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Discussion Starter · #1 · (Edited)
Hello, I am new to the forum, but it looks like there are quite a number of knowledgeable, helpful people here. The internet is such a great place to meet, I wish it had been around 60 years ago. Amazing technology! Anyway, to my problem: the problems started when I decided to replace a defective ignition switch on my 318 loader tractor. I got an aftermarket switch (Indak brand) off ebay. I had to take the seat off to enlarge the dash hole for the new switch, so I decided to replace the worn out seat as well. Had to wait to get the seat, so I took the seat mounts off to clean up and repaint. Also,decided to incorporate ROP when I put the seat mounts back. That thing gets a little scary on a 20% grade with a bucket of gravel. Went to start up a week after switch install and blew the main 20amp fuse...three times. Obviously, a problem. Long story shortened, the aftermarket switch is shorted to ground when in the run or start positions. Installed an OEM switch and it stopped blowing fuses.However, now the battery light just flashes when the key is turnedon, and the ignition is dead (oil light stays on.) I cleaned up a whole lot of corroded terminals, and when I initially put it back together, I was able to start up and run normally.....once. Turned it off and now short flash of battery light. I have bypassed (to check) the interlock switches, they all check out. Cleaned more corroded connections. PO had jumpered the seat switch, and, somewhere along the way, somebody put a starter improvement kit on it. Since the battery light flashes for a second, I am thinking the Time Delay Control Module or a broken wire somewhere in an interlock circuit. Problem is, it has run fine for years, so broken wire is not too likely. All I messed with was behind the dash to replace the ignition switch and the seat mount(including bypassed seat switch wire). Could the short have caused avoltage spike that fried some electronics? The ignition circuit comes up, but only momentarily. Any ideas? I have wiggled connections while the ignition is on....not even a flutter. Thanks for your anticipated input.
 

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Could the wrong switch have fired your electronics? Yes. When a new one from the dealer is only $20 its going to be an expensive lesson. Where to start? You need a wiring diagram for your tractor and a volt ohm meter. Look for burnt looking and smelling stuff.
 

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The ignition switch that you got off ebay must not have been correct for your tractor. These switches have different terminals and contact connections inside the switch for different applications. I have bought several switches off ebay and not had a problem. I didn't have to change the hole for the switch on any of them. You have to have a wiring diagram for your tractor. The service manual shows two different diagrams depending on if the tractor has a rear PTO. I always disconnect the negative terminal of the battery when I am working on the wiring. Did you check the 3 amp fuse? Do you have a P218 or B43G Onan engine?
 

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Discussion Starter · #4 ·
Thanks for the input, I have a wiring diagram, but was looking for a place to start with the multimeter, based on others experience. Actually, thinking about buying a used time delay module for test purposes since I have two 318s and these boxes seem to cause frequent problems. The pin configuration was the correct one on the aftermarket switch, but no matter its application, there shouldn't be sparks from the switch case to ground. That is a direct short, and I can't think of any application where that would be an intentional situation. That said, I have had past issues with the local JD dealer, so tend to shy away from them. Still "lesson learned" is applicable, but I knew the risks. "Sometimes, you get the bear, and sometimes the bear gets you." OUCH! Think I will go ahead and try to buy a used module just to keep for diagnostic purposes. Again, thanks for the input! I appreciate you taking your time to respond.
 

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Seriously use your nose and eyes to check first. Saves a lot of time when dealing with "I let the smoke out" issues. Some of the advertisers on here deal in discount priced genuine JD parts.
 

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Discussion Starter · #6 ·
Just a quick follow-up: The defective ignition switch did do some damage to the time delay control module (TDCM). Replacement solved the problem. There was no evidence of a problem on the PCB. Everything looked fine. I have not gotten into it yet, but I suspect that it fried one of the relays on the board. The symptoms were: when the key was turned on, the oil pressure light came on and the battery light flickered and went out. The tractor would not turn over. The start circuit was dead. There was 12 volts at pin 1 and also at pin 3 of the TDCM when the switch was on. Hope this helps.
 

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If you can get the relay covers off you will see which one it is. Some covers pry off pretty easy, some do not. You can replace those relays, needs to be un-soldered and the new one soldered in. Solder wick is your friend. Done it lots of times, not on a TCM but you do need a low wattage 25 watt or so iron and some really fine solder, 40/60.
 

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Arthur,

The TDCM is not in the starter cranking circuit as shown below, so the starter motor should at least "turn over" the engine when the key is turned to START, even if the TDCM were completely unplugged... If by "not turn over" you mean instead the the engine did not fire...then MAYBE the TDCM is involved as its function is to inhibit ignition when certain conditions are not met. Here are two wiring excerpts that help this discussion:




In the first diagram that describes the engine starting (cranking) wiring the TDCM is not a factor at all...the engine should spin when the key is turned to start -- if not the issues are in the brake, neutral and PTO switches or the 20 amp fuse. Older tractors do not have the brake switch fitted.

In the lower diagram, you can see that the power to the ignition coil and the hour meter is supplied from the TDCM when the key is on IF AND ONLY IF the operator is in the seat and the seat switch circuitry is working -- causing voltage to be present at pin 9of the TDCM; OR the tractor is in park with the ground speed lever in neutral and all PTO switches are off -- causing voltage to be present at pin 7 of the TDCM.

When either or both of pins 7 or 9 have voltage and there is still no power at pin 2, then there may not be power INTO the TDCM at pin 3 from the 20 amp fuse or perhaps there is a bad ground at pin 10. If all the EXTERNAL conditions appropriate for the TDCM are satisfied and you still have no joy at pin 2...then it may be an internal component or trace inside the TDCM itself.

The schematic of the inside of the TDCM shown in the Deere wiring diagrams is very simplified over the actual assembly, but does somewhat represent the functioning... If in attempting to install an non-stock ignition switch in your tractor you had caused power to go where it should not, or to short a functional circuit in some way -- then damage could have been sustained by the TDCM. Some things to look for are:
1. open diodes -- these are not rated for currents higher than the normal operating ones and will fail open if stressed. Sometimes the glass package will crack as well...
2. burned or open traces -- again the circuit traces are printed to handle the 'normal' conditions and may fry if stressed by unacceptable cross connections.
3. failed or burned relay contacts -- high currents here can burn the metal surfaces and cause them to not conduct as the should when they should.
4. open relay coil winding -- not as common, but possible. Replacing the entire relay would be needed in that case.
5. fried semiconductors -- transistors C and D in tghe above diagram and lots of otehr components not shown here are also susceptible to damage by stray high current voltage paths and shorting of their connections...you will likely not find all of these if they exist and may not be able to replace them either if your skills are predominantly mechanical.

Please note that sometimes the symptoms/issues attributed to the TDCM are really just poor connections in the connectors at X22 and X23, so changing it out for another one will appear to cure the issues. You may find that placing the original one back in the tractor without doing anything to it in the way of repair will also yield a fully functioning tractor...

In any event, let us know what you find.

Chuck
 

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