Speedo Issues / Earthing Points & Wiring - Help Please

[Storm Guy]

Hi Folks - hoping some one can shed some light on resolving what now seems to be a non-responsive speedo - before I start pulling the main dash to check the actual speedo and rear connections.

Speedo was behaving erratic over christmas period, sometimes dropping to zero, then coming back to life on subsequent runs. Has now stopped - no speedo or mileometer, 10A fuse ok and other integral display leds work fine within the main dial, eg. battery symbol.

Thought I'd start by checking and cleanning up two the earths immediately infront of each of the door pulls.When doing so, saw that, on the passenger side, there was a thin braided copper earth strap (pic, marked F in diagrammbelow, and lower red arrow), tucked under wires, making its way forward towards the main dash (see upper red arrow). A gently pull revealed that it was loose and looked as if it had become detached from its source.



Questions are;
Do you have a similar small earth strap?
What this is supposed to be earthing - is it connected to the speedo/instruments?

The diagram below shows the build up of earth connections on each side. Thick cable = Drivers side A & B, Passenger, C,D,E.



Secondly - after pulling the bound wires up from the grommet that can be seen in the pic below, one wire was damaged. This black and yellow ((main & trace respectively) wire according to the Heath manual indicates it's the electric speedometer (?) - which may be the real issue. However on reparing the wire (cut/solder/heatshrink connection), cleaning and tightening earths (not that they were loose), a run out shows the speedo is still not mvoing from zero.

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The sensor itself may of course be another one to check - the area has been cleaned and looks to be ok. Think there is a connector also joining the wires from speedo to connector and connector to sensor underneath car - but need to still gain access to that - if it is at all possible with the drivetrain et al in the way.

Any ideas/thoughts please, ahead of me removing dash and replacing parts.

Thanks

[Storm Guy]

Thanks Guys...

Steve_D said:

I have a similar wire on my 97 Chim. It goes up into the windscreen pillar. I think TVR built a radio antenna in the top screen rail but I'm not sure as I have never see a co-ax cable coming out. That wire would be to create an 'Earth Plane' for the antenna.
Steve

Thanks Steve - Just for clarity - similar to wire F, ie the thin braided earth (and not the black and yellow wire) and assume it goes bang under the radio position and then heads left or right to to one of the pillars?

griffdude said:

.... Label everything & take pictures!!! Have you got a copy of the ‘bible’? The wiring colour decode might be useful.

Thanks, yep, have the Heath manual aka Bible, and have OCD re pics / labels

geeman237 said:

I’m afraid I can’t offer any help, but it might be useful if you stated what model/year your Griffith is as the instruments changed over time.

Tis a 500/1996.