Glow plug wire has power when disconnected, no power when connected to glow plug buss bar.

[EVVFarms]

I have too many tractors to not be a member of this forum so I decided to join, hoping / praying for some help on a problem I can’t seem to solve on my own. Hopefully in the future I can contribute some too.

The glow plugs on my tractor are not working. The power feed wire to the glow plugs operates as it should when it is disconnected from the glow plug buss bar (glow plug light turns on, 12V power for 6 seconds when key is turned to run, and constant 12V power when turned to start) however when the power feed wire is hooked up to the glow plug buss bar I can turn the key to the run or start position and there is no power to the glow plugs.

Tractor Description:
Toro Z597-D Z Master
Model: 74269

Motor Description:
Daihatsu Motor Co., Ltd
Type: DM950D-C
Model: 582447 (Briggs & Stratton Vanguard Diesel Series)

Here are all of the things I have done to rule out various components:

• Freshly charged battery; 13.00 volts
• All safety switches have been tested
• All relays have been bench tested and function properly
• The relay plugs and getting power in all my tests
• The glow plug heat controller has been tested and is functioning properly
• All fuses have been checked
• Glow plugs have been tested while installed in the motor, all are good (0.7-1.0 ohms)

I feel like there is something simple I am missing, I just can’t figure it out. Any help would be GREATLY appreciated.

Thank you.

 

[bluecon1]

I'll take a wild stab in the dark. I would say that it could be a possible "bad connection". Connection is OK to test for power with glow plugs disconnected, but when the load is actually put on circuit, the connection is lose or corroded. I've experienced this on a circuit before. Good luck in solving this.

 

[EVVFarms]

I'll take a wild stab in the dark. I would say that it could be a possible "bad connection". Connection is OK to test for power with glow plugs disconnected, but when the load is actually put on circuit, the connection is lose or corroded. I've experienced this on a circuit before. Good luck in solving this.

Thank you. The connections all look good, it is a low hour machine, always stored inside, zero corrosion on anything. I will go out to the garage and recheck.

I am not sure when the problem started. The tractor wasn't charging and I dragged the battery down to nothing a couple times and needed to be jumped. I fixed the alternator, maybe the problem started after that. So I was thinking maybe the battery couldn't handle the draw, but if it can handle enough draw to turn the started with no issue, then it should be able to handle the draw from the glow plugs.

 

[MattB4]

Thank you. The connections all look good, it is a low hour machine, always stored inside, zero corrosion on anything. I will go out to the garage and recheck.

I am not sure when the problem started. The tractor wasn't charging and I dragged the battery down to nothing a couple times and needed to be jumped. I fixed the alternator, maybe the problem started after that. So I was thinking maybe the battery couldn't handle the draw, but if it can handle enough draw to turn the started with no issue, then it should be able to handle the draw from the glow plugs.

Double check your ground connections.

 

[Fuddyduddy1952]

As an electronic technician the fix is easy.
Just follow the red line. Ground meter --neg. black lead at battery-- negative. Meter red + positive at battery + positive. Let's say it's 12.7v. Now move meter up to f2 40A fuse, side going to battery. It should be 12.7v. Turn key on then off...should stay at 12.7 (or close). Move to other side of fuse...same key on-off test. Then move to relay...same key on-off. Just a couple seconds for voltage reading, you want glow plug light on not cycle off. Keep moving meter along towards glow plug buss. From what you say it will be zero volts. So it's either fuse (bad or corrosion), relay (contacts bad) or bad (open) wire.
Super simple.

 

[EVVFarms]

As an electronic technician the fix is easy.
Just follow the red line. Ground meter --neg. black lead at battery-- negative. Meter red + positive at battery + positive. Let's say it's 12.7v. Now move meter up to f2 40A fuse, side going to battery. It should be 12.7v. Turn key on then off...should stay at 12.7 (or close). Move to other side of fuse...same key on-off test. Then move to relay...same key on-off. Just a couple seconds for voltage reading, you want glow plug light on not cycle off. Keep moving meter along towards glow plug buss. From what you say it will be zero volts. So it's either fuse (bad or corrosion), relay (contacts bad) or bad (open) wire.
Super simple.View attachment 847750

I appreciate the hand holding! I am diving in now, it might take me a while, it is really tough to access everything. I will report back as I know more. Thanks again.

 

[George2615]

How did you test the glow plugs? Did you remove the buss bar connecting them together then check each plug individually? If the glow plug light works normal when buss bar is disconnected but not when hooked up it seems to me you have a plug that is shorted to ground.

 

[EVVFarms]

How did you test the glow plugs? Did you remove the buss bar connecting them together then check each plug individually? If the glow plug light works normal when buss bar is disconnected but not when hooked up it seems to me you have a plug that is shorted to ground.

I removed the buss bar and check each individually. I did not remove them from the block. I connected the negative probe of the multi-meter to the block side, then the positive probe to the top of the glow plug. All tested 0.7 to 1.0 ohms.

I am currently working on better access to the wiring harness to follow the @Fuddyduddy1952 procedure.

 

[Fuddyduddy1952]

How did you test the glow plugs? Did you remove the buss bar connecting them together then check each plug individually? If the glow plug light works normal when buss bar is disconnected but not when hooked up it seems to me you have a plug that is shorted to ground.

That would blow fuse.

 

[5030]

Thank you. The connections all look good, it is a low hour machine, always stored inside, zero corrosion on anything. I will go out to the garage and recheck.

I am not sure when the problem started. The tractor wasn't charging and I dragged the battery down to nothing a couple times and needed to be jumped. I fixed the alternator, maybe the problem started after that. So I was thinking maybe the battery couldn't handle the draw, but if it can handle enough draw to turn the started with no issue, then it should be able to handle the draw from the glow plugs.

Looking good and being good are 2 distinctly different animals. If I were you, I'd first remove the glo-plug buss bar and clean all the connections with an abrasive, clean and bright and re-install it then clean all the connections that are intrinsic to them as well. Sound to me like you have a corroded high resistance connection somewhere. One thing I've always done is first thing on a new unit, I pack all the Molex and conventional connectors with di-electric grease and coat all the exposed connectors (including the battery terminals with 'Fluid Film' I know, Fluid Film is supposed to be undercoating but it's also a very good corrosion inhibitor for exposed electrical connections as well. Been using it for years now and yes, I do use it for undercoating as well but I use the black Fluid Film for that.