Puzzled by start circuit

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jjgurley
40C crawler
40C crawler
Posts: 18
Joined: Wed Nov 15, 2017 12:47 pm

Puzzled by start circuit

Post by jjgurley » Sat Dec 16, 2017 4:07 pm

My start circuit isn't working right now. I can start it by jumping the solenoid, so I assumed it was the neutral safety switch, which was recently repaired by a shop. The machine is "on call" for driveway grading right now, so I hesitate to take it to too far apart.

My 450C manual (for SN 355844) say says my wiring runs from the key switch to the start button to the neutral switch to the solenoid. Thinking it could just as well be be the starter button, I opened the front panel, and put a meter across the start button. The results were not what I would expect, and I'm now doubting the wiring.

When still wired into the harness, I get the following readings (with ignition switch off):
1 - Switch not pushed - 5 ohms
2 - Switch pushed - 0 ohms
3 - Switch not pushed and shift lever not in neutral - open circuit
4 - Solenoid S terminal to ground - 1/2 ohm (regardless of shift lever)

#1-#2 tells me the start switch is functional.
#1-#3 tells me the safety switch is functional
#4 is completely confusing.

If the neutral switch is actually two wire, then #1 says that the wiring makes it all the way to the solenoid. I've seen some older wiring diagrams that show the neutral switch as a single wire (plus ground). The Deere manuals are very secretive about the actual wiring.

Does anyone know how the wires route around the machine? The actual pin numbers of the junction connector or at least wire color would be handy. My machine has been spray painted so many times that all the wires are yellow, but I can probably scrap the paint off. They're also pretty stiff and brittle. I know I need to dismantle it a little further, but it needs to stay available for a few more days until it rains.
1981 450C
6405 #355834

B Town
1010 crawler
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Posts: 300
Joined: Fri Dec 11, 2015 7:04 pm
Location: Western Iowa

Re: Puzzled by start circuit

Post by B Town » Sat Dec 16, 2017 8:18 pm

Take the left floorboard out, the neutral switch is under the left floorboard, on the side of the transmission case. Hope that helps, Bruce

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amos
1010 crawler
1010 crawler
Posts: 360
Joined: Thu Aug 11, 2016 7:29 am
Location: Piney Woods of east Texas

Re: Puzzled by start circuit

Post by amos » Sun Dec 17, 2017 8:38 am

Morning JJ,
I'm old and still have all of my pieces and parts(some showing wear though) and like things simple.I see all safety switches as a result of a loss to some slick lawyer's lawsuit.Mechanical lock outs I view as pertinent though. Neutral safety switch is an attempt to idiot proof a machine. Here's a thought: put the machine in neutral before starting it and just to be doubly sure depress clutch and make sure HLR is mechanically locked in neutral as well.
I've got a few modern pieces of equipment I do not operate daily and each and every time I try to start one I spend a few minutes making sure this interlock is working correctly or that interlock is in correct position. Then I still make sure it's in neutral and depress the clutch(just good practice).
With all of that being said when working on older equipment having wiring issues the first think I do is bypass all electrical interlocks and get back to basics.
Start circuit is basic: Key on and 12 volts going to fuel solenoid on injection pump.Key to start and energize starter solenoid or key to on and press start button to send 12 volts to starter solenoid.
Rest of circuit (lights,alternator,etc)is simple as well.
Note on gauges: I love mechanical oil pressure gauge,same on temp. Charge indicator lamp for alternator is fine but checking charging voltage with a meter is more accurate.
I fix my equipment for working purposes and not as historically accurate and correct restorations. A "correct" JD oil pressure gauge is well over $100.00 and an after market and accurate gauge that fits the hole is $20.00.
Side note: I buy,fix,and sell equipment and lately my buying has stopped because older mechanical (no computers or worse a DEF system) is selling extremely strong with little room for me to fix and charge a higher price. All because small to mid-sized users can't or won't spend the money to have a computer diagnostic whiz on staff for don't want to pay the $200.00+ an hour service call fees.
Neither way is right or wrong: all depends on what you're looking to do.
Amos
Pushin hard or diggin deep life is good.
What's ahead is what matters. What's behind is already done.
A fool of a man is he who doesn't ask questions...
God gave us 2 ears and 1 mouth for a reason...

jjgurley
40C crawler
40C crawler
Posts: 18
Joined: Wed Nov 15, 2017 12:47 pm

Re: Puzzled by start circuit

Post by jjgurley » Tue Dec 26, 2017 7:58 am

Unfortunately, just my desktop PC, taking everything apart and probing the problem fixed it. I did find a few more puzzles during the search though:

1) The bulkhead connector between the instrument panel and the engine compartment has ten wires on the engine side but only eight on the rear side. The back of the connector didn't want to come off (looks like a big sleeve of shrink tubing), so I didn't want to destroy anything, so the mystery remains.

2) The wire for the sensor for the spin-on hydraulic filter goes through the firewall without using the connector. Maybe when they added the sensor at SN 355xxx they got sloppy? Or maybe the wire failed and a bypass was added? Not carefully routed - in fact, was suffering from a nasty gash and might have been open.

Whatever the original problem, it will probably come back...
1981 450C
6405 #355834

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amos
1010 crawler
1010 crawler
Posts: 360
Joined: Thu Aug 11, 2016 7:29 am
Location: Piney Woods of east Texas

Re: Puzzled by start circuit

Post by amos » Tue Dec 26, 2017 8:32 am

Ah ha: dirty/corroded connectors strike again! Common problem with old machines. Your disconnecting and reconnecting rubbed off enough corrosion and or filth to get them to function again.Lots of guys slather on some dielectric grease and that does help a bit.Chaffed wires common too: just cover with tape and move on.
I've been deep cleaning a JD non-crawler and first my amp warning idiot light wouldn't go out and hyd oil high temp wouldn't go on in light test mode. After pressure washing again amp warning light working as it should and hyd oil high temp light won't go out(oil is cold).Crossed wires,bad ground,bad sender,loose wire: who knows...Just another reason why I avoid modern machines with even the most rudimentary computer systems much less those with complex computer controls. I swear engineers thought;" Let's tie everything together with sensors,circuits,relays,and software,put it in the most harsh environment there is and see what happens.....Looks good on paper so what can go wrong?".
Amos
Pushin hard or diggin deep life is good.
What's ahead is what matters. What's behind is already done.
A fool of a man is he who doesn't ask questions...
God gave us 2 ears and 1 mouth for a reason...

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