Earth resistance

In that case there was probably a voltage on the two terminals you were measuring

-- Malc

Try & find the next connecter back in the loom & see if the current through the diode burnt it.

That's just *slightly* relevant information...

There's all sorts of things on there could have blown with reverse polarity, even if a fuse did go to protect them eventually. The voltage regulator is one - check between ground and the output pin when the battery is connected - it's probably a 12V regulator so you should be getting a steady 12V if the battery is giving it the normal 13.5V+.

Right. Here's a load of background info:

Battery charged backwards, clocks stop working.

I assume some part of the clocks must be dead, so I rip apart the clocks.

I buy a second set of clocks. Still exhibits same faults.

I buy a third set of clocks. Again, same faults.

It's looking very much like it's not the clocks at this point, and so I'm thinking it must be the wiring. It's as if the computer chip at the bottom of the wiring diagram has no idea that the ignition is on or the car is started - no flash of the oil warning light before the key is turned etc. Pin 11 is the constant live to keep the time on the clock and memory for the MFA, and leads to fuse 21, which is the one that usually fixes the MFA computer if it's playing up. Pulling and reconnecting fuse 21 doesn't fix it now... Pin 13 is switched with the ignition, but I can't see how it can't be getting through to the MFA chip on two different sets of clocks.

Here's a complete pin out of the clocks taken from the GTI Club:

1 Outside Temperature 2 Coolant low level sensor 3 Ground 4 Stalk Switch pin 4 5 Stalk Switch Pin 1 / Ground 6 Stalk Switch Pin 3 7 Cruise Control / CIS 8 High Oil pressure switch 9 Low Oil Pressure switch 10 Rev Counter 11 Digital Clock power 12 Dash and Digital Clock lighting 13 Power 14 Not used 15 Stalk Switch Pin 2 16 Alternator Warning Light 17 Oil temperature Sensor 18 Not used 19 Outside Temperature 20 Not used 21 Fuel Gauge 22 Not used 23 Coolant Temperature Gauge 24 Direction Indicator lamp 25 Main beam lamp

From my meddling, it seems like this pin out data is correct.

Voltage reg should be between 9.5 and 10.5V. It puts out something around

9.95V. The only other faults I can think of off the top of my head is the unusal readings on Pin 5, which I've not had chance to check over yet.

Have you got access to any other Glof to test any of the clocks?

Could any of the external bits (sensors etc.) be blown and mucking up the chip? Is it possible to pop the (presumably crimped) connector pins out of the socket to cut out as many as possible and see what happens?

Could the replacement clocks be suffering from the same reverse charging issue? - if it happened once it could happen again...

I've tried them in a Driver, and they worked less than they do in my car, but he was using VDO GTI clocks and these are Motometers. I could really do with another GTI of the same spec to try and eliminate the clocks completely.

None of the sensors are very complicated, which is why I'm a bit stumped. Only thermistors and pressure switches that feed into the computer. The more complicated sensors - speed sensor, vacuum sensor are on the flexiboard that's part of the clocks.

Nope. They've only been in the car for testing purposes.

Looks like it's either the wiring or the stalk that's kaput then...

I was meaning before you got them... do you *know* they work?

I've been caught out replacing something with an already-duff spare before now.

Ah. No, I don't. I really could do with checking they work, but it seems unlikely that 2 would turn up with exactly the same fault.

Sods law.

I'd expect on a German car any true earth connection to have a brown somewhere among the colours. Greys are usually lighting related.

I went back out after posting that and I'd got it wrong. Twas brown...

Fix the black probe firmly to a known to be good ground, set the meter on DC voltage on a range higher than 14v. Now turn on the item which you think might have a problem and touch the red probe to any of its ground connections you think might be suspect. Any voltage read on the meter higher than 0.25v may well indicate a poor earth.