dashboard wires go where?

[greenv8s]

Where do the dashboard instruments get their power and earth from?

The voltmeter has started dipping wildly when I turn on small loads like indicators and brake lights, and I'm trying I'm trying to work out why. With everything on it goes as low as 9v which is clearly wrong! I'm pretty sure it's a wiring fault but so far I can't see where the instruments get power *or* earth supplies which is making it a bit difficult to track down. I've got my eyes on that big 20-way connector down by the ECU, am I on the right tracks?

I've looked for an earth on the passenger side outrigger (there is one, and it's fine, but the instruments don't earth through it) and under the tunnel (there's a body mounting bolt, but no connections to it). There must be a chassis earth somewhere under the dash, any idea where?

BTW I've confirmed the battery voltage is fine, the feed out of the ignition switch is fine (dips a little under load but nothing like the dip shown at the voltmeter), all the fuses are OK, no obviously broken wires in the mess of wires in the passengers footwell(I'll resist the temptation to call it a 'loom'). I haven't tried pulling fuses and connectors apart to see which one feeds the dashboard, but I guess that might be the next step.

On the bright side, while I was looking into this the intermittant fuel pump problem I've been trying to track down over the last few weeks finally showed up enough for me to track it down with a meter. It seems that I have an intermittant break in the wire from the fuel pump relay to the pump. It's going to be a pain to replace, but at least I know what the problem is now! As far as I can tell, this isn't related to the voltmeter problem though.

So, instrument power and earth, any ideas where they come from?

Thanks for any help.

Cheers,
Peter Humphries (and a green V8S)

[tvrgaas]

Pete
Not much help but on my S1 the instrument power IS off the indicator fuse and the return IS via the NSF wheel arch. It failed the MOT once due to slow indicators, yes I was please too, it was the NSF chassis return. It was dropping a volt or so at this point.

Two hints which may help, the cigar lighter is off the same circuit, so you can use the multimeter here to check the voltmeter reading. I found probing battery terminal to cigar lighter (etc) will tell you which side has the voltage drop.

Obviously be careful when touching the battery terminals, and make sure the mulitmeter is on volts!

Physically where the wires go? I don't know, I've looked behind the dash once, that was enough, I thought "if it ain't bust, don't fix it!" and left it alone

David

[shpub]

Pete

TVR have a habit of bringing seperate earths to the dahs via the main dash loom that ha all the other signals. This is derived from the chassis or engine earths.

You might want to run an temp earth first to see if this solves the problem before chasing things further as it could equally be a corroded/broken power wire through the connector as well.

steve

[keirangrogan]

shpub said: Pete

TVR have a habit of bringing seperate earths to the dahs via the main dash loom that ha all the other signals. This is derived from the chassis or engine earths.
steve

Yep, When I had my dash fire, I found that the intruments are earthed through the main loom onto the chasis on the passenger side in the engine bay just below the washer bottle.