B7100D-Glow Plug Indicator

[mik1315]

My glow plug indicator does not glow but tractor does start.

My tractor is an early 1970 model (3,000 hours), gear driven not hydraulic. I checked the amp current in the wires to the glow plugs. Wire from starting switch to first cylinder/glow plug next to bulkhead/firewall read 17.8 amps, wire to middle cylinder/glow plug 11.1 amps, third wire to last cylinder/glow plug next to radiator 5.7 amps.

Is the current drop through the wires normal? Any suggestions?

I will clean the wire connectors and see if that helps.

Thanks,

Mike from Cleveland.

 

[torch]

I checked the amp current in the wires to the glow plugs. Wire from starting switch to first cylinder/glow plug next to bulkhead/firewall read 17.8 amps, wire to middle cylinder/glow plug 11.1 amps, third wire to last cylinder/glow plug next to radiator 5.7 amps.

The glow plugs are wired in parallel, but the wire feeding them is strung from one to the next to the next. So when you meter from the starting switch to the first cylinder, you are reading the current draw of all 3 plugs, which should be approximately 3 times the draw of any single plug. When you read the current draw between the first and second plugs, you are reading the current draw of only 2 plugs, which should be approximately twice that of a single plug. And the measurement between the second and third plug is measuring the draw of the 3rd plug only -- a single plug.

So, if the third is drawing 5.7 amps, I would expect two to draw approximately 11.4 amps and 3 to draw approximately 17.1 amps. Plus or minus normal manufacturing tolerances, I'd say you are in the ball park.

Now, that said, the odd thing is that they are drawing any current at all since the indicator is not glowing. I wonder if a previous owner by-passed the indicator? It is my understanding that the B7100 glow plugs are rated at 10.5v. The 3 plugs are connected in series with the indicator to drop the battery voltage to the rated voltage.

If the indicator is by-passed, then the glow plugs are being fed with full battery voltage. Probably OK as a short-term emergency fix. My concern would be the extra voltage may eventually burn out the glow plugs, or at least, age them prematurely.

 

[North Idaho Wolfman]

My glow plug indicator does not glow but tractor does start.

My tractor is an early 1970 model (3,000 hours), gear driven not hydraulic. I checked the amp current in the wires to the glow plugs. Wire from starting switch to first cylinder/glow plug next to bulkhead/firewall read 17.8 amps, wire to middle cylinder/glow plug 11.1 amps, third wire to last cylinder/glow plug next to radiator 5.7 amps.

Is the current drop through the wires normal? Any suggestions?

I will clean the wire connectors and see if that helps.

Thanks,

Mike from Cleveland.

Yes the amp loss is normal as you are loosing one glow plug out of the draw numbers's at each point where you are measuring.

If the indicator is bad, replace it, as it's part of the glow circuit.

 

[kubotasam]

Try it at night or in a dark garage. I bet the indicator just does not get bright enough to see it. And/or connect a voltmeter between one of the glowplugs and a good ground. When the key is in the preheat position you should see between 9 and 10 volts DC. If the indicator has been bypassed you will get closer to battery voltage in the preheat position. I have a B7100 that I have had for about 10 years. It starts great even in the cold. I do not see the indicator glow unless it is dark out. They are great tractors.

 

[mik1315]

kubotasam, North Idaho Wolfman, torch;

Thank you for the replies. Tonight I checked out the glow plug indicator and measured the voltage at each glow plug. The glow plug next to the fire wall/bulkhead measured 10.2 volts and the middle glow plug measured 7.1 and the glow plug next to the radiator measured 7.6 volts. Also I checked for glowing indicator at night and saw nothing. I think this case is closed and I ordered a new glow plug indicator.

Mike from Cleveland