69 MF 135 Diesel gauges not working

Glassdoc

New User
My oil pressure gauge works and the tachometer works but nothing on the fuel, ammeter, or water temp. Also, the headlights don't work. Ive tried bypassing the oil pressure switch and still nothing. My next theory is that it has to do with only the white wire hooked to the alternator. Gray and blue are not hooked up. Any suggestions or tests I can perform?
 
I have a wiring diagram for 135 Diesel that shows a Delco alternator with external regulator. Blue and gray wires connect between alternator and regulator, so if they are not hooked up the alternator will not charge. White wire connects alternator output to the ammeter.

My diagram appears to show oil pressure, water temp, and tachometer being mechanical, not electrical gauges. Thus, other than background light, these gauges would be unaffected by electrical problems.

Fuel gauge shows to be powered from the alternator external regulator, so non charging alternator may be affecting powering the gauge. There could also be a wiring, gauge or sender problem.

Head light failure could be a wiring, fuse, switch, socket, bulb or ground problem.

With regulator disconnected and no alternator output, ammeter will not swing to + showing charge and being a diesel with no distributor current draw, and no lights, there will be little ? discharge shown.

The 135 enjoyed several years of production run, so there may well have been other configurations used besides the diagram I have.
 
I was puzzled by the one wire hookup to the alternator when I bought the tractor several years ago, but it has always started. I've never changed the battery or charged it.

Just so I understand, are you saying the alternator is not charging my battery? Or is it charging but not providing power to the regulator and in turn not providing power to the fuel gauge and headlights?

Are there any tests I can perform to get to the bottom of this or do I need to hook up the blue wire and gray wire to the alternator before moving forward? Gray wire to the F/R terminal and blue wire to the same terminal as the white?
 
Leave the alternator alone. Sounds like someone has replaced original alternator with a Delco 1 wire internal regulated. Apparently it is charging since your battery is not giving problems. That is good. Leave gray and blue wires disconnected. If it is a 1 wire Delco you do not use the old regulator, but it may have been left on to serve as connecting points for the conversion.

Take a volt meter or test light and see if you have power at the fuel gauge. My diagram shows a key switch to supply 12 volts to alternator regulator. Output of this switch could now go to fuel gauge

Do you have mechanical or electric gauges for oil and temp?

For lights, use volt meter or test light and check for power at fuse, switch, switch output, light sockets, bulbs and insure a good ground at all housings. Rusty mounts do not make good ground.

Where does the white wire from alternator output go? It should go to one side of ammeter and a wire from other side of ammeter to battery connection at starter solenoid. Light and key switch should power from alternator side of ammeter.

Not knowing if diagram I have matches the way your tractor is wired, I know this is generic information, but hopefully can give you a starting point.
 
The water temp gauge needs replacing since it is mechanical, and far as the other gauges, lights not working if it were me I would replace all the gauges except for the tachometer, replace the switches, light bulbs, and re-wire it. Wiring on these old tractor can turn into a real rats nest over with all kinds of quick improper repair, just old, and neglected.
 
I will test for power at the fuel gauge. But regarding the key switch, it is a diesel so the key switch only has "start" position and "off" position. It springs back to "off" after you start it. It has a pull kill switch. This model has an oil pressure switch that switches power to fuel gauge etc. when the oil pressure is past a certain limit. But I bypassed that switch and tested fuel gauge and lights and still nothing.

Oil and temp gauges are mechanical.

White wire from alternator does go to the ammeter. And other side of ammeter goes to oil pressure switch. The ammeter stays on zero. Maybe it's working, maybe it's not.

I had assumed the oil pressure switch could be the problem for both of these but I'm not sure if the oil pressure switch controls power to the lights or not.

And it does seem as though the water temp gauge needs to be replaced.
 
If someone could take a photo of the plug that
plugs into the light switch so I can identify which
wires are attached to the terminals that would be
helpful. Or if there is a diagram available. I can't
seem to find one.
 
The I&T manual has a wiring diagram that shows all the connectors. Is there something in specific you are looking for? On my 135 gasser i am only using pins 2 and 5 for lighting. 5 is the battery connection and 2 is the first setting when you turn the knob on. I have 2 powering both dash lights and headlights.
 
I suppose I could have done that. :oops: Well now that I've ordered a new switch I suppose I should hook it all up correctly. If you have a diagram labeling the posts on the back of the switch and the color of wire that attaches to each.
 
I've got two items I'm trying to fix here and I hope the new switch and wiring diagram will be the end of the light problem. Next problem is the fuel gauge. I've read so many posts about people buying a new gauge or sender and after installing finding out that wasn't the problem at all. So I want to make sure I test this thing thoroughly before buying new parts. I've got 12V with a test light to every place that should have it for the fuel gauge but I need to get my voltmeter out to test the sender. What kind of volts should I be getting from the sender? This is a diesel with one wire to the sender and a grounded "tab" that grounds from the sender plate to the tank.
 
If you look at the fine print on the bottom of your gauge it might say what ohm range it should have. You measure resistance and not voltage for the sending unit itself. For example mine is 240-30 ohm range. A good ground is required for that sending unit too. If it's not working right try running a dedicated ground wire from that tab on top of the sender under a screw and see if anything changes. I'll try to scan in that diagram in the morning and post it if someone else doesn't beat me to it.
 
Hopefully this is readable..
4290.jpg
 
I got the lights fixed. Woo hoo! It was a
combination of new switch, new connector and
cleaning the grounds.

My other problem is the fuel gauge. I've checked
the ground with a multimeter. It is getting a good
ground. The fuel gauge has two wires. One to the
gauge, the other to the regulator. When I hook the
multimeter to the wire going to the regulator I get 0
ohms and -4.3ish mV. This is a diesel tractor with an
oil pressure switch. I get 14V to the regulator from
the oil pressure switch when the tractor is running. It has been converted to
12V so the regulator is just a connection point. Not
sure, but I don't think I can run 12V to the fuel
gauge so it has to go through the regulator, right?
Do I need a new regulator, a new fuel sender, or is
there some other test I can run?
 
You want to run switched 12v power to the B terminal of the gauge. The oil pressure switch is most likely the switched power source in this case. The T terminal is the line that runs to the tank sending unit center post. If you hook your meter to the center post of the sending unit and the other lead to ground you should get an ohm reading of either 30 or 240, approximately, from the sender when the bobber is down all the way (empty tank). If you raise the bobber the ohm reading should change either up or down depending on which setup yours has. If you get a reading between 30-240'ish with a full range of motion (empty to full positions) on the bobber then the sending unit is good. If it doesn't then either the ground for the sending unit is open or the unit is bad.
 
So the power from the oil pressure switch can go
straight to the gauge instead of through the
regulator?
 
So I hooked 12V from the oil pressure switch to the
gauge. I when oil pressure switch kicks in gauge
goes to full. I checked the ohms on the sender, it
was about 50 full and 190 empty. Gauge says 30-
240. I'm thinking it is the connection from the
regulator. I know it regulates voltage but that's really
all I know.
 
Connection from the regulator should just be source voltage. Has the gauge ever worked correctly? 50-190 ohms should put the needs a little above empty and a little below full.
4483.jpg
 
I've had the tractor a couple of years and it's never
worked. When I hooked the 12V direct instead of
through the regulator it did "work" in the fact that it
moved to full when the engine was running. The
tank was almost empty. I feel like the sender is
working. It seems that I've narrowed it down to the
gauge? Is there a way to test it?
 
Not that i can think of easily... Basically put the sender and the gauge on the bench wired up and work the sender and see if the gauge moves. About it..
 

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