Buddy has an John Deere LA120. Will not crank. With the key off there is continuity to ground on the solenoid terminal. When you turn the key on that ground is lost yet it is wired directly to the neg battery cable. Can anyone give me some direction?
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
LA120 loses ground
- Thread starter Mortten
- Start date
More options
Export threadbertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 64
- Messages
- 24,705
Mort
What solenoid terminals where ?
The Solenoid switches POWER from the battery to the starter motor
Thus the top two big terminals should be battery voltage on one side and nothing on the other till the key goes to the start position when battery voltage is switched to the starter motor
At the base will be either 1 or 2 small tab terminals
If only one it will be open then go battery voltage to trigger the solenoid to switch the power to the starter
If there are 2 tabs at the bottom then one will work as above and the other will be be either ground all the time or be open and go ground when the the key is turned to the start position
From what you have written it sounds like the battery has been connected wrong way around .
What solenoid terminals where ?
The Solenoid switches POWER from the battery to the starter motor
Thus the top two big terminals should be battery voltage on one side and nothing on the other till the key goes to the start position when battery voltage is switched to the starter motor
At the base will be either 1 or 2 small tab terminals
If only one it will be open then go battery voltage to trigger the solenoid to switch the power to the starter
If there are 2 tabs at the bottom then one will work as above and the other will be be either ground all the time or be open and go ground when the the key is turned to the start position
From what you have written it sounds like the battery has been connected wrong way around .
One small terminal is always grounded as the solenoid is not grounded through the base. With the switch off that terminal has continuity to ground as it should. When the switch is is any other position that continuity is lost thus rendering the solenoid inoperable because it lacks a ground. Very odd.
bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 64
- Messages
- 24,705
No it is quite normal.
The concept of ground switching is foreign to a lot of people
All electrical circuits are a loop
Power source ( battery ) to item & back to battery.
You can put the switch either before the item ( on what we call the power side ) or after the item ( what we call the ground side )
The item does not care where the circuit is switched all it sees is an incomplete circuit .
Most of the switches on mowers are ground switches
So in your case I think , ( because I am too busy right now to check the manual ) the brake switch makes the ground to the solenoid thus you can not crank the engine unless the parking brake is on, standard safety feature.
JD put out an excellent Technical Manual for your mower with very detailed instruction of what to test where to test it & how to test it plus what the test results mean, where all of the parts are hidden and how everything actually works.
It costs about the same as 1 to 2 billed hours for a tech which is what a shop will charge you for diagnosing the problem + the actual repair + pick up & delivery so it is actually very cheap as a digital download from the JD web page .
There is no excuse for any JD owner not having one apart from being too cheap for their own good
The concept of ground switching is foreign to a lot of people
All electrical circuits are a loop
Power source ( battery ) to item & back to battery.
You can put the switch either before the item ( on what we call the power side ) or after the item ( what we call the ground side )
The item does not care where the circuit is switched all it sees is an incomplete circuit .
Most of the switches on mowers are ground switches
So in your case I think , ( because I am too busy right now to check the manual ) the brake switch makes the ground to the solenoid thus you can not crank the engine unless the parking brake is on, standard safety feature.
JD put out an excellent Technical Manual for your mower with very detailed instruction of what to test where to test it & how to test it plus what the test results mean, where all of the parts are hidden and how everything actually works.
It costs about the same as 1 to 2 billed hours for a tech which is what a shop will charge you for diagnosing the problem + the actual repair + pick up & delivery so it is actually very cheap as a digital download from the JD web page .
There is no excuse for any JD owner not having one apart from being too cheap for their own good
I do understand ground switching. How this tractor is wired is this:
Ground cable goes from battery to the frame. A wire crimped into the same lug as the ground cable goes behind the engine to a splice. From the splice wires go to the solenoid and the headlights. Basically a straight shot from battery to solenoid. I’ll tell my buddy to get a manual.
Ground cable goes from battery to the frame. A wire crimped into the same lug as the ground cable goes behind the engine to a splice. From the splice wires go to the solenoid and the headlights. Basically a straight shot from battery to solenoid. I’ll tell my buddy to get a manual.
A couple other curiosities. When the brake is depressed and locked, the lights don’t work. When released they do. When you turn the key to lights/run the hour meter comes on. When you turn it to run the hour meter goes off. I’m thinking maybe ignition switch.
bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 64
- Messages
- 24,705
Yes there is more to this than meets the eye which is why you really need to look at a wiring diagram
JD have a funny habit of changing the colour code of the wires each time they go through a switch or relay .
So for instance solid black to the brake switch then black & white to the PTO switch then back to solid black to the solenoid
Thus you see full back at both ends and assume the wiring is direct when in fact it has been through a few switches first.
The overall colour usually remains the same but the trace colour can change a few times
There is no wiring standard for mowers however a while back there was a plan handed down from the courts to make all wires plain black to prevent people bypassing safety switches and causing injury to others
The hour meter on most JD's is grounded to the G terminal on the key switch and gets power from the A ( alternator ) terminal on the key switch
Now the ground to the key switch is some times a direct wire to a common grounding point or just a short wire from the body some where to the key switch which can come loose, fall off or fracture inside the insulation .When this happens the ground to the key switch will be backwards from something down stream of the key switch which of course will not be ground all of the time like the PTO switch. MIR cut out switch, seat switch or parking brake switch o even the magneto kill wire itself .
Some take power feed for the Hour meeter from the PTO switch singularly so they record mowing hours not engine hours while others will be connected to both so they measure both engine hours & running hours and will turn off if you leave the key turned on all week .
I thought I had an LA manual but I don't .
JD also have different circuits depending upon which engine is fitted so it gets even more confusing .
Once the shock of pays for the manual wears off your friend will be very pleased with the 300+ pages and become an overnight expert.
JD's are one of the few mowers I will recondition & sell second hand
When I do I include a printed copy of the manual with the mower spiral bound in a nice folder and add around $ 300 to the price.
They usually sell within a day or so
And one person who bought one like that from me now actively seeks out STX's which he reconditions & sells ( I remembered his ebay name )
Toro manuals are also quite good and are a free download but of course as they are free they are nowhere near as detailed as the JD ones
Another reason to stick with JD & Toro
JD have a funny habit of changing the colour code of the wires each time they go through a switch or relay .
So for instance solid black to the brake switch then black & white to the PTO switch then back to solid black to the solenoid
Thus you see full back at both ends and assume the wiring is direct when in fact it has been through a few switches first.
The overall colour usually remains the same but the trace colour can change a few times
There is no wiring standard for mowers however a while back there was a plan handed down from the courts to make all wires plain black to prevent people bypassing safety switches and causing injury to others
The hour meter on most JD's is grounded to the G terminal on the key switch and gets power from the A ( alternator ) terminal on the key switch
Now the ground to the key switch is some times a direct wire to a common grounding point or just a short wire from the body some where to the key switch which can come loose, fall off or fracture inside the insulation .When this happens the ground to the key switch will be backwards from something down stream of the key switch which of course will not be ground all of the time like the PTO switch. MIR cut out switch, seat switch or parking brake switch o even the magneto kill wire itself .
Some take power feed for the Hour meeter from the PTO switch singularly so they record mowing hours not engine hours while others will be connected to both so they measure both engine hours & running hours and will turn off if you leave the key turned on all week .
I thought I had an LA manual but I don't .
JD also have different circuits depending upon which engine is fitted so it gets even more confusing .
Once the shock of pays for the manual wears off your friend will be very pleased with the 300+ pages and become an overnight expert.
JD's are one of the few mowers I will recondition & sell second hand
When I do I include a printed copy of the manual with the mower spiral bound in a nice folder and add around $ 300 to the price.
They usually sell within a day or so
And one person who bought one like that from me now actively seeks out STX's which he reconditions & sells ( I remembered his ebay name )
Toro manuals are also quite good and are a free download but of course as they are free they are nowhere near as detailed as the JD ones
Another reason to stick with JD & Toro
Gord Baker
Well-Known Member
- Joined
- Aug 21, 2018
- Threads
- 1
- Messages
- 349
Carefully clean ALL battery and Solenoid cable connections.
Very carefully -with cap ON fuel tank- connect one booster cable to Positive on Battery and touch big connector on Starter Motor with the other end of same cable. There will be sparks. If it cranks, you may need a new Solenoid or Ignition switch. Be sure safety switch on Brake is operating correctly. MOVE the plunger in and out.
Very carefully -with cap ON fuel tank- connect one booster cable to Positive on Battery and touch big connector on Starter Motor with the other end of same cable. There will be sparks. If it cranks, you may need a new Solenoid or Ignition switch. Be sure safety switch on Brake is operating correctly. MOVE the plunger in and out.