Today I made a quick run into town in my ’77 F100, 302, automatic, stock, when I noticed something odd.

I’d gone about 15 miles into town, made a quick stop at the market and had just started coming home when I noticed the temperature gauge was pegged all the way hot.
My first thought was, “oh, crap, what now?”, but then I noticed the oil pressure gauge was also pegged to the far right (almost that is, but outside the ‘normal’ range and higher than I’d ever seen it).
While trying to think of something that would be causing both the temperature and oil pressure gauges to both ready abnormally high at the same time, I noticed my fuel gauge was also pegged to right. Knowing I had between ½ - ¾ of a tank, I figured something must be going on to make the gauges read wrong.

I pulled over, stopped the engine and sat for about five minutes hoping whatever was going on would ‘reset’. Started back up, but all three gauges immediately went to the maximum reading (needle sweep seemed like a normal start-up; nothing abnormal in the speed and no other odd behavior like jerking or hesitating, or plunging then climbing).
Since the truck seemed to running ok, I decided to see if I could at least make it home, a drive of about 12 miles from where I was.
Everything seemed to be fine and about four miles into the drive back to the house all three needles suddenly dropped back into their normal, expected, range.
For what it’s worth, I have the 5-gauge cluster: oil pressure above fuel gauge on the left, speedometer/odometer in the center, and ammeter (correct name? It’s the D – C, ‘charge-discharge’ meter, not a volt meter) above temperature on the right.
The ammeter stayed dead-steady in the center throughout the whole event. Nothing else seemed to misbehave, either: headlights and dash lights steady – no flickering, engine ran as normal, nothing else odd.

Any ideas as to what would cause three of my gauges to temporarily misbehave?
This is the first time I’ve noticed this, and I’ve had the truck for just under a year and have put probably 8-10K miles on it.
Other than some odd grounding issue somewhere that I’ll probably never find, is there anything else I should be investigating? I’m a bit stumped on this.

Thanks,
Raxx

 

 

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 // Myriad 1971/79 FoMoCo Passenger Cars.

When this puppy fails, it affects the fuel, temp and oil pressure gauges. The gauge needles may peg, or do the "hula" .. swing wildly back/forth on their own.

 

Thank you, gentlemen!
My symptoms sound exactly like a bad/failing ICVR. Off to the local parts store.

I swear this site is a godsend. I don't know how long, if ever, it would have taken me to figure this one out.

Thanks again,
Raxx

 

 

 

If the gas gauge drops to zero, you most likely have a break in the wire between the sender & the gauge cluster plug, or the connection at the sender is a little flaky.

 

 

The ICVR only affects the fuel and temp gauges if the truck has an oil WARNING LAMP.

If the truck has an oil pressure GAUGE, the ICVR affects it and the fuel/temp gauges.

 

 

The oil/amp warning lamps were standard equipment, the oil/amp gauges were optional.

The ICVR is the same for 1971/86 trucks (1971/91 Econoline), but it doesn't affect the oil warning lamp because it uses a different sender than the oil pressure gauge.