67-8 Instrument cluster

[shelbydoug]

I was just working on my cluster and it never occured to me (that I recall) that the mounting posts and the sensor connections to the gauges are the same (fuel & temp). Can someone explain to me how that design works without grounding those gauges out?

[Coralsnake]

No clock?

I think those gauges are groundwd through the harness?

[shelbydoug]

No clock?

I think those gauges are groundwd through the harness?

No clock. Vacuum gauge. Who cares what time it is? Dam thing never worked right anyway.

I still don't understand how the gauges work without grounding out the way they are mounted.

[Chris Thauberger]

The two mounting posts are the positive and negative connections for the gauge.

Current from the sender passes through a resistor that wraps around bimetallic strip. The bimetallic strip is hooked up to the needle of the gauge through a linkage.

The bimetallic strip is a piece of metal made by laminating two different types of metal together. The metals that make up the strip expand and contract when they are heated or cooled. Each type of metal has its own rate of expansion. The two metals that make up the strip are chosen so that the rates of expansion and contraction are different.

As more current passes through the heating coil, the bimetallic strip heats. As the strip heats, it deforms pulling the gauge from left to right.


Pictures below are of an oil pressure gauge but is the same basic design as fuel and temp. Bimetallic strip is highlighted in yellow.



Notice the shape of the bimetallic strip in the first and last sets of pictures.












Chris

[shelbydoug]

Thank you for the explanation of the gauges operation but if both posts are connected by grounding them through the case, how is there a positive and negative terminal.

Your illustration shows how I would understand the gauge to function but those terminals are also used to mount the gauges to the the instrument panel and have no insulators to keep them from grounding.

Look at how they are mounted.

[68stangcjfb]

That rectangular strip under the nuts is an insulator. If I remember correctly, there is another one between the gauge and the housing on the other side to keep the gauge from touching it.

[2112]

Isn't the bezel/panel non-conductive plastic?

[68stangcjfb]

Yes. But the rear cluster housing that holds all the gauges and lights is metal.

[2112]

Yes. But the rear cluster housing that holds all the gauges and lights is metal.

Ah, should have reread the original post

[Chris Thauberger]

Thank you for the explanation of the gauges operation but if both posts are connected by grounding them through the case, how is there a positive and negative terminal.

Your illustration shows how I would understand the gauge to function but those terminals are also used to mount the gauges to the the instrument panel and have no insulators to keep them from grounding.

Look at how they are mounted.

Look closer

That rectangular strip under the nuts is an insulator. If I remember correctly, there is another one between the gauge and the housing on the other side to keep the gauge from touching it.

Correct-a-mundo.

[shelbydoug]

That doesn't insulate the stud where it passes through the metal housing. The studs should have insulating bushings on them and they don't.

That's alright. You are just confirming that the studs should not be able to ground out to the housing.

[68stangcjfb]

Take the nuts off. You will see a big rectangular cutout under the insulator. The studs cant come anywhere near the housing.