Hello everyone,
Here is the background for my question. Have a 78 F150 Ranger has 4 core rad.and a 351M with C6 in it and runs good but on occasion the water temp gauge runs up to 12 o'clock from its normal spot that is just out of the clear space before the lower line of normal. Thought it was the thermostat but then noticed the oil pressure gauge goes up about 1/3 higher at the same time. When the temp. gauge drops to its normal spot the oil gauge will follow after a couple min. Just to fill in more info the Amp. gauge has always been just on the discharge side even though I have put a different gauge in, in the past . The charge system when tested works just fine just no needle movement. My question is this, could there be or is there a portion of the circuit board that controls the reading on the two gauges - water temp and oil pressure - as well as there being a failure on the board that supplies the Amp. gauge... Had a 69 Rambler in collage and it had a solid state cluster and a piece fell out , turned out it was a wire wrapped piece that powered both fuel and oil gauge, it snapped back into its slot like a fuse and powered up the gauges. Thanks in advance for the solution to this on and off problem

 

There is an instrument voltage regulator (IVR) on the back of your cluster that supplies the gauges with about 5 volts. It is a small metal box that plugs in to the printed circuit like a 9 volt battery. A screw holds the IVR to the cluster body. The IVR is not solid state, it pulses the power off & on to roughly regulate the voltage thru a set of points. If the IVR were to act up, I could see it causing high readings. Does your gas gauge act up at the same time? Gas, oil & temp all work off the same IVR voltage. So, the gas gauge should be reading high the same time the other gauges do. You should be able to find a new IVR with a little searching. The cluster does have to come out to install the IVR.

The Alt gauges in these trucks are notorious for not working. They work on very low voltage, like .1 volt will move the needle. 1 volt is enough to peg the gauge. The smallest amount of corrosion will render the gauge inoperative. If you clean & polish every contact point on the Alt gauge & the PC traces it connects to, as well as the plug & socket for the cluster, the Alt gauge will work for a little while until a little corrosion comes back. You can test your Alt gauge when it is out of the cluster by using an almost dead 1.5 volt battery to apply power to the studs on the gauge. If the gauge is good, it will swing one way when power is applied. Reverse polarity & it will swing the other way. If it doesn't work you can take the gauge apart & solder two fine wires to the studs they are wrapped around. This will usually fix a non working Alt gauge, but it is delicate work.

There is a company that converts the Alt gauge to a volt meter, cost is around $50. The one thing I don't like about doing this is you have to cut your PC to install it. I don't like cutting good parts.But, you'll gain a more functional gauge.

I'm an AMC Rambler guy, they used a very similar setup to Ford to power the gauges.

 

Scottscott, Thanks for the info. on the cluster. I have had the cluster out before and cleaned all the contact areas on the main ribbon circuit were the gauges have the screw down clips as it were, also used a little dielectric grease on the threads. I also painted the plastic and replaced the bulbs with led so less heat in the cluster. I remember seeing the IVR and noticing the ribbon snaps onto it and the one screw holds it. Cleaned the row of contacts of the plug at the same time also. Have not been looking at the fuel gauge but since I rebuilt both tanks over a year ago, the main tank runs up to F but goes below E and still has fuel, the reserve tank starts well above F and is empty at E so maybe it is showing the problem with the difference in the two tanks. Just didn't maybe make a connection with the other gauges and the IVR
The 69 Rambler had the piece with the copper wire fall out and at the time - collage - didn't know it went up in the cluster, unwound it and pinned it to my room ceiling so my radio got great reception, only later after noticing the two gauges not working and buying one did I put 2 and 2 together lol Any idea of the cost of the IVR and if it can be gotten at the parts stores?

 

Scottscott,
The symptom of the water and oil pressure gauges acting up can last a day or two then go back to normal range for several days to weeks and act up again. The outside temp. doesn't matter but have noticed the problem most recently since its been cold here in AZ. Phoenix area... and the temp reads higher and the oil gauge was just noticed after watching them all during this .

 

Here's a NOS IVR on ebay. You can probably use these numbers to cross over to something a local parts store would have. https://www.ebay.com/itm/Motorcraft-...frcectupt=true

 

D1AZ-10804-A .. ICVR - Instrument Cluster Voltage Regulator (Motorcraft GR-513) / Obsolete ~ Available NOS & from auto parts stores.

1971/86 F100/350 / 1971/91 Econoline / 1978/86 Bronco // 1983/85 Ranger // 1984/85 Bronco II // Misc: 1971/79 FoMoCo Passenger Cars.

1980/88 Cougar/Thunderbird with mechanical cluster // 1980/89 LTD/Crown Vic/Grand Marquis & Lincoln Town Car with mechanical cluster.

1981/82 Granada // 1983/86 LTD/Marquis (Fox body midsized)