Fuel and temp gauges not working

[Minderbinder3]

Original gauges on my ‘66. Alt, Speedo, and Oil pressure gauges seem to somewhat work. The Speedo bounces pretty good but puts me in the ballpark.

Temp and fuel gauge don’t move at all. I would really like the fuel gauge functioning.

Where do I start?

 

[Broncobowsher]

Well you have a good start. If the oil pressure is working, that confirms power to the guages and the IVR is working.
Temp sensor is generally easy to check, find the sending unit and take the wire off and ground it. That should make the temp gauge rise to hot. If the engine has been replaced, or even just the sending unit for the warning light, the gauge will read cold until overheated and then the gauge will peg.
Fuel gauge, often a big issue is the selector switch on dual tank Broncos. Sending unit not being grounded, or a failed sending unit ranging from rust in the tank to a float that was made by the same people who made the Titanic (float sunk to the bottom of the tank) The test generally involve grounding the sending unit wire and see if the gauge goes up. If it does, start working back toward the tank. If it doesn't start working toward the gauge. The gauges are nothing more than a heating element and a thermostat spring that moves when it gets hot. The needles can get stuck in place, heating elements burn out, bad connections. and the list goes on as you move from the gauge toward the sending unit.

 

[Steve83]

Original gauges on my ‘66.

What about the wiring?

Alt, Speedo, and Oil pressure gauges seem to somewhat work.

It's pretty surprising that the ammeter appears to work, but it's not electrically connected to the other gauges. The speed isn't electrical at all.

The Speedo bounces pretty good...

That indicates something is bent, or there's some debris inside it.

Temp and fuel gauge don’t move at all. ...
Where do I start?

I'd start by looking at the wiring on the front of the cluster. Each gauge has its own wires, so any single gauge can go dead if either of its wires is loose. But the oil, gas, & temp gauges share the ICVR output, so if one of those gauges works, they all should. To test a gauge & its circuit, simply short the sender wire to ground with the key in RUN. The gauge should peg within a few seconds. If not, either the gauge is unplugged or dead, or there's a break in its sender wire. Scroll sideways on this diagram to sections 12-14.

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[B RON CO]

Hi, as for the speedometer, I would remove the whole cable from the Bronco, and then pull the inner cable out of the housing for cleaning and lubrication. Good luck

 

[Broncobowsher]

Sticky (not spinning smoothly) speedo cable makes for a jumpy speedo. Not always the cause of being jumpy, but often.

 

[Minderbinder3]

Upon further inspection none of the gauges work except the Speedo, which I did clean and lubricate but have not tested yet.

I am not really able to inspect the wiring behind the cluster due to the tight space. Is there a way of removing the cluster without having to disassemble the dash so I can check it?

 

[BroncoLew]

Cluster is held on by 4 screws. Disconnect the speedo cable and then then take out the screws it will come down. Bring it down slowly and have some tape to mark the wires as your remove them so you put them back.

 

[Steve83]

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Adding a multi-pin connector (or 2) makes it much easier to R&I because you don't have to disconnect each gauge & bulb.

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[gnpenning]

If you remove the driver's side air inlet you can see the back side from the engine compartment. Pretty easy to remove. Might help your view.

 

[Minderbinder3]

Dropped to gauge cluster and cleaned and checked all connections. Still nothing except Speedo and blinker indicators working. Even replaced the small bulbs and they won’t work either. All connections look good to newish voltage regulator under the hood.

Any advice now?

 

[Steve83]

Any advice now?

Post lots of pics.

 

[DirtDonk]

Even replaced the small bulbs and they won’t work either.

Two different issues. Gauge is not working and lightbulbs, not working or not related.
Is your cluster hanging there? If so, you need to run a ground wire so that it can be tested correctly. If that wasn’t done, hopefully you didn’t damage the instrument voltage regulator.

The lights’s not working are either:
1. Cluster not grounded.
2. Bulbs are bad.
3. Headlight switch is bad.
4. The smallest fuse in the fuse panel is bad.
5. The dimmer/rheostat in the switch, is not turned up to the right position. Turn it till it clicks and check again.

All connections look good to newish voltage regulator under the hood.

The main alternator voltage regulator has little to nothing to do with anything in your instrument cluster not working.
When speaking of the gauges and a voltage regulator, it’s commonly referred to as the IVR, or in Ford-speak, the “constant voltage supply”, and it’s attached to the back of the instrument cluster.

 

[Steve83]

...“constant voltage supply”...

Where did you read that? I've never seen "constant" associated with it. It's not constant, nor a supply. It's a pulsing switch that averages the same time off as on so that the average voltage is 6VDC because the instruments are carried over from older 6V vehicles. It's a self-resetting circuit breaker that's built to trip & reset over & over. The voltage supply is the battery. Seabiscuit's diagrams call it "Instrument Cluster Voltage Regulator" (ICVR) and some say "(C/V Unit)" below that which I assume means "cluster voltage unit".

 

[DirtDonk]

You know what it is, and I know what it is. But the very first thing I ever read it called was CVS.
I think it might have been in my first “66–73 Bronco“ Chiltons book.
But it’s a vague memory from almost 50 years ago. I’ll see if I can find reference to it.
For me “IVR“ and instrument voltage regulator came much later. Probably after the Internet forums started.