I have a 1983 f250 with the 300 L6, my speedometer and fuel gage don't work. How can I go about fixing this?

 

Well the speedo is by cable from the transmission if 4x2 or transfer case if 4x4.
Dose the mileage part work or none of it?
Disconnect the cable from the trans end and look at the teeth on the gear of the cable and look into the trans at that gear.
Sometimes the plastic gears wear and the teeth dont mesh to spin the cable.

If they look good get a helper and a drill and fix it to the cable end and spin the cable. Note the speedo will only work in 1 direction.
Have the helper look at the gauge when spinning if it works than I would say it is the gears.
If it dose not spin pull the cable from the truck and pull the inner part out and see if it is broken.
Or you can just replace it. Measure yours and get a new one from the parts store or Rock Auto.
If the cable is good then it is the gauge that is bad and needs to be replaced.

On the fuel gauge you have dual tanks or single?
You have checked the fuse? Dont just look at it but pull it, clean the fuse ends and the holders and then check the fuse with a meter or just replace with new. I say dont look at it as they can go bad at the ends and cant be seen. Also they get some funk on the ends & holders and why to clean them.

If that dose not get it to work at the tanks sender, you should have 2 wires. 1 is a ground the other the gauge wire.
I like to use a test light with old school bulb not a LED bulb as it may give a faults test.
Key on test light hooked to ground check each wire and if the wire from the gauge to sender is good you should see the test light blink on 1 of the wires. The other should not blink as it is a ground now hook the test light to this ground wire and test the blinking wire again.
If you get blinking again the sender is bad.

The other way to test the gauge but is a little harder is with key off ground the sender wire (what one is it? and do you have a good ground & connection?) turn on key and if you have the right wire and good connections the needle should move.
DO NOT leave the key on too lone as it can hurt the gauge.

Now if you have dual tanks you need to do this test on each tank and if the light dose not blink or the gauge move with it at either tank you will need to test the switch. You will need to pull the dash to get at the switch.
With a test light and key on 1 of the wires going to the switch should have power all the time this powers the valve.
Another wire should blink and if you ground this wire the gauge should move.
If this moves the gauge then the switch is bad and needs to be replaced.

Now if you dont have any blinking with either type of fuel system do the temp and oil gauges work if you have them?
If they do not work then the IVR on the gauge cluster is bad and needs to be replaced.
Or the printed board could be bad I would replace both (IVR & printed board) if I had the cluster out this far.

Hope it is just a bad sender but that can be work to replace it also.
Good luck
Dave ----

 

90% of the time the fuel gauge problem is the sender. I have seen the dash switch go bad also, but not as often as the sender.

 

In addition to Dave's great advice, I want to emphasize you've got two separate issues. The speedometer is mechanically driven by a cable. The fuel gauge is electrically operated. The only thing in common is they are both located in the instrument panel.

If you need to remove the instrument panel, you'll need to disconnect the speedometer cable. If you've never disconnected a Ford speedometer cable before, check out this video. It's from a car of that era, not a truck, the principle is the same:



For troubleshooting the fuel gauge, some more details will help. Single or dual tanks? Does your truck have idiot lights or gauges for the oil pressure and coolant temperature? If gauges, do those two work normally?

 

The truck has dual tanks and the pressure and temperature guages work just fine.

 

Good to know the other gauges work correctly. That helps rule out a lot of things.

Here's a wiring diagram for 1981, I think it should be close for 1983. The second page has some troubleshooting info:

https://www.garysgaragemahal.com/fue...r--gauges.html

The fuel level, oil pressure, and coolant temp gauges are all the same internally. The only difference is the label on the front. 10 ohms = High, 73 ohms = Low.

With dual tanks, you're not likely to have two bad senders. Not impossible, but not high on the list. If you remove the tank selector switch, you can easily read the resistance to ground through the two senders. You can also check for continuity through the switch in both positions. Last but not least, you can momentarily touch the wire from the gauge to ground. 10 ohms would drive the needle to High, so it will go slightly above that with a direct connection of 0 ohms. This will tell you if the gauge itself is working.

 

Ok thank you. Looks like I have some testing to do.

 

Don't be surprised if both sending units are bad. They are prone to failure in these years. One goes out and the previous owner doesn't fix it, and then the other one goes out during or shortly after he sells it.

 

Yeah, and he should probably just rip out the factory system and install a mechanical fuel gauge. The factory gauge just says E and F at the ends of the band. Can't trust that. We need numbers!

 

Yes, quite common for both senders to be bad or perhaps way off after 30+ years.