275 any reason not to convert to a ignition switch with ACC?

[petebert]

Any reason not to ditch the diode system and just put everything onto a keyed switch with 3 or 4 posts?

275, have had it for about a year now. The gauges have never done anything and there's a mess under the dash from previous owners. I currently have other stuff taken apart and would like to tackle the gauges. Although with the original electrical setup you can't test anything without the engine running. Got me thinking, why even bother with this system that uses a diode wire to active everything? Why not put everything onto a 3 way key?

 

[Jim.ME]

Any reason not to ditch the diode system and just put everything onto a keyed switch with 3 or 4 posts?

275, have had it for about a year now. The gauges have never done anything and there's a mess under the dash from previous owners. I currently have other stuff taken apart and would like to tackle the gauges. Although with the original electrical setup you can't test anything without the engine running. Got me thinking, why even bother with this system that uses a diode wire to active everything? Why not put everything onto a 3 way key?

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Diesel engine, correct? I don't see that changing to a keyed switch is going to reduce the mess any more than just straightening out what is there will do. Do you have the wiring diagram (usually in the Operator's Manual for Massey Fergusons) for it? I ask as the diode in my 255 and 1105 diesels is only for the alternator excitation. It does not activate anything else. Take a picture of your wiring diagram and post it, so we can all see the same thing.

You can test without the engine running. You make a short jumper wire with a male space terminal on both ends and use it to connect the two wires that are on the oil pressure switch, for testing purposes. The gauges are activated by the oil pressure switch, located in the tee at the back of the oil pressure gauge. Be sure to test the oil pressure switch itself. It should be open (not continuity between the terminals of the switch) when the engine is off and closed (continuity between the terminals of the switch) when the engine is running. Looks like you have an oil leak around the back of the oil pressure gauge. That is a mechanical gauge, if it is not working you either have a supply line issue or you need a new gauge. Does your ammeter work? That is not controlled by the oil pressure switch.

 

[petebert]

The oil pressure gauge actually does work, what are you typically replacing when it leaks? Is it usually the gauge or a fitting? And yes diesel.

The ammeter used to work but I haven't seen it move lately. The fuel and water temp gauges have never moved. I just measured the resistance at the back of the fuel gauge and it showed 100, so it does appear that the fuel sender is sending a signal. It appears they have the alternator wire to self excite?

Here's the wiring diagram and after making the original post I thought I'd start tracing the original wiring system and start by putting it back to original

 

[Harry in Ky]

Just personal opinion here, but I've always thought the Massey concept of using the oil pressure switch was good idea. It limits the damage caused by operator not getting the key switch in just the right place when shutting the engine off. Many switches have multiple positions but only one "off".

 

[Jim.ME]

The oil pressure gauge actually does work, what are you typically replacing when it leaks? Is it usually the gauge or a fitting? And yes diesel.

The ammeter used to work but I haven't seen it move lately. The fuel and water temp gauges have never moved. I just measured the resistance at the back of the fuel gauge and it showed 100, so it does appear that the fuel sender is sending a signal. It appears they have the alternator wire to self excite?

Here's the wiring diagram and after making the original post I thought I'd start tracing the original wiring system and start by putting it back to original

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The oil pressure switch turns on power to the wire having the diode in it to excite the alternator. At the same time, it turns on power to the gauges, the diode has nothing to do with the gauges getting power.

The oil leak could be the gauge, loose fitting or a bad fitting. You need to clean the area up with some brake cleaner, or such, and find the leak.

 

[petebert]

After going out and messing with more I think I'll try going original instead. They've got the wiring going all sorts of different directions that don't match the diagram. I believe it's the pressure switch that's leaking so I'll replace that. And when I put twelve volts to the fuel gauge it moved, water temp didn't move but it's probably too cold out for that

 

[petebert]

The oil pressure switch turns on power to the wire having the diode in it to excite the alternator. At the same time, it turns on power to the gauges, the diode has nothing to do with the gauges getting power.

The oil leak could be the gauge, loose fitting or a bad fitting. You need to clean the area up with some brake cleaner, or such, and find the leak.

Going over everything I need to redo everything per the wiring diagram. Any recommendations on what to use for the diode? It's still available through agco, although you might have to order a 25 pack. I tried googling 10 ohm diode but don't know enough about them to know if it's the correct one

 

[Jim.ME]

Here are a couple diode numbers that will work. 1N4007 is 1 amp, 1000 volt and a 1N5408 is 3 amp, 1000 volt. You can get them on eBay in smaller quantities than 25.

The diode (or indicator light, or 10 ohm resistor) is to prevent feedback of power to an ignition system on a gas engine or the electric powered fuel solenoid on a diesel, which would prevent the engine from shutting down when the key is turned off. Your tractor has a pull cable for the fuel to shut the engine down, doesn't it? Using the oil pressure switch to excite the alternator will work just fine without a diode in that wire. When you pull the stop cable, the engine stops, stopping the alternator. It can only feed power back out the excitation terminal (#1 spade) when it is running and producing power, so it will not put power to the gauges when the engine is stopped.

 

[petebert]

Here are a couple diode numbers that will work. 1N4007 is 1 amp, 1000 volt and a 1N5408 is 3 amp, 1000 volt. You can get them on eBay in smaller quantities than 25.

The diode (or indicator light, or 10 ohm resistor) is to prevent feedback of power to an ignition system on a gas engine or the electric powered fuel solenoid on a diesel, which would prevent the engine from shutting down when the key is turned off. Your tractor has a pull cable for the fuel to shut the engine down, doesn't it? Using the oil pressure switch to excite the alternator will work just fine without a diode in that wire. When you pull the stop cable, the engine stops, stopping the alternator. It can only feed power back out the excitation terminal (#1 spade) when it is running and producing power, so it will not put power to the gauges when the engine is stopped.

Yes, fuel cable shutoff and no "on" position for the key, it just has a springed start position. Just going on fuzzy memory, I thought I read the diode prevents a parasitic drain or something? But yeah if I don't need it, I don't have a problem with skipping it.

 

[Jim.ME]

Yes, fuel cable shutoff and no "on" position for the key, it just has a springed start position. Just going on fuzzy memory, I thought I read the diode prevents a parasitic drain or something? But yeah if I don't need it, I don't have a problem with skipping it.

It won't hurt to have it there, but I don't believe drain will be an issue. Several choices on eBay for less than $5.