John Deere 520 wiring diagram positive ground.

[Sherdon89]

I have a new 520 that had been setting in shed for years. and the wiring was getting tired. in replacing it I found brown wire extra from switch. found wiring diagram and it showed wire going to point side of coil (+) terminal. So with all that said, why would a wire from switch go to positive/point side of coil? and also tractor runs. Just don't like to make short cuts in history's great engineers designs. if that makes since. If the wire would have went to neg side of coil I would guessed it might be working as a resistor bypass to keep voltage up with lights in the on position. any thoughts would be helpful. Thank you.

 

[Loosehandle]

That wire is to give full voltage to the coil while cranking the engine, when running coil input goes through resistor

 

[Tx Jim]

Ditto

 

[620 John]

I'm pretty sure that brown wire is meant to ground out the coil to prevent starting while cranking the engine over with the key switch off. The wire that supplies full 12 volts to the coil while cranking comes from the starter switch down below mounted on the starter. My 620 used to have that wire but I took it off because if I remember right there was a grounding tab burned off that went from the key switch terminal to the key switch housing. I figured the wire might cause more problems than it will save so I took it off. However it will start without the key on but will die when I let off the starter pedal. I'll look at the diagram when I get home or maybe someone will post a diagram

 

[rvirgil_KS]

I'm pretty sure that brown wire is meant to ground out the coil to prevent starting while cranking the engine over with the key switch off. The wire that supplies full 12 volts to the coil while cranking comes from the starter switch down below mounted on the starter. My 620 used to have that wire but I took it off because if I remember right there was a grounding tab burned off that went from the key switch terminal to the key switch housing. I figured the wire might cause more problems than it will save so I took it off. However it will start without the key on but will die when I let off the starter pedal. I'll look at the diagram when I get home or maybe someone will post a diagram

I agree. My diagram shows black wire from starter switch to coil input to bypass resistor when cranking engine.

The brown wire comes from a mag terminal on the starter going to points side of coil. Mag should be grounded when switch is off.

 

[John T]

I agree with 620 John. The extra wire from switch is for a ground that kills the ignition if you crank it over even in the off position. There’s two wires on both sides of the coil as I recall. John T

 

[wore out]

I agree. My diagram shows black wire from starter switch to coil input to bypass resistor when cranking engine.

The brown wire comes from a mag terminal on the starter going to points side of coil. Mag should be grounded when switch is off.

"Mag terminal on the STARTER"?

 

[WTW]

I have a new 520 that had been setting in shed for years. and the wiring was getting tired. in replacing it I found brown wire extra from switch. found wiring diagram and it showed wire going to point side of coil (+) terminal. So with all that said, why would a wire from switch go to positive/point side of coil? and also tractor runs. Just don't like to make short cuts in history's great engineers designs. if that makes since. If the wire would have went to neg side of coil I would guessed it might be working as a resistor bypass to keep voltage up with lights in the on position. any thoughts would be helpful. Thank you.

I have a new 520 that had been setting in shed for years. and the wiring was getting tired. in replacing it I found brown wire extra from switch. found wiring diagram and it showed wire going to point side of coil (+) terminal. So with all that said, why would a wire from switch go to positive/point side of coil? and also tractor runs. Just don't like to make short cuts in history's great engineers designs. if that makes since. If the wire would have went to neg side of coil I would guessed it might be working as a resistor bypass to keep voltage up with lights in the on position. any thoughts would be helpful. Thank you.

Not to argue anybody but, If my memory is serves me right and I will get my Two Cylinder SM to verify when I get home. The primary ignition wire for the 12 volt bypass connects to the coil side of the resistor and the brown wire you are referring does connect to the point side of coil to ground point when shut off. Not sure there reasoning for this ground wire but I know I have seen this before on later two cylinders. The switch grounds points through the ignition switch at same time it cuts off power to ignition resistor. If I am correct, you do not connect this brown wire to resistor as it will burn it out. DW

 

[Pete in MD]

That wire is to give full voltage to the coil while cranking the engine, when running coil input goes through resistor

The resistor bypass is the wire that runs from the starter switch to the input ( - side) of the coil.
The brown wire Sherdon89 mentioned prevents the engine from starting when the ignition switch is turned off.

 

[PJH]

What 620 John sez! I don't have the wiring diagram in front of me, but there has to be a means to ground the coil when the starter switch is engaged, and the ignition switch is off. Someone could get hurt!

 

[John T]

Not to argue anybody but, If my memory is serves me right and I will get my Two Cylinder SM to verify when I get home. The primary ignition wire for the 12 volt bypass connects to the coil side of the resistor and the brown wire you are referring does connect to the point side of coil to ground point when shut off. Not sure there reasoning for this ground wire but I know I have seen this before on later two cylinders. The switch grounds points through the ignition switch at same time it cuts off power to ignition resistor. If I am correct, you do not connect this brown wire to resistor as it will burn it out. DW

I don’t have the diagram in front of me either nor know the colors but as I recall there are TWO wires on the coil input. One up from the starter switch that’s hot ONLY when starter switch is engaged. Its purpose is to supply hot non ballasted voltage to coil when cranking as it effectively by passes the ballast. The other is from the ign switch via the in series ballast so coil voltage is reduced to 6 for a 6 volt coil. Now two wires on coils output. One is to distributor and its points. Other is to the Mag/Ground on the ign switch so when switch is off yet starter switch is engaged there’s no spark. Like you I’m not here to argue but I believe that’s how it’s wired and how it works but I don’t know the wire colors if I’m wrong hope someone can correct this. Ps I’m talking about 12 volt tractors with a 6 volt coil plus ballast plus ballast by pass when cranking that use the mechanical saddle start switch with the extra small terminal hit when cranking that aired to coils input like some of the 20 series. John T. No warranty check the diagram and correct if wrong.

 

[John T]

What 620 John sez! I don't have the wiring diagram in front of me, but there has to be a means to ground the coil when the starter switch is engaged, and the ignition switch is off. Someone could get hurt!

That’s the same as I understand it see my response above John T

 

[rvirgil_KS]

"Mag terminal on the STARTER"?

"Mag terminal on the STARTER"?

oops! meant to say on switch

 

[620 John]

Not to argue anybody but, If my memory is serves me right and I will get my Two Cylinder SM to verify when I get home. The primary ignition wire for the 12 volt bypass connects to the coil side of the resistor and the brown wire you are referring does connect to the point side of coil to ground point when shut off. Not sure there reasoning for this ground wire but I know I have seen this before on later two cylinders. The switch grounds points through the ignition switch at same time it cuts off power to ignition resistor. If I am correct, you do not connect this brown wire to resistor as it will burn it out. DW

Now that you say that I remember now that the brown wire on my 620 was on the wrong side of the coil. Instead of it being on the points side it was on the resistor side of the coil. I think that's why it burned the ground tab off the key switch. The tractor was converted to negative ground and I'm guessing someone got confused and put the brown wire on that side when they switched the wires around at the coil.

 

[John T]

Now that you say that I remember now that the brown wire on my 620 was on the wrong side of the coil. Instead of it being on the points side it was on the resistor side of the coil. I think that's why it burned the ground tab off the key switch. The tractor was converted to negative ground and I'm guessing someone got confused and put the brown wire on that side when they switched the wires around at the coil.

Thanks for the update. The wire up from the starter switch is hot ONLY when switch is engaged. If it were connected to frame ground ?????? that was a dead short and could burn the wire or a terminal. If it was connected to the same voltage potential there wouldn’t be any current flow. The Mag/Ground terminal on the switch is grounded when switch is off Fun sparky chatting with you lots of things can happen when switching polarity maybe okay maybe not lol. John T. I think my explanation above is still true ???

 

[wore out]

I agree with 620 John. The extra wire from switch is for a ground that kills the ignition if you crank it over even in the off position. There’s two wires on both sides of the coil as I recall. John T

Makes 'ya wonder how that came to be... lots of other machines had "starting bypasses" and I don't recall any other brands having the safety ground across the breaker points while the ignition switch was "off".

It would be interesting to know how it came to be, a meticulous engineer who put it in place on the side of caution, or was there an "incident", either in "testing" or "in the field that prompted it.

Like Ford having the transmission-top neutral start safety switch on the "N" series almost from the beginning in 1939.

When did other brands adopt that safety feature?

 

[John T]

Makes 'ya wonder how that came to be... lots of other machines had "starting bypasses" and I don't recall any other brands having the safety ground across the breaker points while the ignition switch was "off".

It would be interesting to know how it came to be, a meticulous engineer who put it in place on the side of caution, or was there an "incident", either in "testing" or "in the field that prompted it.

Like Ford having the transmission-top neutral start safety switch on the "N" series almost from the beginning in 1939.

When did other brands adopt that safety feature?

I am not aware of any brands other than mother Deere who adopted that safety feature maybe it wasn’t needed because of different ignition, switching and ballast by pass circuitry. On deeres it was used with the saddle mount starter switches and ballast by pass method. I remember first learning why there were two wires on both sides of the coil and remember an incident when the switch was off on a 620 but when the starter was depressed it fired yikes scared me and later I found out that safety wire from Ground/Mag on the switch was missing !!! Fun sparky chatting with you John T