A buddy's son picked up his first vehicle... a 1981 F100 Custom with a manual transmission and an inline 6.

He is having problems with the gauge cluster not working... nothing works except the lights in the gauges. I would guess if all the gauges are not working it may be a single problem tied to all the gauges...

He said he has checked all his fuses and everything looks good.
I told him to bring it over and I will look at it.

Any ideas where I should start and some ideas of what to look at and what to look for ?

Any help is greatly appreciated. It would be great to save this young man some dollars on fixing his first truck.


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You are probably correct - the single point of failure is the Instrument Cluster Voltage Regulator. However, it is nothing like a real voltage regulator. It sits on the back of the cluster using what looks like a 9V battery's contacts. Here's a link to my album on how to build a proper replacement to fix the glitches these problematic things give us. Or, you can go to the salvage and get one that'll probably work. Sorta.

But, it could be that all of the senders are bad. You can test that by turning the key on and grounding the lead going to a sender and see if the gauge goes to full scale. Or, put a meter on the sender and you should see something like 12 ohms at full scale and 70 ohms at the other end.

 

Does the speedometer work?

 

no, speedo does not work.

All the gauges are dead. The back lights work on the gauges when the head lights are on but the gauges themselves do not work.



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Hmmm? The fuel, oil pressure and temperature gauges share the ICVR as pointed out by Gary Lewis. If you have an ammeter, it does not receive power through the ICVR, but rarely moves so much as to be noticed. However, the speedometer is mechanically driven by a cable, so is not related to an electrical issue.

Since it sounds like this truck is "new" to your buddy's son, I suspect that the previous owner has removed the gauge cluster, maybe in an attempt to sort out "something". The speedometer cable has to be loosened from the speedometer to remove the cluster. There is a spring loaded clip [of sorts] which must be pressed to one side in order for the cable to come loose.

Read the 2nd paragraph as written by Gary Lewis [above] to see if the senders are bad and that the gauges are receiving a signal. Then, check to see if the speedometer cable is loose.

Check these things and get back with us. Good luck!

 

Thank you for the replies !!

Is there a way to check the ICVR to make sure it is or is not working ??


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Sorta. You can't really put a meter on the output of the ICVR as it puts out a really, REALLY jagged wave that drives DVM's crazy. But, by testing the gauges via simulating their senders you are effectively testing the ICVR. In other words, if a gauge works the ICVR is working.

Having said that, ICVR's are notorious for changing in the middle of a drive, or several times during a drive. You can usually tell it has happened because the fuel gauge has gone up instead of down, but it is freaky when the temp gauge goes up all of a sudden.

 

My rule of thumb is to look at the three gauges affected by the ICVR output [fuel, temp and oil pressure]. If all three are on the high side, I attribute it to the fluctuations of the ICVR. In my experience, if temperatures REALLY get high, then oil pressure goes down.

 

I am going to try building my ICVR.

The local electronics store has this in stock :
AnyVolt Micro - Universal DC-DC converter steps voltage down and up
2.6V to 14V output voltage range
2.6V to 14V input voltage range
0.5A max input or output current at < 10V

but this is what is suggested in the link above :
Adjustable step down switching voltage regulator
Adjustable from 1.25 to 13V output using screw
1A output at 1.25 to 10V

Obviously these are different..... any idea if the first one that is available locally will work OR should I just order the one from the build online ??


Thanks !

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Half an amp isn't enough power. Each of the sending units is supposed to be 12 ohms at full scale. At 5.4 volts that is almost .5 amp for one gauge - and you have three. Granted you shouldn't have a hot reading at the same time you have the oil pressure pegged, but assume both of those are mid-scale and you have a full tank of gas - it'll pull a full amp. Don't cut corners it will bite you.

 

Why not just order one from LMC?

Part# 47-0894

Page 34

Fits 1980 - 86 F series trucks

Cost is just $29.95

Im sure $29.95 is cheaper than trying to fabricate up something on your own considering the time involved and the headaches if something is not just right.



Other question I have is the gear that is spinning in the transmission, are we talking about the drive gear on the output tailshaft or the driven gear which connects to the speedometer cable?

If its just the driven gear that is spinning which I think is most likely considering they are plastic, you shouldnt have to pull the tail shaft off to just pull the driven gear out and replace it with the same color gear.

 

If I remember correctly, the heavy duty regulator I spec'd in the IVCR instructions comes in at a bit less than LMC's version. And, it will put out a far, FAR more stable voltage than the LMC unit, assuming they built theirs like Ford did. That is a very poor design and I wouldn't want one.

Second, my understanding is that it is the drive gear that is spinning. Let's see what my says.

 

There was two different icvr's ford Ford's?

I wonder if mine is a heavy duty unit.

 

You can convert to a solid state IVR for about $16.

http://www.ebay.com/itm/REBUILD-ANY-CONSTANT-VOLTAGE-REGULATOR-DASH-INSTRUMENT-CLUSTER-INTO-SOLID-STATE-/181518224499?pt=Motors_Car_Truck_Parts_Accessories&hash=item2a43544c73&vxp=mtr

 

Plastic piece on the end of the speedo cable appears good and when spun by hand the other end of the cable that goes in to the speedo gauge spins.
The speedo cable and gear appear new.... figuring the previous owner bought a new cable to try to fix the speedometer and it obviously didn't work.


The gear inside the transmission spins freely if I stick a finger in there and move it.


This seems a lot more complicated than getting the dash cluster sorted out .... hopefully atleast one of these fixes isn't overly complicated.




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