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I have a 1976 F-150 4x4 truck that has non-functioning gauges on the dash. No lights, no readings. I have spent a lot of time looking through other forums and trying to find answers, but I can't seem to figure out what's wrong with mine.
I do have a working light on the headlight/wiper side, as well as the HVAC controls, and the PRNDL. Headlights, tail lights, side markers, clearance markers and everything else works fine. My dome light doesn't work, not sure if that's related at all...
Every fuse in the block tests out fine. I have 12v at the INST PNL fuse, and I do have the "fasten seat belts" light coming on, so power is getting to the dash. I also have replaced the voltage regulator on the back of the dash panel with a new one.
I have noticed that my headlight switch is touchy, when you spin it the few dash lights that DO work will go on and off, as if the switch is corroded or something. And when they're off, there is no power to the INST PNL fuse (so they're tied together somehow?). So I have ordered a new headlight switch, but I doubt that would cause my dash gauges to have no readings, since they should work without the lights being on. Though it may fix the gauge bulbs... And I doubt it's a sensor issue, since it's all four gauges that don't work.
Is it very likely that my printed circuit board is bad? I was thinking that a new circuit board or gauge cluster set is the next step, but they're not cheap, and there's so many different types... So I'd like to see if there are other tests I can run before going that route.
1976: TWO different headlamp switches. Before serial number C25,001 & from serial number C25,001. Which one did you order? Serial number is the last 6 digits of the VIN
1976/78: TWO different printed circuit boards: With Oil/Amp GAUGES or with Oil/Amp WARNING LAMPS. Both are obsolete, but can be found NOS
Switch: I have ...C029XX as a serial #, so I'm assuming I need the older switch? I believe that's the one I ordered.
PCB: I have the one with oil / amp gauges. I've found them on eBay, but usually upwards of $200+ for my specific model. Would hate to buy a new one if I just have a loose wire somewhere...
Pretty sure my cluster back is the dust-crumbling type, the original model.
Easy test for the gauges. Pull the wire off the water temp sending unit, use a jumper wire to connect the wire to the sender to a good ground. Turn the key on. If the gauge, wiring from the gauge, IVR, & power to the IVR is good, the needle will rise. Try the same thing with the oil sender & fuel sender. The easiest thing to replace to start is the senders, then you need to pull the cluster & see if you are getting voltage to the plug location # 14. It is a black wire that supplies power to the IVR. If you have power to 14 with the key on, your IVR could be bad.
Amp gauges work on very low voltage, powered by a shunt, & seldom work, so don't worry about that one.
With the cluster out, you can test each gauge. 1.5 V battery, two jumper wires. Run a wire to each stud on the gauge, other ends to the 1.5V battery. Gauge should rise. If it doesn't reverse the leads on the battery & try again. If it doesn't rise, gauge is bad. I've rehabbed 15 or so of these clusters in the past year. I've come a cross a couple of bad gauges, 1 bad IVR. A few bad printed circuits, those are easy to spot as they are visibly cooked. Sometimes the PC needs to be cleaned where the gauge bolts to the cluster.
One thing I have found is that it doesn't pay to try & fix things one at a time. Rather, it is better to completely disassemble the cluster, clean everything, test every last component down to the bulbs & holders, then reassemble. Then you will have a cluster that will work.
I have an old plug off the harness I use to power each circuit on the cluster for test purposes. Makes things a lot easier.
There's a ground for the instrument panel which is screwed to the Y brace which supports the steering column. Check to make sure that it is there and connected to a good ground.
If your cluster back is crumbling, then the harness connector might not be making some or all of the circuit connections, if the crumbling is close enough.
Switch: I have ...C029XX as a serial #, so I'm assuming I need the older switch? I believe that's the one I ordered.
PCB: I have the one with oil / amp gauges. I've found them on eBay, but usually upwards of $200+ for my specific model. Would hate to buy a new one if I just have a loose wire somewhere...
I had already replaced the IVR, but it didn't make a difference. I tried to jump the oil sending unit wire to a ground, and it didn't respond. So I pulled out a battery and connected to the gauges, and got no response. I'm guessing my gauges are bad then? I tested them from the screw posts sticking out the back of the cluster.
I'm definitely getting some power to the cluster, since I get my blinker lights (at times) and my fasten belt light (at times).
The PCB looked okay from visual inspection, but I'm not sure if there's a better way to test it.
If you used a 1.5V battery to put power to the gauges, & you reversed polarity on them, & the studs are clean, & each individual gauge did not work, the gauge is bad. Out of 100 gauges, I would guess I come across 3 or 4 that are bad. I would be surprised if all of your gauges are bad, but maybe they are. The needle will not jump up instantly when it gets power, it takes a few seconds for the needle to start to move, & it moves slowly. 1.5V is enough to get about 1/4 of the way up the scale, 3V will go 3/4 or more up the scale.
Did you replace the IVR with new or used? These day new doesn't always mean good. Do you have another one to try? Did you clean the contact areas well on the PC where the IVR attaches??
Most of the individual functions on the cluster get power from separate sources, but share the ground path. So, if you have some lights that work, your ground is good.
If you end up needing gauges, I probably have some extras around the garage. They would be tested good.
Ah, no I just assumed it would peg quickly. I went back and tested again with the battery last night, and after a moment of holding power to the studs I was able to get the gauges to move. So I guess the gauges are working. When you ground the sending wire off the sensor, does this one also take a moment to begin to move? I may want to try that test again as well.
I replaced the IVR with a new one. I don't have another one to try, but the connections all looked very clean when I installed it. Can it be tested somehow?
The ground must be good then, as I have 2 or 3 lights that work. Do the blinker lights and the fasten belt light all go through the IVR as well? Or is it just for the movement of the gauges?
When you ground the sending wire it does take a little while for the needle to move. Just don't keep the wire grounded for too long as this method of testing pegs the gauge, rather than going part way up like the 1.5V battery test does.
You can put a volt meter between the sending unit wire & a good ground to see if the IVR is working. You'll see the voltage bounce around on a digital meter, usually from a couple of volts down to zero. Or use a test light the same way, it should blink on & off, that will let you know that the IVR is working. This is with the cluster plugged in to the harness & the key on. This test assumes that the IVR is getting power thru terminal 14 on the plug, & that the wiring to the sender is good.
The IVR is just for the oil, temp & fuel gauge. All the other lights get the power from different circuits.
Got the headlight switch replaced, which stopped the 2-3 working dash lights from flickering on and off. Also caused my dome light to start working again, as well as the seat belt buzzer.
I tested for voltage at the gas tank, since it has red and black cables. No voltage there, but the ground seems good.
Did some testing of the pigtail connector that plugs into the dash. When the key is off, I have power to 11 & 12. When the key is on, power to 1, 11, 12. When the key AND the headlight switch are on, power to 1, 7, 10, 11, 12. At NO POINT do I have power to pin 14; I assume this is why my gauges don't work, since they responded to the 1.5v battery test and there's no power going into the IVR.
So what's next? Where does pin 14 lead? Any other connections I can check that may be broken / unplugged along its route? Or is it easier to just tap into something and run a new wire to pin 14?
I also did a closer inspection of the PCB, and it appears to be in decent enough shape. I tested for continuity from the pin connections to various areas and it tested out fine. And the ground on the Y bracket behind the gauge cluster tested fine.
So what's next? Where does pin 14 lead? Any other connections I can check that may be broken / unplugged along its route? Or is it easier to just tap into something and run a new wire to pin 14?
I tested for voltage at the gas tank, since it has red and black cables. No voltage there, but the ground seems good.
Was the key in the RUN position when testing for voltage by the way?
Just checking. Would not be the first time working under the truck that I've forgotten to turn the key on!
If so though, and still no voltage reading on the power lead, then something is wrong between the gauge and the tank connector.
Gonna have to track that down. But you should be able to measure if there is voltage coming out of the gauge. Then find out if it's reaching the main instrument connector. If not, then the printed-circuit film is suspect I would imagine.
Originally Posted by MWB323
I assume this is why my gauges don't work, since they responded to the 1.5v battery test and there's no power going into the IVR.
No power to the IVR with the key in RUN is a dead giveaway that there's a break somewhere. If one of those pins is the input to the IVR and you don't see matching power reaching the IVR, then again, the circuit-board film is the most likely culprit. Unless there is a separate ground that's not connected?
Originally Posted by MWB323
I also did a closer inspection of the PCB, and it appears to be in decent enough shape. I tested for continuity from the pin connections to various areas and it tested out fine. And the ground on the Y bracket behind the gauge cluster tested fine.
Hmm. Don't know then. Wish I had a pinout of the connector, but all I have is a basic wiring diagram. With all the tech information that some of the members here have though, I'm sure someone will post up a flow chart with pie-graph and circles and arrows with a description on the back of each one!
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I believe that's the one I ordered.
for my specific model. Would hate to buy a new one if I just have a loose wire somewhere...
