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Discussion Starter · #1 ·
My 1988 420, that I have been mowing with this summer, The battery light now stays lite. So far everything that I have tested shows its the Time Delay Module is bad. Has anybody removed the module and rewired their tractor with out using it?
 

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Before you go down that path, can you tell us more about your tractor.
1. Is your battery being charged sufficiently as the engine runs?
2. often that light comes on if the 3A fuse is blown or making a bad connection. That fuse can blow if there is a short to ground in the seat safety switch wiring but if it blows, the engine most likely will die if you move the hydro lever out of neutral. By chance is your seat safety switch non-functioning? Has your neutral safety switch been removed and jumped across?
 

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Heres the circuit description.

CHARGING CIRUIT OPERATION
The function of the charging circuit is to keep the
battery properly charged by supplying approximately
13.6—14.7 VDC to the battery while the engine is
operating.
The charging system is a permanent magnet and
stator type. The magnets are located in the flywheel,
which rotates around the stationary stator (G2)
windings. Current output is controlled by voltage
regulator/rectifier (N1), mounted separately from the
stator. Battery discharge lamp (P4) warns the
operator when battery discharge lamp control (A)
senses low battery voltage. The battery discharge
lamp and lamp control DO NOT monitor current
output from the stator.
As the flywheel turns, the permanent magnets induce
alternating current (AC) in the stator windings. The
alternating current flows to the voltage
regulator/rectifier. The rectifier portion of the voltage
regulator/rectifier converts the alternating current to
direct current (DC). The regulator portion stabilizes
the direct current and increases or decreases current
flow as required by the battery.
Battery discharge lamp control (A) senses battery
voltage present at fuse (F2). If the lamp control
senses low voltage (less than 12.3 volts), it will
provide a path to ground for battery discharge lamp
(P4). Since battery voltage is always available at the
discharge lamp when the key switch is in the RUN or
START position, the ground path provided by the
lamp control will allow battery current from fuse (F1)
to flow through the battery discharge lamp to ground,
lighting the discharge lamp. The lamp will stay on
until battery voltage increases to 12.7 volts. At this
point, the battery discharge lamp control will break
the path to ground, turning the battery discharge lamp
off.
Fuses (F1 and F2) protect the battery discharge lamp
and lamp control circuit from excessive current.
NOTE: (*) For machines (S.N. —475000), a light
green wire is used instead of the 210 red wire
used on later machines. The green wire
connects to terminal “B” of key switch (S1),
instead of connecting to circuit breaker (F3).
NOTE: 1. The illustration shows ground circuit for
machines (S.N. 475001— ).
For machines (S.N. —475000), the blk wire
from the TDC module 2-pin connector
terminates (grounds) at the right side of the
pedestal panel.
MX,159024020,7 -19-16MAY95
Component Location and Operation/Theory of Operation
TM1590 (17MAY95) 240-15-8 316, 318 & 420 Lawn and Garden Tractors
020895
 

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Heres the wiring.

 

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Discussion Starter · #5 · (Edited)
Before you go down that path, can you tell us more about your tractor.
1. Is your battery being charged sufficiently as the engine runs?
2. often that light comes on if the 3A fuse is blown or making a bad connection. That fuse can blow if there is a short to ground in the seat safety switch wiring but if it blows, the engine most likely will die if you move the hydro lever out of neutral. By chance is your seat safety switch non-functioning? Has your neutral safety switch been removed and jumped across?
Mike, I will check the 3 amp fuse tonight again. Last Monday I mowed with it, I shut it down while I did a couple things. When I started up the light was on. I did check a few things with the wiring. Yesterday, I checked the battery voltage, it was at 12.4. After starting it up, it read 13.6. I mowed with it for about 45 minutes, shut it off and checked the battery. It showed 13.4 volts and I had no issues with the PTO clutch working. To me, this is telling me that the charging system is working correctly. Before I do any changing, I will put my deck on my other 420 so I can do more checking of the wiring.
 

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Sounds like wiring problem either ground (via TDCM) or power from supply (head light switch). I'm thinking dirty, corroded connection in the Molex plug(s).
 

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Mike, I will check the 3 amp fuse tonight again. Last Monday I mowed with it, I shut it down while I did a couple things. When I started up the light was on. I did check a few things with the wiring. Yesterday, I checked the battery voltage, it was at 12.4. After starting it up, it read 13.6. I mowed with it for about 45 minutes, shut it off and checked the battery. It showed 13.4 volts and I had no issues with the PTO clutch working. To me, this is telling me that the charging system is working correctly. Before I do any changing, I will put my deck on my other 420 so I can do more checking of the wiring.
It does sound like your charging system is working as it should. A bad ground connection could be your culprit or a bad fuse holder.

If your tractor has glass fuses instead of the spade type, the fuse holders are known to degrade over time. Even if the fuse is good, it may not be making contact in the fuse holder. Check it over carefully.

To give your TDCM a quick check:
Drive your tractor to an open area and shut it off. With no one around you (in case the tractor starts and wants to move forward), move the hydro lever slightly FORWARD out of neutral and try to start the engine. If the starter does not engage, your neutral safety switch and TDCM are operating as they should. If it starts, check your neutral safety switch and brake safety switch wiring if your tractor has a brake switch.

With the tractor parked and running with you on the seat, switch on the PTO. Carefully lift up off the seat just a little to allow the seat switch to open and see if the pto shuts off. If the PTO shuts off, that part of the TDCM is doing its job. If the PTO does not shut off, your seat switch wiring could be jumped.
 

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Skwirl, link to pic is broken, did you drop or attach it?
I'm not sure, lol. Not very puter literate.
Hopefully my smartphone will cooperate.
I'll try again.
Well, I cant figure out how to get the wiring diagram to post.
But, its page 240 15 9 in the manuel.

Hopefully Chuck will see this and add the wiring info.
 

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Now I remembered what I do for this, screenshot.
268674


That should do it.
Theres more than 1 way to skin a cat.
 

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he-he, Not chuck, but here's the complete wiring schematic:
268675

Bob
 
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Show off, lol.
 
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Discussion Starter · #13 ·
Well................I didn't have much time to work on the 420 last night. But what time I did, I checked the 3amp fuse again. It looked good and checked out okay. So I said "What the Heck".....So I installed a new 3amp fuse in the holder.....After running the tractor for about 5 minutes, the light works properly. I will keep my eye on it when I run it next time.

Thanks!!!
 

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Glad you found a problem. If that fuse was blown or not making contact in the holder and you were still able to drive the tractor, chances are your seat switch or neutral safety switch (or both) have been jumped across and the safety features have been defeated. If you purchased the tractor that way and do not intend for the safety features to be defeated, we can help you get them back in working order.
 

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Pick up a spray can of contact cleaner. It helps remove any corrosion.
 
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