Voltage at Solenoid

rtrtrtrtrt

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My dad's mower will not start, just happened out of the blue. John Deere SRX75 rider, about 1993 model.
Have 12 volts at (4 post) solenoid wire end from ignition per multimeter when key is turned.
Can jump from POS terminal to solenoid ignition post and it starts right up.
Replace wire on solenoid, turn key and nothing.

Can I be losing the 12 volts from the ignition for some reason when the load of the solenoid is put on it? This has me baffled since I always show 12 v coming through wire from ignition when key is turned but does not start when connected to solenoid. Have bent and wiggled wire while checking with meter and have constant 12v, have not removed ignition key switch assembly and tested for continuity.

thanks for any ideas or assistance
 

bertsmobile1

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A 4 post solenoid has 2 big terminals being battery power & switched power to the starter and 2 thin control wires at the bottom being a + 12V and a ground.
Most have another wire attached to the hot terminal which is the 12 V supply to the rest of the mower ( saves wire ) .
On many 4 pole solenoids both the + 12 V control wire & the ground control wire are switched.
If yours is like that then try running a light jumper from the + terminal to the + control wire and then with a jumper from ground to the ground control wireYou can check the solenoid itself by disconnecting both control wires and jump one + the other ground.
The control wires are not polarity sensititive but the rest of the mower wiring is.
From memory yours are purple ( +) and black (-) if it is a 4 pole.
 

rtrtrtrtrt

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A 4 post solenoid has 2 big terminals being battery power & switched power to the starter and 2 thin control wires at the bottom being a + 12V and a ground.
Most have another wire attached to the hot terminal which is the 12 V supply to the rest of the mower ( saves wire ) .
On many 4 pole solenoids both the + 12 V control wire & the ground control wire are switched.
If yours is like that then try running a light jumper from the + terminal to the + control wire and then with a jumper from ground to the ground control wireYou can check the solenoid itself by disconnecting both control wires and jump one + the other ground.
The control wires are not polarity sensititive but the rest of the mower wiring is.
From memory yours are purple ( +) and black (-) if it is a 4 pole.

Thanks. I have already used jumper directly from + terminal on battery to control post on solenoid (with solenoid ground left connected, and with seperate ground) and mower starts right up so I know the solenoid itself is working.
 

bertsmobile1

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OK so what are the colours of the control wires on the solenoid and what do they show when you test them.
As mentioned previously. one should go from open to 12 V and the other should go from open to ground,
You could have a bad switch , bad relay or bad wiring but without some more information we can be of no further use.
From your original post it reads you have power to the control wire at all times .
 

rtrtrtrtrt

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Sorry if I'm not clear. Mower is an hour away at dad's and I'm at work so can't verify wire colors. I'm thinking this must be a bad safety switch.

If solenoid is as follows;
(A) large terminal, +12v from battery
(B) large terminal, solenoid switched/controlled +12v to starter
(C) small terminal, +12v from ignition when key is in "START" position
(D) small terminal, solenoid to ground

I can jump from + battery terminal to (C) with key in "ON" position and mower starts so solenoid, starter, etc are good. I'm assuming that with key in "ON" position vs "START" all safety switches are closed or out of the circuit.

A meter put on the wire from ignition to (C) showed 12v when key is in "START" position, however meter was grounded to battery terminal. I did not think to test with meter grounded to (D).

Do safety switches work by interrupting ground as opposed to preventing 12v from being sent to (C)? In other words they are between (D) and ground? If so that would explain why I always read 12v at (C) when grounding meter elsewhere but mower does not start when (C) & (D) are connected and switches are in the line and preventing (D) from reaching ground. If so I'm thinking I should be able to use jumper from (D) directly to ground thus bypassing switches and start mower thus confirming bad switch somewhere between (D) and ground.

Thanks again for your time and assistance
 

bertsmobile1

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Sorry if I'm not clear. Mower is an hour away at dad's and I'm at work so can't verify wire colors. I'm thinking this must be a bad safety switch.

If solenoid is as follows;
(A) large terminal, +12v from battery
(B) large terminal, solenoid switched/controlled +12v to starter
(C) small terminal, +12v from ignition when key is in "START" position
(D) small terminal, solenoid to ground

I can jump from + battery terminal to (C) with key in "ON" position and mower starts so solenoid, starter, etc are good. I'm assuming that with key in "ON" position vs "START" all safety switches are closed or out of the circuit.

A meter put on the wire from ignition to (C) showed 12v when key is in "START" position, however meter was grounded to battery terminal. I did not think to test with meter grounded to (D).

Do safety switches work by interrupting ground as opposed to preventing 12v from being sent to (C)? In other words they are between (D) and ground? If so that would explain why I always read 12v at (C) when grounding meter elsewhere but mower does not start when (C) & (D) are connected and switches are in the line and preventing (D) from reaching ground. If so I'm thinking I should be able to use jumper from (D) directly to ground thus bypassing switches and start mower thus confirming bad switch somewhere between (D) and ground.

Thanks again for your time and assistance

Thank you very much for the better description,
people forget you are there & I ( for example ) am at least 8,000 miles away so I can only work with what you tell me.

I do not have a SX/SR manual so can not be sure which wiring set up you have,
Generally the + feed to the solenoid terminal C goes through the starter switch, through the PTO switch through the brake switch then to the solenoid.
All of these are pass through switches in a chain, one not connection = nothing
Your dads mower looks like it has a neutral switch which powers a relay which breaks the ground connection to terminal D.

A but hard to tell because when I search for wiring diagrams I get a dozen variations.
That is why in the original post I asked you to try it with D jumpered to a good ground which would have covered all bases.
Some diagrams showed 2 relays and some showed 1 relay.

Unlike the other mower companies JD make excellent manuals with step by step instructions for both fault finding and repairs.
They can be downloaded at a small cost or ordered as a paper copy for a much higher cost from the JD web site.
Excellent value for money.
When I sell a used JD I include the technical manual with the mower and people pay near twice the price as ones without the manual go for.
 

rtrtrtrtrt

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Just FYI - this turned out to be a problem with the PTO switch. It was apparently bad but still making enough contact to allow 12v through as long as it was not under load so when checking with meter at solenoid I always got good reading but no start. Thanks again for your help, have a great weekend.
 
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