Hi,

Thanks to Steve for referring me to the FAQ for my erratic speedometer problem.
I probably need to repair the speedometer, but the FAQ recommended checking a ground wire in the driver side foot compartment. Where is that wire exactly?
Any advice is welcomed!

bassmark2000@yahoo.com

Thanks for posting. I am trying to locate the ground under the drivers seat in my 95 960. Where did you find yours?

For 900's (seemingly all), the speedometer gauge ground (ground reference) is the brown/grey wire off pin 4 of the 14-pin connector behind the tach area of the cluster. This ground circuit goes through one of the large 53-pin connector blocks (not usually a problem area) at the driver side A-pillar, tucked up in the rats nest rearward of the hood release. This in turn goes to the ground rail on the underside of the electrical distribution unit (relay tray) in the center console which in turn goes as a black wire to the chassis ground rail at the right A-pillar behind the ECU (again, not usually a problem area). If the relay tray has been recently disturbed then it may well be worth pulling it to check the connection under the tray (pull off, clean up if dirty, crimp a bit if loose, reseat -beware of live wires under the tray). The FAQ suggests the terminal contact in the connector on the back of the cluster is a possible problem area (again, pull, clean, crimp as needed). Additionally, you may wish to check the sending unit terminal connections at the cluster. They're at the aforementioned 14-pin connector: pin 3 (brown/white wire, sensor +) and pin 5 (green/white wire, sensor -). Otherwise, suspect the speedometer gauge, sender, cluster circuit board or other areas as suggested in the speedometer articles in the Electrical: Instruments section of the 700/900 FAQ.

While I've got the manuals open I'll clarify the FAQ for 700 owners (at least those with later VDO or Yasaki clusters). The speedo gauge ground reference is the green/black wire off pin 11 of the 12-pin connector behind the clock area of the cluster. It goes to the left A-pillar ground chassis rail behind the kick panel (right A-pillar for RHD cars).
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Dave -940's, prev 740/240/140/120 You'd think I'd have learned by now

Dear Dave,

May this find you well. Given your well-meant warning about live wires around the relay block, it might be well to disconnect the negative battery cable clamp from the negative battery terminal, and put the clamp in a plastic bag. By cutting power to the entire car, this will, of course, slash risk of unintended damage while tracing the speedo ground wire.

The radio security code must be handy, to re-activate the radio.

Yours faithfully,

Spook

Dear Bassmark,

May this find you well. To answer your question properly, one needs to know which model (940 or 960) and the year.

It is probably more cost-effective to get a speedometer at a salvage yard, and have the mileage re-set, than it is to have repaired the factory-original unit.

APT Instruments, in Bloomington MN, charges about $60 to re-set a speedo. You'll need to send some documentation - e.g., a repair bill - to support your request.

Hope this helps.

Yours faithfully,

Spook

My model is a 940 and the year is 1991.

Panel ground on the 91 goes to the ground plane in the fuse panel, thence to the passenger side body ground plane just forward of the passenger (right) door lower hinge: remove the panel and you'll see it. I think this is likely not a problem, though: I suspect something in the panel circuit or the connector to the panel. The flex circuit board connections can corrode, leading to erratic results. I have had to remove the panel, loosen the connection screws on the back, spray a little DeOxIt beneath each one, and retighten. I've also had to look at the solder connections on the panel board too. More in the FAQ.
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See the 700/900 FAQ at the drop-down menu above right.

Dear bassmark,

May this find you well. I have wiring diagrams for 1993 and 1994 models. Fault tracing requires an accurate diagram. Another Brickboarder will surely be able to help.

Yours faithfully,

Spook