Kubota ZD21 needing starting/wiring help

[fortillian]

My grandpa has a Kubota ZD21 and was mowing and snagged a tree and it pulled the battery from the tray and now it won't start. I found this ground wire that seems to be the issue, when reconnected I can get the mower to try and start, but this wire starts burning. I know I need to replace this whole wire, just wondering if anyone can help me figure out where it leads. I suspect the starter. It doesn't start to smoke until you engage the starter. When the key is in the On Position, and in the Energize Glow Plug position it doesn't smoke, only when you turn the the Start Position. Any help is appreciated.

Here is a link to the service manual I am viewing, the starting electrical circuit is on page 209

Thanks

 

[Dustyx2]

The original battery fit in that tray and had a cover. The negative battery terminal is where your picture shows the positive terminal of a wider and shorter battery. The negative cable grounds to the frame right behind the battery tray. The positive crosses under the engine and goes direct to the starter. You either need to get the correct battery for that so the cover fits on it or figure a way to tie that battery down.
The original is an odd size. Probably why its the way it is.

 

[Russell King]

Not sure what wire you are describing.

From the battery positive terminal the large battery cable does go directly to the starter solenoid.

If that is smoking then it will need to be replaced.

But you say that you are concerned with the ground wire. The battery ground wire normally goes from the battery negative post to a ground point on the frame or the engine. That point could be a bolt on the starter but that would be unusual to me and not standard factory wiring.

Please describe what wire is smoking if it is NOT the large positive battery cable (that may not be red in color)

 

[Dave_eng]

I have marked up one of the original photos. Does my RED box surround the burned wires?

You need to open up the corrugated plastic covers where I marked with yellow lines so that wire colors can be seen.

Dave

 

[vernon_hill]

I had the same melted wires, the all appear to be grounds. I spliced in new wires, replaced the combi box ad the starting switch. Jumped out all of the safety switches and it still wont start. i am only getting 9.6 volts out of the ingnition switch, and the same at the starter relay. I have the whole wiring harness opened up and don't see any burned or cut wires. It will start once in a while like every 5-10 times i turn the key... If anyone has any suggestions i would be grateful.

 

[lugbolt]

I had the same melted wires, the all appear to be grounds. I spliced in new wires, replaced the combi box ad the starting switch. Jumped out all of the safety switches and it still wont start. i am only getting 9.6 volts out of the ingnition switch, and the same at the starter relay. I have the whole wiring harness opened up and don't see any burned or cut wires. It will start once in a while like every 5-10 times i turn the key... If anyone has any suggestions i would be grateful.

check the ground wire between the frame and the engine. If it's not grounding good, it'll let the smoke out of other wires. Electrons take the path of least resistance; if that just happens to be a little 16ga wire, the high current required to run the starter WILL burn that little 16ga wire, quickly.

Learn to do a voltage drop test also, it'll save you TONS of time diagnosing.

 

[vernon_hill]

Thanks for the trouble shooting tip. I never thought to trouble shoot from that perspective. I think i know what you were talking about. I put one lead on the + side of battery and checked all of the grounds at the other end of the wiring harness and got 12 volts on all of them.

took the ground off of the frame behind the battery and used the wire wheel to clean the metal and put it all back together. No change. Solenoid clicks but starter won't turn. Checked the voltage and it is 9.6 volts.

 

[lugbolt]

do a voltage drop test.

Put one probe of your digital volt-ohm meter (DVOM) on the battery, start with the negative post. Take your other probe and put it on the starter mounting bolt. Polarity of the probes does not matter, just set it to DC Voltage. Now hit the starter switch and read your volt meter. If it says 1.925v, that is your voltage drop. You don't want to see much more than a volt drop on that system, under load. Voltage drop test is done under load. Why? Because ONE strand of copper wire can conduct enough electricity such that a standard continuity test will come back 0.0 ohm; but once you put the system under a load, that single strand won't carry enough amperage to do what needs to be done. Corrosion can cause the same thing and I've seen more than one ZD mower with corrosion INSIDE the wires' insulation. The only way you find that is (1) cut all the wiring open and look for yourself, or (2) a voltage drop test. Or I guess (3), hold the load on the wiring until something goes up in smoke and then whatever you just burnt is a problem. Whether it was "the" root problem, who knows.

Keep in mind you can do it on ground side, and you can do it on positive side. Polarity of the probes does not matter on a DVOM. For instance you can put the dvom lead on the positive battery post, and the other probe you can use at the starter positive post. Hit the key and read it-if it's 0.5v or less, it's fine. Ideally you'd want to see 0.200v or less but 1v on this system will be ok. If it's reading something like 2.8v, you have a drop somwhere between the positive battery post and the starter post, indicating either the wire is corroded/broken/bad, or possibly a bad connection.

Those are just examples, but this test, done with patience, will find the problem.

 

[DustyRusty]

Is it possible that the starter was damaged at the same time the wire was caught by the tree?

 

[GreensvilleJay]

I suspect the big,fat GROUND cable from the battery isn't solidly 'grounded' to the engine, when this happens a LOT of current will try to go through other grounds ( little black wires ) to spin the starter.
I don't know HOW it's actually wired, some battery 'ground' goes to a frame then another cable from the frame to the engine. Riding mowers are terrible with 'ground' from battery to engine.BTDT,too many times.

 

[Dustyx2]

As I recall there is one ground from the battery to the frame and then on the starter side of the engine is another ground cable from the frame to the engine. I would check that one out too.

 

[vernon_hill]

Starter turns with little effort and a jumper to the trigger terminal.

 

[vernon_hill]

absolutely right. There is a ground on the other side from the frame to a piece of square tube bolted to the engine. See attached. Cleaned both sides and put it back together no change.

 

[vernon_hill]

I suspect the big,fat GROUND cable from the battery isn't solidly 'grounded' to the engine, when this happens a LOT of current will try to go through other grounds ( little black wires ) to spin the starter.
I don't know HOW it's actually wired, some battery 'ground' goes to a frame then another cable from the frame to the engine. Riding mowers are terrible with 'ground' from battery to engine.BTDT,too many times.

Big ground wire solid. Pulled it, ran wire wheel, and put 3 wires back on bolt.

 

[vernon_hill]

do a voltage drop test.

Put one probe of your digital volt-ohm meter (DVOM) on the battery, start with the negative post. Take your other probe and put it on the starter mounting bolt. Polarity of the probes does not matter, just set it to DC Voltage. Now hit the starter switch and read your volt meter. If it says 1.925v, that is your voltage drop. You don't want to see much more than a volt drop on that system, under load. Voltage drop test is done under load. Why? Because ONE strand of copper wire can conduct enough electricity such that a standard continuity test will come back 0.0 ohm; but once you put the system under a load, that single strand won't carry enough amperage to do what needs to be done. Corrosion can cause the same thing and I've seen more than one ZD mower with corrosion INSIDE the wires' insulation. The only way you find that is (1) cut all the wiring open and look for yourself, or (2) a voltage drop test. Or I guess (3), hold the load on the wiring until something goes up in smoke and then whatever you just burnt is a problem. Whether it was "the" root problem, who knows.

Keep in mind you can do it on ground side, and you can do it on positive side. Polarity of the probes does not matter on a DVOM. For instance you can put the dvom lead on the positive battery post, and the other probe you can use at the starter positive post. Hit the key and read it-if it's 0.5v or less, it's fine. Ideally you'd want to see 0.200v or less but 1v on this system will be ok. If it's reading something like 2.8v, you have a drop somwhere between the positive battery post and the starter post, indicating either the wire is corroded/broken/bad, or possibly a bad connection.

Those are just examples, but this test, done with patience, will find the problem.

working on this now. i am a little confused by the "start with the negative post. Take your other probe and put it on the starter mounting bolt. " but i am about to try it.

 

[vernon_hill]

working on this now. i am a little confused by the "start with the negative post. Take your other probe and put it on the starter mounting bolt. " but i am about to try it.

ok so starter mount bolt to negative battery post = .051VDC.

The issue is the trigger terminal is only getting 7.5 volts now. See attached. Where do I go next?

 

[vernon_hill]

ok so starter mount bolt to negative battery post = .051VDC.

The issue is the trigger terminal is only getting 7.5 volts now. See attached. Where do I go next?

not smart enough for voltage drop. Please take a look at the attached.

 

[GreensvilleJay]

only getting 9 instead of 12 would indicate the ignition switch contacts are 'bad'.
could be grease buildup, not allowing full voltage.
I've seen that on power window switch in my truck.
you 'might' get lucky by spraying wd40 in where the key goes and several 'turns of the key' to 'flush the grease down and out. try 4-5 times, see if luck is on your side.
You should check the wire but it only goes from the switch to the OPC box, a relay contact, so unlikely it's 'loading down' the +12 to only 9. Easy (?) to check. remove wire at ign switch and check post with meter when you turn key to start. should get +12. If 9, then switch is 'bad'.

 

[vernon_hill]

only getting 9 instead of 12 would indicate the ignition switch contacts are 'bad'.
could be grease buildup, not allowing full voltage.
I've seen that on power window switch in my truck.
you 'might' get lucky by spraying wd40 in where the key goes and several 'turns of the key' to 'flush the grease down and out. try 4-5 times, see if luck is on your side.
You should check the wire but it only goes from the switch to the OPC box, a relay contact, so unlikely it's 'loading down' the +12 to only 9. Easy (?) to check. remove wire at ign switch and check post with meter when you turn key to start. should get +12. If 9, then switch is 'bad'.

Yeah that is kind of what I thought. I replaced the switch with a brand new one from Kubota. This thing is kicking my butt. One of the red wires at the connector closest to the switch looked compromised so I ran a jumper from the connector to the starter, essentially replacing the main hot wire. and it started five times in a row. Wrapped up the wiring and it stopped working again. ugh....

 

[vernon_hill]

My grandpa has a Kubota ZD21 and was mowing and snagged a tree and it pulled the battery from the tray and now it won't start. I found this ground wire that seems to be the issue, when reconnected I can get the mower to try and start, but this wire starts burning. I know I need to replace this whole wire, just wondering if anyone can help me figure out where it leads. I suspect the starter. It doesn't start to smoke until you engage the starter. When the key is in the On Position, and in the Energize Glow Plug position it doesn't smoke, only when you turn the the Start Position. Any help is appreciated.

Here is a link to the service manual I am viewing, the starting electrical circuit is on page 209

Thanks

View attachment 57521
View attachment 57522

hey bud, did you ever get that mower running? If so what was the fix?