scratching and a lot more internet seaching, I chanced upon this post:

http://www.methodbook.net/electronics/polo.html

 

It seems I had an almost identical problem to the author of that page.  I say almost identical because he was also getting a discharged battery, but I was not.  Anyway he describes what he did, and basically I did the same thing - fitted a "shunt" wire to the instrument cluster circuit board to bring power directly from the live feed to the voltage stabiliser.  After refitting the instrument cluster, it now works fine.

 

So it seems the root of the problem was a broken connection within the circuit "board" which is attached to the back of the instrument cluster.  Actually it's not a board as such.  The printed circuit is embedded within a flexible plastic sheet, and sort of wrapped around the back casing of the instruments.  It's not readily repairable.  I guess it is deteriorating over time.

 

Anyway my repair seems good, it has been working fine for a couple of weeks so far.  Thanks again to the people who responded to this post.  And to the guy who wrote the blog I mentioned above.

 

A very comprehensive post, i have the problem with the gauges, but not the alternator or the dash lights.

 

I guess seeing as the guy last visited in 2019 we won't be reading this, do we think he had a Mk1 style cluster or a Mk2 facelifted style cluster? I've recently discovered my gauges come back if i clout the top of the dash...

https://brickwerks.co.uk/product/voltage-regulator-t3-t4-lt1-caddy-1-instrument-panel/

It looks like this

 

https://www.cricklewoodelectronics.com/7810.html?gad_source=1&gclid=EAIaIQobChMIzvPtxPnghwMVtY5QBh399C-sEAQYASABEgJIT_D_BwE

 

This is what he thinks will replace it. I'm going with the one from Brickwerks, it's already ordered.

Sorry mr brightside, the polo was sold a few years ago so I no longer have access to it. I'm afraid I don't know whether the instrument cluster was Mk1 or Mk2 style. Maybe if I saw them next to each other I might remember which one it was, but hopefully when you replace the voltage regulator it will fix the problem regardless. Hope you get it sorted.

OK so here's what to do if you have my problem- ideally nothing, just live with it. The clocks have a motherboard into which each dial inserts by way of a header; this is the most likely site of my poor connection. To get to the voltage regulator you have to completely strip the motherboard of all the dials and remove it from the housing, which is a very delicate job, some of the tracks are tiny. When you take it to the car to power it up and test the regulator you get no voltage readings, then the tracks start to fry off the board and smoke rises. You spend the next hour replacing the tracks for which you will need:

Telephone wire cores

Craft knife to trim the blown tracks

Low wattage soldering iron with pointed tip

Small gauge solder

Acrylic lacquer to tropicalise the board afterwards

 

I was fortunate to have a usable set of clocks left at the end. It might not fry with the dials fitted, best option is a new motherboard if it doesn't work after you have inspected the headers; like i said they are a likely point of a hi-resistance connection.

 

Ouch.

Speedo is mechanical, but rev counter is electrical. I guess it has internal resistance that limits the current.

Fuel gauge, coolant temp guage too. 

Update on the issue of fuel/temp gauges malfunctioning.

Putting contact grease on the gauge unit pins that insert into the headers on the cluster PCB seems to solve the issue. No matter how many times i clean the pins it keeps happening. More importantly i am now convinced that this issue affects the blue temp sensor supply voltage. Since applying contact grease to the pins as described the tickover characteristics are totally different, and for some reason the ignition timing tested as being 5deg too late. I put it into service adjustment mode and corrected this. It's impossible to verify these proposed supply commonalities using the drawings in the Haynes.

Did you replace that voltage regulator 3 pin thingy too?

 

A modern 7810 regulator needs 12.5v in to produce 10v out so if your alternator brush pack or battery or engine earth straps are in bad way I guess it could brown out. (New alternator regulators spec at 14.2v).

 

And the contact grease is helping with lower resistance maybe??

 

7810 is different pin out than obsolete OEM according to Brickwerks.Outer pins swapped so fit upside down is their suggestion. 

 

 

 

 

 

Edited 19 December, 20241 yr by dvderlm

Resorted to hardwiring the temp and fuel gauges now, using contact grease worked for quite a while but I'd be refreshing it every 6 months. When the gauge readings started looking iffy it also began stalling at lights etc. Which adds weight to my theory that the blue sensor supply is also affected by voltage drops in the black sensor circuit.

On 19/12/2024 at 21:06, dvderlm said:

Did you replace that voltage regulator 3 pin thingy too?

 

A modern 7810 regulator needs 12.5v in to produce 10v out so if your alternator brush pack or battery or engine earth straps are in bad way I guess it could brown out. (New alternator regulators spec at 14.2v).

 

And the contact grease is helping with lower resistance maybe??

 

7810 is different pin out than obsolete OEM according to Brickwerks.Outer pins swapped so fit upside down is their suggestion. 

 

 

 

 

 

No I didn't change it in the end. I was trying to test it with the meter when the tracks started blowing off. The burnt track can be seen in the image, I think its related to the warning buzzer. I wanted to test everything first before fitting so I could verify which way up the new regulator from brickwerks needs to go.

Not that anyone will be attempting this job, but I thought it wise to keep the heat on the gauge pins to a minimum. Soldering the pins direct to the contacts would need a lot of heat and risk damage to the gauge internals. I used a 12v iron on a 10v supply and kept the work small scale.

On 08/06/2025 at 08:29, mr brightside said:

Resorted to hardwiring the temp and fuel gauges now, using contact grease worked for quite a while but I'd be refreshing it every 6 months. When the gauge readings started looking iffy it also began stalling at lights etc. Which adds weight to my theory that the blue sensor supply is also affected by voltage drops in the black sensor circuit.

Hasn't worked. Presumably because the original connection is still in the circuit in parallel.

No option now but to change the regulator and just refit the gauges as normal, can't be sure without testing though so will have to try getting the motherboard powered up without it going up in smoke. Problem is you can't access the regulator with the clocks assembled, so the gauge needles will be unprotected with voltage applied. I'm going to need a cunning plan, my lord.

Edited 10 June, 20251 yr by mr brightside

Replacing the electrolytic capacitor* next to the ITT chip might be a useful thing to do, and any other similar caps. Little chance of them still being anywhere near in spec after all these years, I'd guess. Respect polarisation.

*47u 16V written on top of it.

9 hours ago, Pete1 said:

Replacing the electrolytic capacitor* next to the ITT chip might be a useful thing to do, and any other similar caps. Little chance of them still being anywhere near in spec after all these years, I'd guess. Respect polarisation.

*47u 16V written on top of it.

Is RS as good a place as any to buy the caps?

Stripped it out again tonight to make a shopping list. 47uf 16v x 2, 100uf 16v x 1. I already have the regulator.

The regulator cannot go upside down, the heat sink will not contact properly and the whole assembly will be too fat with the spacer bush fitted. It has to go the right way up and be wired accordingly.

9 hours ago, Pete1 said:

Replacing the electrolytic capacitor* next to the ITT chip might be a useful thing to do, and any other similar caps. Little chance of them still being anywhere near in spec after all these years, I'd guess. Respect polarisation.

*47u 16V written on top of it.

Pete is that the -ve symbol I can see printed on top of them?

24 minutes ago, mr brightside said:

Is RS as good a place as any to buy the caps?

Yes.

Measure physical dimensions including space between leads/pads, and choose ones that are going to fit without too much bodgery.

If you're curious about how well/sick the old ones were, message me about sending them for testing.

https://uk.rs-online.com/web/p/aluminium-capacitors/0571757

Will this do? They are quite a bit smaller due to not being old hat.