MetalEd

As I understand it, the sensor sending units complete the grounding circuit.. I've been working on the electrical (fuses, dash bulbs, reconnecting horn and radio).
I have pulled out the instrument panel on my 1964.5,(electrical still connected) I haven't put them back in since the temp. and gas climb all the way up when I turn on the car. So both gauges must be grounded, sending false sensor signal. Do they need to be installed in the dash to insulate them, maybe I am shorting it out by touching the housing or something against the metal dash? Since it is both gauges showing signs of grounding, it must be the instrument cluster that is grounded? (one ground goes to the engine, the other to the gas tank) Or is there something else that could be grounded that would affect both? (fuse block?)

JMD

Chances are the wires that run to the sensors are grounded out.

Yep, a short anywhere on the negative side of the guages will cause the gauge to go clean to the top. This applies to TEMP, OIL, and FUEL.

MetalEd

If I place the gauge housing in the dash, and align it correctly with the mounting holes, the gauges will drop and read correctly. I am thinking that the housing needs to be grounded or I am hitting a loose connection that affects both gauges. Could it be grounded through the speedometer cable, that is the only thing I haven't re-connected and appears to touch the gauges when I mount them.
If the gauges are out of the dash, (maybe not grounded), then the gauges climb all the way up, like they are grounded on the sending unit post.
Maybe it has to be grounded in order for the voltage regulator to work properly and the mounting and/or speedometer cable grounds the unit?

MetalEd

It sounds like the problem, except I did nothing to either sending unit or gauge and now they are giving the same error.
The gauges worked before I removed the housing, I didn't touch anything that would go to the sending units (ground) of either unit. And since they both go directly to their sending units, (opposite ends of the car), I couldn't have grounded BOTH of them out.
I followed the grounds for both units out of the pass. comp., nothing wrongs, no breaks or loose connections.

That's what is odd. I change the fuses, bulbs in the instrument panel. The bulbs still don't work, which I attribute to a bad headlight switch.
My thinking is that the instrument panel needs to be grounded.. If it is placed back in, very precisely, the mounting holes aligned the gauges drop to their normal operating ranges. I just want to make sure this sounds like the problem and I don't have a weird short behind the panel. I can repeat this over and over... If the instrument panel is placed back in the dash, they both start working normally (appears to), but if they are misaligned even a millimeter, they rise to full.
It's hard finding answers since this is the 64.5 (generator) and even the 65 is wired differrently.

tx65coupe

I had a similar problem and it was the instrument cluster voltage regulator. My original one is the only one that works half way decent. All the replcement ones were crap.

My Dad ended up making an electonic one from radio shack parts.

Both NPD and Paddock have the solid state one.

If you illumination doesn't work did you try turning the dimmer. Mine has an issue with that. If the dimmer is all the way up the lights don't work, but if it is turned down a hair they work.

JMD

I am at a loss as to why these circuits would want a ground on the panel itself, but I never claimed to know everything!

Stick a ground wire (permanent) on the panel to a GOOD body ground and see if it handles your problem, if so then problem solved!

I am big on ACTUAL ground WIRES, these can save TONS of Bull Ship.

MetalEd

I've traced the dash lights problem to the Light switch. it controls the instrument panel lights brightness/dimmer. It's very common for it to go out completely or only work in one position (as yours does) without affecting the headlights.
I'll be replacing mine shortly.. If your dash lights go out, just keep this in mind before messing with other wiring. Easy to test!

MetalEd

I know the panel backing is a ground, since it is the rest of the circuit for the dash lights (each bulb only have 1 wire each and are mounted to the panel backing for the ground).

I am not sure exactly what is going on, If I install the Speedo Cable and then mount it complete with screws, then both gauges work properly.

I found something in one of my manuals that says if BOTH gauges are incorrect in the same direction (too high or low), then it is probably a faulty or short to ground on the voltage regulator!
This sounds like exactly the problem I am having... maybe shorting the voltage regulator to ground when opening it up? Anyhow, I found how to diagnose it with the voltage meter.. So I will have to open it up again and check it out! Even though it is working perfectly right now, I just need to know.. I don't want a short to ground going undiagnosed!
Thanks for the help!

kalli

just like JMD says (and you assume) if the sensor wire hits ground the gauge will raise all the way to peak.
But it's not a valid test with the gauge not in place. With the gauge out of car (screwed into dash where the hosuign gets ground from chassis with that little flap at bottom) the gauges will do whatever they want and the lights (the lights that illuminate cluster) won't work either. only the idiot lighs will work as they bring their own ground (2wires at bulb)

Kalli

MetalEd

That's exactly what seems to be happening, I also found a blurb that said the instruments will not work correctly out of the dash since some early systems require the ground from being installed in the dash. I'm not sure of the "flap" you are speaking of since I have been looking for a grounding wire, but I will be sure to look this time around!
I'm going to install a few jumper wires to the voltage regulator and the gauges, drop them through the dash (insulated wires of course), then install the instrument cluster. test leads, since my probes are not long enough and I don't want to short out anything else accidentally! If it does require this ground, like I believe, then I will get exact readings on my voltage meter,
Thanks for everyones help, I've learned more about the car's electrical system than I ever thought I would!