Earth resistance

You should have zero resistance on any earth,. I think your "cheap" multimeter may not be 100% as you shouldn't have a negative reading for resistance,are you able to zero the meter?If so you might want to do that first..

Steve

50 ohm is far too high. Check again with the battery off though, just in case.

You should expect quite a way below 1 ohm, depending on the meter.

Better still,check for poor connections using volt drop,its better than using resistance..

Steve

Righto. Just had another play and using the continuity buzzer function of the meter there's a bit of stuttering. Looks like I may have found the fault...

For those with a better brain for electronics than me, here's the diagram of the clocks:

Pins 3 and 5 are earths - AFAIK 3 is the main earth and 5 is linked to the MFA (trip computer) stalk. The basic problem is that everything operated by the box of tricks at the bottom of the screen doesn't work - no computer, no rev counter, no oil pressure, no nowt...

Hopefully now someone will post and tell me I've cracked it...

And pin 3 is the dodgy one.

Most digital multimeters show -1 for infinity resistance - in other words an open circuit or no connection.

I bet you're measuring resistances with the car battery still connected. It's not advisable as you'll likely either blow the meter up or get negative or false readings if the circuit has volts on it or current is flowing through a connection.

If the meter zeros ok on the ohms scale sounds like there's some volts there.

50 ohms is far too high - I doubt it ever was a true earth connection. What colours on the wire?

Umm.. Pin 5 isn't connected on that diagram.

3 does look like it's an Earth, 13 the +V supply. Pin 1 is also connected to the Earth, so with the whole panel unplugged is there a link between 1 +3 (on the instrument panel, not the connector to the fuse box)?

Between 3 and 13 on the connector you should have the full battery voltage, possibly only with the ignition on.

Resistance is futile. You will be assimilated.

Steve

Disconnect the battery & do it again, the current flowing to earth from the cluster is confusing your meter. If you use the probes the other way round then the readings will change.

I think you've spotted it.

It isn't connected to the fusebox - it's connected to the MFA stalk

Yep. I have got a full pinout for the instruments, but it's not on that diagram.

Grey.

IIRC mine doesn't. It'd do it every time the probes aren't on anything.

By the way, the clocks started playing up after a battery charger was connected up in reverse. Several sets of clocks have exhibited the same faults, so I reckon it's the wiring. Am I right in thinking that the diode between pins 3 and 13 would have allowed basically an open circuit so it's likely the wiring's knackered somewhere? Or should it have munched a fuse?

If you're sinking a reasonable amount of current all the time you might have blown a diode short circuit, which would bugger up your resistance readings.

I'm testing the wiring with no clocks attached. The diode tests out ok on my meter.