Datsun Roadster Forum-311s.org

I'm hoping there are some electrical wizards out there that can explain this issue and suggest a fix.

I have converted my gauge VR using the stealth tip in the tech wiki.

If the key is on, but car isn't running, I have no fuel or temp gauge. If I touch my multimeter to ground and the 12v in of the VR, somehow that turns it on, and the gauges will work until I turn the key off. Then I have to "excite" it with the multi meter when I turn it on again.

If the key is on and the engine is running, the gauges will only work while I'm touching the multimeter to the 12v in lead. As soon as I stop touching, gauges die.

I am stumped as to what's causing this and how to fix it. It is very impractical to drive around with a multimeter attached to the VR.

Any ideas?

It sounds like the VR not grounded sufficiently to either the VR can or to the car itself. Make sure the plug is seated completely on the LM7808 VR and that the Common prong as shown in the pin out, is grounded well to the can. Then, make sure the can is well grounded to the car. If that doesn't work, I'd try another LM 7808.

I agree, sounds like a poor ground. The case of the OEM regulator is ground & depending how you grounded the Ground pin of the regulator chip, it could be the physical grounding of the reg can or the wire connected to the chip ground pin that needs to be grounded.

Peace,
Pat

Solved!

I thought it was ground at first, because that's always my first suspect. I spoke to Dave Premo and he told me that I have the "in" and "out" wires reversed. Well, Dave knows his stuff. Swapped the wires and both gauges work all the time now.

Thanks, Dave!