Fuel guage and amp guage on MF245

Hello,
Been running down electric problems on MF245 D
New + cable, checked all wiring, new battery, new Oil Pressure Switch, added a disconnect on the - side.
All seemed to be ok until today.
Noticed Amp gauge not reading and fuel gauge jumping back and forth and mostly staying on the E side.
Checked alternator and it's not charging. Under warranty. Will replace.
I'm hoping the Amp gauge goes back to working but why is the fuel gauge acting up now?
Would the alternator problem cause this also?

I've got a MF 235 gas. Seems I had trouble
with the key switch years ago. Tractor done
some funky things when that went bad.
Factory switch was either hard to find, or
couldn't get it amymore (don't remember
which). Put an aftermarket jobby on it.
That lasted for awhile (not to long), and
it went bad. Got tired of playing with the
head ache, and ran a jumper wire to the
coil, and use a battery charger to charge
the battery back up. Use a screw driver at
the starter to start it.

Not saying your key switch is bad, but
might be a good idea to check things out
there, just so you know there isn't an
issue there. I know you don't have a
distributor/coil with a diesel, but that
switch pretty much turns all else on and
off.

How long did it work correctly after you did the electrical replacements you listed? Is your wiring done the same as the Operator's manual shows? If so, the key switch only operates the starter. The oil pressure switch controls the fuel gauge (also the temp gauge if that gauge is electric on your 245 diesel) and the excitation wire (with a diode in it) to the alternator. Have you checked that there is power through the oil pressure switch when the engine is running? Is the alternator still a three wire as original? Is there power to the excitation terminal (#1) on the alternator when the engine is running?

How long did it work correctly after you did the electrical replacements you listed? Is your wiring done the same as the Operator's manual
shows? If so, the key switch only operates the starter. The oil pressure switch controls the fuel gauge (also the temp gauge if that gauge
is electric on your 245 diesel) and the excitation wire (with a diode in it) to the alternator. Have you checked that there is power
through the oil pressure switch when the engine is running? Is the alternator still a three wire as original? Is there power to the
excitation terminal (#1) on the alternator when the engine is running?

It was working correctly for about three days until the alternator went out.
Prior to that I did replace the oil pressure switch.
Replaced the alternator yesterday and the Amp is working now but the fuel gauge is still acting up.
I have traced all wiring according to the schematics.
It is a 3 wire but I have been told that I do not need the diode in the #1 wire anymore.
Before I replaced the alternator there was power to the #1 with engine running. Did not check after replacement.
The new alternator is showing good voltage.
How do I check to see if there is power through the oil pressure switch when the engine is running?

The switch seems to be working ok.
I know things don't always seem to be what they are.
I will check it out.

Try adding a ground wire from one of the fuel sender screws to a chassis ground. Sometimes the ground path fails. It is possible there is a problem with the sender or gauge, unrelated to the alternator.

With the engine not running, only one terminal of the oil pressure switch should have power since the switch should be open without oil pressure. With the engine running both terminals should have power, if the switch is closing when it receives oil pressure.

Thank you,

I did the test you said. The OPS worked just like you said.
Before I add a ground from the fuel I took a test and here are the results.
Fuel gauge with tractor running, on the terminal on the full side I get 9.76 volts.
That is the terminal with a single black wire going to the top of the fuel tank.
On the terminal side toward empty I get 0.01 volts.
With the engine shut off it does not matter which terminal I test I get 12.98 volts.
What I find strange is when the tractor is running and setting still the gauge appears to be reading correctly.
When I put it in gear and start moving the fuel gauge starts to go crazy.

Tractor tanks and gauges are not as refined as auto ones, so I have seen some act like that and some that are slower to swing as fuel sloshes around in the tank. The sender likely has some wear and is looser in the joints and pivot than when it was new, which could be part of the issue. You need to check the sender with an ohmmeter to know what it is really doing. And it is easiest to do that with it out of the tank. Simple description of what is inside the tank: The float arm moves a contact across a resistor coil, so the resistance between the gauge and ground changes as the arm moves from empty to full which makes the gauge arm move. A new sending unit [u:2dc9cd9daf]might[/u:2dc9cd9daf] be steadier. Gauges and senders must match the ohm ranges so, if you decide to get one you need to get the right one for your tractor or it will not register correctly.

This post was edited by Jim.ME on 11/02/2023 at 04:08 pm.