12 volts between the positive terminal of battery and glow plugs at all times, bad?

[SilverLakeFab]

I have a 1978 Kubota B6100 and I seem to have 12+ volts between the positive terminal of the battery and the electrical connection of the glow plugs at all times. Is that a bad thing? I'm trying to sort our why I can't get my machine to start. The glow plugs are brand new, the fuel lines are freshly bled, the engine turns over quickly, and I even have the block heater on so the motor is warm. Does anyone out there have any ideas for me to try? Also, am I correct that there should not be voltage between the battery and glow plugs when the key isn't even in the machine? If all signs point to poor compression, does anyone know where I can find a compression tester that will work on my little orange tractor? Any help is much appreciated!

 

[SilverLakeFab]

Would you folks agree that the ignition switch has probably gone bad if I have constant voltage between the glow plugs and positive battery terminal?

 

[plykins]

Seems to me you are just measuring voltage from the battery through the glow plugs to ground. Unplug one of the glow plugs and measure from that wire to ground when the glow plugs are activated. If no voltage they are not working.

 

[Buckgnarly]

Seems to me you are just measuring voltage from the battery through the glow plugs to ground. Unplug one of the glow plugs and measure from that wire to ground when the glow plugs are activated. If no voltage they are not working.

Agreed. All you are doing is using the glow plug as a ground. You need to check from glow plug back to battery or chassis ground to see if you are getting voltage to the glowplugs.

 

[SilverLakeFab]

If the switch is good, why would the glow plugs be receiving power when the key is out?
It seems to me that the glow plugs should only be receiving voltage when the ignition switch is in the glow plugs' on position. Does that not make sense?

 

[jimmysisson]

See if you have voltage at the glow plugs: ground the test light alligator clip and place the probe on the glow plugs. That will tell you if there's power there. The way you describe testing only tells you if the glow plugs can act as a ground. Report back.
Jim

 

[Willl]

Touch one end of your test lead to tractor frame, engine block or battery GROUND.

Touch other lead end to very tip of glow plug.

Do you still see voltage ?

 

[Soundguy]

If the switch is good, why would the glow plugs be receiving power when the key is out?
It seems to me that the glow plugs should only be receiving voltage when the ignition switch is in the glow plugs' on position. Does that not make sense?

you said you measured 12v+ from POSITIVE POST of the battery and the connection onthe glow plug.

that's not the same as measuring the switch.

take a step back and think about it.

draw it out on paper if you have to.

that glow plug is just a heater filament. in a n open circuit ( prior) to the plug.. that plug is gonna look like a ground reference to a test lamp or continuity meter. it's a very low ohm heating element.

 

[SilverLakeFab]

I apologize for not having much experience trouble shooting electrical items, so everyone's help is appreciated. I'm a mechanical engineer/fabricator/web designer, and I can wire a house with ease, but 12V stuff confuses me.

I just connected my multimeter to the positive battery terminal and positive connection on the glow plug and my meter read -13.49V (see picture at address below).

http://img.photobucket.com/albums/v347/kawiracer/Tractorvoltagereading_zpsce2ff547.jpg

When I place my negative lead on the negative terminal of the battery and the positive terminal on the positive connection for the glow plug, I get no voltage until I turn the key to the "heat glow plugs" position, and then I get a reading of only 10.96 to 11 volts. Perhapps that isn't enough to warm the plugs? Would that make more sense? I know that the engine is a little tired (about 1100 hours), but I'm hoping I'm not fighting an engine with low compression.

Thanks everyone!

 

[brain55]

That's about what I would expect with the voltage drop from the glow plug load. When you are cranking the engine over are you getting any smoke out of the exhaust? If there is no smoke then you have a fuel problem. If you are getting white/bluish smoke then you have a compression or preheating problem. You saying the engine cranks over fast makes me wonder about compression. I would check to make sure the decompression lever on the valve cover is returning properly too.

Brian