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John Deere SST18 charging light issue

14 years ago

I have been experiencing an issue with the battery charge light on my 2001 vintage SST18. The light comes on intermittently when the machine is running. The battery appears to be fully charged and the machine starts with no indication of a low battery.

The service manual states that the first thing to check is the voltage at the battery. I have done this and it is about 13.8 V. This is in spec and is enough to charge the battery. I have run the machine with the volt meter attached and notice no difference when the light is on or off.

Recently the light stays on more than it is off. I intentionally partially discharged the battery after which I noticed that the charge light stayed off for a while.

So, I figured that the issue might be the OLD original battery not accepting the charge. I ran the machine and, while the charge light was on, jumpered it to the battery on my JD314. The light stayed on and the voltage only dropped about 0.1 V.

Any ideas?

TIA,

Ken

p.s. I wish this thing qualified as a Federal clunker. I would trade it in a minute :-)

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Comments (5)

bobodu
14 years ago
Sounds like either a short,corrosion or a loose wire.
mownie
14 years ago
Without the benefit of a wiring diagram, I suggest you look around behind the instrument panel for any relays that may be associated with the charge indicator light. A way to test whether a relay had any control over the charge indicator light would be to turn on the key switch, but don't start the engine. Unplug any relay and see if that "puts out" the indicator light. If you locate a relay that "puts the light out", check all the blades and terminals of the relay for being loose or corroded. Look at the body of the relay that surrounds all the terminal blades, you might find a crack or a green streak indicating the the relay may have internal faults.
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taylorkh
Original Author
14 years ago
Thanks for the replies. Having the "benefit" of the wiring diagram I determined that the charge light connects to one lead coming from the regulator/rectifier and to ground. Quite simple.

On the other hand the manual states "The voltage sensing circuit used by the regulator/rectifier to adjust its output receives power from the orange wire..." (which runs through hell and Hoboken) "...and on to the battery positive terminal." "If the system voltage drops below an acceptable level (approximately 12 volts) the discharge light receives voltage..." (from the wire I referenced above).

So I started the machine, the light came on and I measured the voltage at the orange wire going into the regulator/rectifier - 14.4 Volts. This being more than "approximately 12 volts" I would expect the light to be extinguished. By time I reconnected to measure the voltage at the battery + terminal the light had gone out. 14.3 volts at the terminal and the same at the wire going to the regulator/rectifier.

Sounds like the regulator/rectifier is bad(?)

I guess I could splice into the orange wire at the regulator and monitor the voltage during operation and see if there is any correlation with the light.
taylorkh
Original Author
14 years ago
Went to the local JD dealer this afternoon.

1 - A new regulator is the better part of $100.
2 - They have no way to test the suspect one.
3 - The service manager said if it is charging to 14 volts, don't worry about the light.

So, I pulled the bulb from the charge light. If the machine fails to start some day - I have a plug in charger. If that doesn't work there is a scrap yard down the road for the SST and a real ZTR for my lawn.
bobodu
14 years ago
14 volts is actually closer to "acceptable" than 12.

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