Fuel & Temp gauges not working

[jwex]

My fuel and temp gauges have stopped working properly.(VR commodore) By "properly" I mean the needles now move only about a mm whereas the fuel used to read correctly (full range) and the temp would sit happily on about a third of max.

I read in the forums that the voltage regulator often develops dry soldier joints so I resoldered them even though an ohm meter suggested the joints were good. Retested with the meter, put back in car and no change.

Thinking that the voltage regulator was possibly faulty, I have now tried two different instrument modules from the wreckers with no luck.

What else could it be?

Is there a way of testing the voltage regulator?

Is there a way of testing the gauges?


How do I get to the fuel sender unit? I can't find anything under the back seat or the boot mat.

I'm desperate for some help here as it's costing me $20 in juice to drive to the wreckers and back each time.

Thanks

[88GreenVN]

Have you had the dash plugs out for any reason? If the 3rd plug - drivers side is upside down the temp gauge will not work.

It should have an orange white wire top left (second position in) as you look at it from the drivers seat.

[jwex]

Thanks for the reply. If you mean the 3 plugs that fit into the 3 cavities at the back of the dash module, I haven't touched them.

[88GreenVN]

If you have tried 2 other clusters, soldered up your voltage regulator and not touched the plugs - it would have to be the voltage cumming from the senders or the earth. Would seem sus that both the temp and fuel senders fail together. So I'd trace out the earth side of things on the dash wiring. Has there been any changes to the car of late - any one fiddle under the dash?

Do the speedo and tacho work correctly? (assumed the do)

[jwex]

Thanks for reply,
No one has been under the dash except for me trying to solve the problem.
the tacho and speedo work perfectly. I was assuming the earth to the dash is OK because the backlights work perfectly but I'm willing to try anything. How would I go about tracking a bad earth problem?

[88GreenVN]

I'd check the connector that hooks up to the fuel pump. It's a flat plug with 3 wires I think - up plug it and see if it's corroded. You will be working under the car between the diff and the tank. Watch your eyes for dirt hey.

If the sender wire is corroded the voltage will be wrong - being sent to the gauge.

Just dont seen right that both senders pack it in at the same time tho.

[88GreenVN]

Hmm - also you could check the main dash plugs to see if all the lugs are home in the connector as they should be - may have been played with before you got the car....

[jwex]

Thanks,
Will check that tomorrow. I've just tested the gauges with two 1.5 volt batteries hooked up in series (3V) and they both seem to be ok. (Moved a lot further than they have been) Any idea how to test a voltage regulator with the instrument module out of the car?

[88GreenVN]

I dont know of any way to test them out of the car. If you have soldered up the voltage regulator already I'd say the problem is getting voltage to the gauges.

I test all the VN/VP clusters I work on in my car to see if the gauges work as they should. VS - I'm still working on a test bench setup

[jwex]

"I test all the VN/VP clusters I work on in my car to see if the gauges work as they should."

How do you do that? I can't get to anything after the dash cluster is in.
Regards John