Deere STX38 will not start with the key [Solved]

[bgsengine]

Here's the real danger: IF your aftermarket switch is the wrong one and is designed for 12V ignition systems, it will do as you describe and count yourself lucky that it has not sent 12V to the magneto coil - If you had a 12V igntion switch it would be sending 12V to the Ign circuit ( which in your switch wiring may be hooked to something else) and when turned to OFF position, would be an open circuit to the magneto, but gets grounded in "run" Might need to do a reverse lookup of your part number to make sure it definitively applies to the machine AND the current engine (could it have had an engine swapped out? - so the factory switch may have been swapped out too to work with the replacement engine?)

Might could be you need to do a little ohms testing at your switch connector and see *WHICH TERMINAL* gives continuity to the MAGNETO GROUND and then you know which pin on the switch is the Mag wire, and again using the multi meter you can determine where that pin switches to in the different pin positions... it'd give you a solid starting point to diagnose further.

[Arkie]

Here's the real danger: IF your aftermarket switch is the wrong one and is designed for 12V ignition systems, it will do as you describe and count yourself lucky that it has not sent 12V to the magneto coil - If you had a 12V igntion switch it would be sending 12V to the Ign circuit ( which in your switch wiring may be hooked to something else) and when turned to OFF position, would be an open circuit to the magneto, but gets grounded in "run" Might need to do a reverse lookup of your part number to make sure it definitively applies to the machine AND the current engine (could it have had an engine swapped out? - so the factory switch may have been swapped out too to work with the replacement engine?)

Might could be you need to do a little ohms testing at your switch connector and see *WHICH TERMINAL* gives continuity to the MAGNETO GROUND and then you know which pin on the switch is the Mag wire, and again using the multi meter you can determine where that pin switches to in the different pin positions... it'd give you a solid starting point to diagnose further.

Right on! I was thinking the same about possibily frying the magneto and wiring loom.
Magneto system ignition switches apply a ground to the mag wire when switch to off and a open circuit to the magneto kill wire in start and run. 12v coil systems apply 12v when starting and in run and a open circuit when turned to off.

If you are not careful, as bsengine suggests, you can very easily with the wrong ignition switch apply 12v to the kill wire going to the magneto and let out the majic smoke, ruin a $60+ mag plus burn up some wiring. (the kill wire and the magneto will not live very long with 12v applied to it's primary)

If the electrical diagram you are using actually matches the machiney you might try PM'ing me a copy and I'll see if I can walk you thru it, maybe. I've been deep into electrical, electronics, goat roping, fishin, huntin and mechanics for 50 years but I can't seem to locate a exact online wiring diagram for your machine, because online shows several versions. Also sometimes the parts diagrams klisting for equipment (at the supply parts house and from a manufacturer is not completely correct and you end up getting the wrong parts due to different parts being installed from manufacturer during the same year for same piece of eq. (Same model and year of vec's using different parts is a common thing)

[aceatpool]

Thanks bsengine & arkie for the comments. I suppose I WAS extremely lucky I didn't toast something. Due to my inexperience I assumed (ass outta u & me) that the aftermarket was the same as the JD since it "looked" the same. It wasn't until this running in the "off" position presented itself did I investigate & found the grounds were different. I went this AM to the dealer & asked to speak to a mechanic. I explained my dilema & he was unable to suggest a definitive cause. He said he has seen switches bad from the factory but his best guess was the brake safety was faulty or not adjusted properly. Since I didn't want to make another 70 mile round trip back to the dealer I purchased another JD ign switch ($28) just in case???
I did the brake safety continuity checks (per manual) & got the readings specified. I thought that maybe the park break linkage was worn allowing the pedal to spring back off the switch just enough to leave it "open". That was not the case. I installed the 3rd new switch and NOTHING!!! The last sentence in that procedure was "if the operation is correct test switch" ARRGGHHH!!!
I don't have the equipment to scan/post photos etc. Best I can do is let ya'll know I'm using JD TM1561 (15Mar97). The procedure I've been using is on page 4-69 and 4-70.

[38racing]

If you have alligator clips on the VOM leads or get some test leads with a clip on each end then it's pretty easy to test the switch. And to switch wires around but leave it obvious use one of these
https://www.bantasaw.com/catalog/viewpr ... 205&p=1326
Remove the existing connector from the switch and put the above connector on the keyswitch and then put a spade connector on the wire ends and plug the appropriate wire in the expected slot in the original connector.
But this is based on your problem being wrong switch connections , not some other circuit problem.

[aceatpool]

Not sure what was the problem. Could be inexperience at troubleshooting??????? I decided to begin again on the diagnosis. Saw the start switch harness had some dirt/grease on the outside but the terminal receptacle looked pretty clean. Just on a whim I decided to clean the harness anyway. Dried everything off installed the new JD switch & it started/ran/moved & mowed!!! Not sure the cleaning made any difference but it runs now. Go figure????? Took the jumper out of the brake safety harness & installed the wires back on the switch in its' normal position. Machine still started & ran OK. Guess I'll see if it starts OK tomorrow or will the "mystery" problem reappear????
Thanks bunches to ALL who responded. Again I know how hard it is to diagnose from long distance.