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I am in need of some help on my 420. I recently received it from my father. When I brought it home it ran great, very strong. I parked it in the garage but when I went to move it to the barn for short term storage it would not start. I removed the starter and tested it on the bench with no luck. I had the starter rebuilt and tested it on the bench with it working properly. I replaced the starter. It still will not start. I took a jumper lead and jumped power to the starter relay and the starter turns over. Next, I unplugged the key switch and when I jump power to the red/green wire (two wires on the same connector) the started turns over. I have three 420’s so I took the key switch out of one that runs and tried that, still no luck. My key switch has six connectors. Four connectors are arranged in a square block formation with a fifth one centered above the block of four like a roof on a house. The sixth one is off by itself. The bottom two connections are empty (not used). The upper left has the red/green wire. The upper right has a purple/purple wire. The center top (roof) has a single purple wire. And the sixth connector off to the outside has a red/pink wire connected to it. Can anyone tell me what these different wires are for? What circuits are made in the switch when the key is on the off/run/start positions? Where can I purchase a new “PED14” terminal block for behind the key switch? Mine does not hold the wires very well after I removed some of them. I am guessing I may have a bad safety switch somewhere. I would really appreciate any assistance you can offer!
 

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Safety switches can be tested with a VOM meter, set for lowest ohms range or continuity. There is one on the brake, there is on on the seat, and the forward/reverse level at the neutral detent.

do you have the TM for the 316/318/420 series tractors? If not PM me
 

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Hobby,

Welcome to owning a 420, one of the classic vintage Deere garden tractors.

The 420 shares the safety wiring with the 318, so many threads on this site cover how the interlock switches impact starting/cranking the engine over. Here is a wiring excerpt that shows the components in line to allow the solenoid to close and provide a high current path to the starter from the battery.
318 Starting circuit.JPG
You can see that power to pull in the solenoid passes through the key switch twice -- first through the B-A contact pair and through the 20 amp fuse on to the PTO safety switch contacts, then to the neutral switch and to the parking brake switch (if fitted, that started with 420 SN 595881) to the second pass through the key switch at contact pair S2-S1 and finally on to the solenoid winding. If any one or more of these components is open, the starter motor will not crank.

The key switch itself has terminals that are not used in this tractor model. Only the A, B, S1 and S1 terminals are used, and this illustration shows their locations and how to test a key switch:
Key switch test.jpg

Here is a fragment of the schematic that shows the wire colors as well, with some minor variations noted by serial number and model:
key wiring.jpg

Post back to this thread with any questions you have after you have absorbed this information...this forum is here to help you.

Chuck
 

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Guys, I just learned more in the last 5 minutes than I thought possible. Thank you for your quick responses and excellent information. I am working for the next 6 days but will be back on the farm after that. It will give me a little time to study before then. One more question; physically, where is the parking/neutral switch located? Under the dash? Under the battery box? Or someplace else? pretty sure I know where the other are. This is such a great web site.
 

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Chuck, Any chance that you have the other page (to the right) for the 316, 318 and 420 schematic? I am sure I will end up rewiring this tractor next winter and that would come in handy. I really appreciate the assistance you and the others provided.
 

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Hobby,

Glad to help. That wiring fragment is a composite I made for discussions just like this one, but the complete schematics and some theories of operation are in this somewhat larger excerpt. Don't let the drawing title worry you, it covers the 420 as well.
View attachment 318 Tm1590 schematics.pdf

Here is the location of the neutral switch. It is actuated directly by the ground speed lever as it rests in the STOP/neutral notch in the dashboard. Depending on the SN of your tractor you will have this style or a later plastic housing plunger switch...
318 neutral switch testing and adjustment.JPG

Chuck
 

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Discussion Starter #9
Chuck,

Thank you! I would have never looked there. I was searching down towards the bottom.

I am sitting here retracing all of my steps and I remembered that I put in a new starter relay when I replaced the starter. Sometimes I have a photographic memory and other times I cant remember anything. I am thinking I wired the relay wrong. Of course the two large positive leads go on the large posts. I only remember hooking up one red wire to one of the small posts. I bet I need a purple wire on there too. How do I tell what post gets what wire? It was -20 degrees and my heater was not keeping up, so I bet I hurried through it. What do you think? When I jump power to the red/green connector "B" the engine turns over. Shouldn't it turn when I put the power to the purple wire "S1" instead? If I am reading the schematic correctly the power comes from the battery to "B" via the relay, then out "A", goes around the horn through all the safeties and back into "S2", then out "S1" to the starter (relay then the starter). Am I on to something or was I totally asleep 34 years ago during auto electric class in high school?
 

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Hobby,

It does sound like your key switch harness wires are perhaps scrambled, so check them carefully against teh wiring diagram.

Here is the kit picture and wiring for the AM107421 Starter Improvement Kit that you may be calling a "starter relay" in your post above.
starter improvement kit photo.jpg starter improvement kit schematic.JPG

...and here are the installation instructions. In the initial post of this thread you said it ran well when you first got it from your dad -- something like the famous "ran when parked" we all hear from time to time. Have you been unable to start your 420 since you installed this kit??? Have you ever has it started from the key switch at all since you installed it???

starter improvement relay install 1.jpg starter improvement relay install 2.jpg starter improvement relay install 3.jpg starter improvement relay install 4.jpg

starter improvement relay install 5.jpg starter improvement relay install 6.jpg starter improvement relay install 7.jpg starter improvement relay install 8.jpg

If you prefer them as a PDF file, then this is the document:
View attachment Start Relay Kit M77862 instructions.pdf

Chuck
 

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Discussion Starter #11
Chuck,

That is not the starter relay I am speaking of.

Yes, It ran when parked. Then the starter went out. I replaced the starter after testing it on the bench. When I replaced the starter I also replaced the relay. Hasn't started since.

The relay looks like this.
http://shop.advanceautoparts.com/wcsstore/CVWEB/staticproductimage//421/large/5972833_cbw_s5049p_pri_larg.jpg

It is located under the battery box on the right side of the tractor next to the vent opening.

Is this not a factory item? I took the old one to the auto parts store and got an exact replacement based on the numbers stamped on it.
 

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OK, that is the separate starter solenoid as used with the Onan B-series engines. Here is the wiring diagram for it from the TM1590 service manual, which shows both the integral solenoid of the P-series and the separate parts used on the B-series. The illustration included here shows the firewall mounting of the solenoid as used on the early tractors and shows the serial number break for the 420.
solenoid terminals on B series machines.JPG separate solenoid wiring detail.jpg

As I recall, the Deere solenoid had one side of the coil tied to the mounting frame and received its ground via that path...the one you picture from the auto parts store has small terminals for both sides of the coil. Be sure that the side that does not have the purple wire is somehow returned to chassis ground or it will not operate.

One more thing to check on your older tractor -- the circuit breaker shown mounted near the solenoid has press on connections that can age and weaken over the decades due to corrosion and getting hot if poor contact pressure is causing a higher resistance. Replacing the terminals with ring type terminals and nuts on the breaker studs as used in later tractors. Also, these breakers often fail with age as well and only cost a few bucks so replacement is a good preventative measure. These are 25 amp breakers and should be available at an auto parts store and certainly from Deere (for more money of course...) :)

Since you have multiple 420 tractors do you have the TM1590 manual? All all your tractors the same vintage, or do some have the P-series engine?

Chuck
 

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Hello StanfordHobbyFarmerButCallMeEdBecauseItIsShorter.

Hello Ed. You only need for now to be concerned with component in the starting circuit, attachment one from Chuck. Next, important information is the second attachment that shows the switch connections and which terminals have power during OFF/RUN/START function. You need to get out your multimeter and since you have already confirmed there is 12V at that terminal you need to go to each component in the circuit and make sure there is power coming in and power going out. That is how I tracked down failed coil on my 216 restoration.

It is easy to replace the start relay you picture because you assume that is the problem. I have a cardboard box full of good relays I replaced because I assumed they were bad (did it on the 216 again I just finished up). Stop that. I have only once had a truly failed starter relay. It was on my 94 Ford pickup (same part).

Good luck with the fix ... Gabby

BTW ... Welcome to WFM.
 

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Discussion Starter #15
We have success! Ended up with more than one problem. My purple wire to the starter solenoid needed a new end on it. Also The connection for the 20 amp inline fuse only worked intermittently so I replaced that with a blade type fuse and holder. And finally my neutral safety switch needed an little adjustment. Many thanks to everyone who contributed to my success. I really appreciate all of the advice and especially the diagrams, they are worth their weight in gold. Once again I am mowing grass in Stanford township!! Thank you.
 

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Ed,

Excellent to hear that you got it all sorted out!!:good: Enjoy your tractor and the springtime as it unfolds...

Chuck
 
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