Help with glo plugs! MT372

BTackett · Mar 30, 2008

I am in the process of semi-restoring a Mitsubishi MT372 ( as you probably have seen pics here ) and before removing the wiring harness the glow plugs were working fine. I installed a new ignition switch ( 5 prong w/preheat Kubota switch ) and it would turn over but not glow plug. So, I put the old switch back on that worked before ( reason I replaced was that it was sticking in the run position, preheat worked fine ) and now it turns over but no preheat. What could be wrong? I just removed one wire on the glow plug itself and removed the entire harness. Now preheat will not work.

Any ideas?

I checked my wiring diagram and it shows a 4 prong switch but it was wired 5 prong previously and worked fine.

How exactly do glow plugs work and how can you check them at the switch with meter?

What actually causes the dash indicator to glow when preheating?

thanks,
Bill

shags-72 · Mar 31, 2008

They are just like a wire with some resistance to cause them to heat up and help ignite the combustion charge. The indicator in the dash should be hooked up inline with the glow plugs off of the heat side of the ignition switch. It is kinda like another glow plug so it just heats up also. My wiring diagram shows a 5 prong switch with the g1 and g2 poles going to the glow plug indicator poles. Gi to the input side and G2 to the output side of the indicator. The rest hook up as shown on the back of the switch I.E. st black w/yellow wire, bat black w/ white wire, acc yellow wire. You can with a meter and it should be in ohms reading and 1-1.2 ohms. Now this is from my own mt372 owners manual and it differs from the maintenance manual on the site but I know this is a real manual and the right one because it is my hands and it is a real mitsubishi manual.You can also take them out and hook them up to a battery and see if they glow red within 25seconds. Also check the glow plug indicator in the dash it says that it is .9-1.1ohms or can check with a battery also. These are 10-10.5 volt plugs so don't leave them on the 12 volts for v much longer than the 25-30 seconds. This all came out of the service manual which I got for free in digital format from site which you will have to join to get access to the files.

http://groups.yahoo.com/group/Mitsubishi_Sato_Tractors/files/MT372 SHOP MANUAL/

Ps this site kept loggin me off so sorry if I double posted or anything like that.

shags-72 · Mar 31, 2008

I just looked at the pretty much finished pics. That thing is awesome! But did you make sure that the paint was off of the plugs? I couldn't tell from the pics. It is beautiful man.

What was the number on the fan belt? I just changed all the fluids and my belt was toast.

PILOON · Mar 31, 2008

A glow plug circuit is basically all plugs (and indicator) wired in parallel.
(in parallel if one burns the others still glow).

A simple test is to use an ohm meter from the glow plug terminal to ground.
Each plug will read LOW ohms if OK (shags says 1.2 ohms).
Remember to disconnect the lead before taking a reading otherwise you will be reading all the plugs as they are in parallel!

You can (if desired) simply use a momentary push switch that you depress for whatever time you want to get the plugs to glow.
With the indicator you can merely hold the the switch depressed until it glows which therefore indicates the plugs are glowing as well.

When real cold (like -25c I need to hold mine for + 1 minit)

If one was to use this push button approach, one needs to find a high amp switch as a mere 'doorbell switch' would simply melt, that or use a relay.

Frankly at the prices wanted for origional type switches I'd opt for the manual approach for the glow plug activation as one would only need a simple 'on off' key switch (from any auto part) for all the other functions.

I ran a 6.2 GMC for almost 8 years with a push switch mod primarily due to the fact that GM wanted about $150. for their relay.
Never burned a glow plug (and GM has no indicator either). I'd simply time the application, eg 1000, 1001, 1002 etc for about 6 seconds (GM used FAST plugs vs MIT are slow plugs.
If 6 secs was inadaquate I'd re time to ,say, 8 or 10 secs on the next start attempt.

Stewmeat · Apr 1, 2008

Hello, I have an older MT372D too. My glow plugs didn't work and I figured that the little cup with the heater indictor for the dash was my problem. That little wire burned out. Napa has them or you can just by-pass it with a jumper wire... 10 seconds of heat and mine normally starts fine.

Good luck!

BTackett · Apr 1, 2008

Thanks for the info. I checked last night and I only have about 3.2v on the battery wire on the switch. Hhmm. The bat wire goes straight to the solenoid on the starter and then jumps off to the alternator output right? I checked the inline fuse and I do not have 12v either.

I then did a continuety(sp??) check from the bat wire on the back of the switch to the hookup on the soleniod and it is contant so there is no breaks in the wire. Geez, this thing is driving me crazy.

The voltage regulator should not have any affect on static current should it? Only when the alt is running and putting the 12+ volts into the system?

If I make a jumper from battery to the back of the switch the glo plugs should then work on the preheat right? I have not done that yet but it looks like that is next. I also do not have 12v to the headlights and ran a seperate wire through a 15amp fuse the new headlight switch to get them working. I hate messing with old wiring harnesses. I should just make a new one.

The glow indicator is in good shape and not burned up. It worked before removing the harness.

Shags, I have the belt number at home. It is the same belt used on a 88 buick skylark #15340 I think. I will look tonight and PM you.

Bill

BTackett · Apr 1, 2008

Shags, I sent you a PM. But for anyone else the belt is a Dayco 15340.

thanks.
Bill

Eagleview · Apr 4, 2008

Run a temporary jump wire straight from a known 12volt source to the supply pin on the switch and see if that works .

BTackett · Apr 4, 2008

It has a wire jumper from glow plug to glow plug and it is not grounded. I jumped a 12v wire from battery directly to input side of the glow indicator and it did nothing.

I am lost now.

BTackett · Apr 4, 2008

Here is a picture of the glow plugs. I also ran a jumper from the battery to the Bat post on the switch and nothing.

Eagleview · Apr 4, 2008

Try putting the 12volt supply on the output side of the indicator . If that does'nt work put the 12volt supply directly to the 1st glo plug . If that works it's in between the two . It does'nt have a glo plug controler does it ?

shags-72 · Apr 5, 2008

I know that battery looks new but is it good at least 12.5 volts? Measure it at the battery and then measure it at the poles on the switch. Have you pulled the glow plugs out and actually looked at them while you did the jumper thing from the battery? Don't forget to ground them while you do this and clean the terminals good. Did you measure the resistance on the glow plugs? If it shows no resistance then it is bad. Same with the indicator.

wushaw · Apr 5, 2008

Bill,
A glow plug is just like a spark plug it is a simple resistor. Ohm it out or pull one or both and put 12v to the top and ground the base and see if it heats up.

BTackett · Apr 5, 2008

I removed the glow plugs and put 12v from the battery directly on the top post while grounding it on the treads and the glow plug heated/smoked so I assume it was working.

I put my old swith back on and now I have 12v on the bat terminal of the switch but the glow indicator wire will not heat up. It did one time somehow so I put the switch back in the dash and the indicator back in the dash and tried it again and nothing. Even if I take 12v directly to the indicator it will not heat up but the jumper wire I used to one side of the indicator post got really hot! but the indicator still did not glow. Do you have to have 12v on both sides of the indicator for it to work?

This is really bothering me know and I am about ready to remove the entire preheat wires from the switch and wire a pushbutton switch or something for preheat. If only I could get the indicator wire to heat constantly.

Battery is 12.5 volts and I have not checked the resistance on the glow plugs as the first one in line worked when hooked directly up.

Also, If I leave the battery hooked up like normal and come back out the next day the battery is dead like it has a current draw.

Still lost.

Bill

wushaw · Apr 6, 2008

Sounds like your glow plugs are good. Check to see if the indicator wire is broken. That indicator wire is a resistor also, just like a light bulb.
You have a battery drain and need to find that, re-check your wiring.
Try this take a 12v test light or just any way to make a 12v bulb light and pull your positive lead on the battery and put the light in series with the battery and the pos battery cable and see if it lights up, if so you really do have a drain.

With the light glowing start pulling wires off your key switch to see which circuit the draw is on. This shouldn't take long since there ain't much to the 372.

shags-72 · Apr 6, 2008

Good idea Wushaw! I allmost forgot about the light idea. And you are right there isn't much to the 372 wiring. Does this thing have all the lights including the runners on the fenders?

BTackett · Apr 7, 2008

The glow wire indicator is in good shape. If I take a jumper directly from the battery to the input side of the indicator that jumper wire gets HOT! but the indicator does not glow. Maybe my battery is no good even though it is new. I will do the current draw thing and let you know what I find. I do have a current draw somewhere. I am also going to try another battery.

I have to remove the fuel tank as there is a leak somewhere in the seam on the bottom causing a slight dripping that I did not notice before .

Bill

wushaw · Apr 7, 2008

I have never seen my glow wire turn red even after 10sec on. CHeck the electrolite level in your battery after you charge it overnight on a trickle charger.
The little test guages are cheap, easy to operate and available at any auto parts store.

You may have to take your tank to a radiator shop to get a good fix on it. It probably sat with water in it for many years.

There is not a whole lot in the system that can cause a drain on the your 372 since it only has headlights, alternator/regulator, glow plugs and the three indicator lights for oil, charge and over temp.
If the headlights were on they would be lit and the same goes for the indicator lights so that leaves the alternator/regulator. You still need to trace it out to which circuit it is on though.

Shags-72, he doesn't have tail light lights so it's even easier to trace down.

Eagleview · Apr 8, 2008

BTackett said:
The glow wire indicator is in good shape. If I take a jumper directly from the battery to the input side of the indicator that jumper wire gets HOT! but the indicator does not glow. Maybe my battery is no good even though it is new. I will do the current draw thing and let you know what I find. I do have a current draw somewhere. I am also going to try another battery.

I have to remove the fuel tank as there is a leak somewhere in the seam on the bottom causing a slight dripping that I did not notice before .

Bill

You will find your jumper wire is rated a lot less than the tractor supply wire and certainly less than the indicator that's why it's getting hot .

BTackett · Apr 9, 2008

Thanks for everyone's reply. I have been really busy around the house and buying / selling trucks. I will try to get to this in the next week or so and let everyone know what I found. Almanac said to plant this coming weekend and we are going to try and get the garden out.

Bill