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Old 07-20-2011, 07:50 PM   #1
FLScott
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Default LT155 with Safty Switch Problems

I took my LT155 out of the garage last weekend and it started fine. A few minutes into mowing, it just quit. Pressed the brake pedal in and it restarted. Let the brake out and it quit.

I disabled all the safety switches (seat, brake, pto). Started fine and runs great. All functions work, just no safety systems work. I checked all the switches with a VOM and they seem to work fine. There are two identical relays mounted under the battery. I switched plugs on the relays with all safety switches connected and I still have the stalling problem as soon as I release the brake.

There was a post with a similar problem on this forum a couple of years ago, but the preson that posted the problem never said what they did the fix the problem.

I can easily replace all three switches, but what other parts are associated with the safety cut-out system (relays, diode, ignition switch, fusable links, etc)?
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Old 07-20-2011, 09:55 PM   #2
andythedrew
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Default Re: LT155 with Safty Switch Problems

Did you disable them all at once or did you disable one at a time to isolate the problem? Chance all those items failed at once are slim. Sounds like your seat switch but could be wrong. Might be a short.

edit-- sorry should have read more closely I see you checked them..
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Old 07-20-2011, 11:51 PM   #3
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Default Re: LT155 with Safty Switch Problems

I agree with andy...

plug them all back in, and be sure the problem still exists.

now unplug one, test, if that is not it, reconnect that one and move on to the next one... you should find the bad switch pretty quick...



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Old 07-21-2011, 12:03 AM   #4
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Default Re: LT155 with Safty Switch Problems

Seat switch/wiring. AFAIK that's the only one that will kill the engine as the brake is released.
A further check - with the brake still on, engage the PTO. What happens?

It is possible that the linkage is rubbing on the mag kill wire, grounding it.
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Old 07-21-2011, 05:49 PM   #5
FLScott
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Default Re: LT155 with Safty Switch Problems

Regarding the safety switches, I tested the seat switch no continuity when open and continuity when closed (seated on tractor).

Then I bypassed the seat switch by using a jumper in the plug simulating someone on the seat. The engine started and when the brake pedal was released the engine stopped. This should clear the seat switch.

Next the the brake switch was disconnected. I had to jumper the black wired to start (the seat switch remained with the jumper in place). The relay under the battery shelf clicked when I jumpered the black wires. After the engine started, I removed the jumper across the black wires on the brake switch and the engine continued to run. When I engaged the PTO, the engine quit.

I restarted the engine and applied the jumper across the white wires on the brake switch and the engine quit.

Next I then disconnected the PTO switch and started the engine. At this point all functions of the tractor worked (forward/reverse and PTO).

I have the wiring diagram for the LT133/155 (3-amp) and it identifies the PTO Switch, Brake Switch and seat switch which I have found. The diagram also shows an S4 RIS switch and an S5 RIO switch, which I cannot find these switches. The diagram also identifies four relays (K2 Seat Relay, K3 RIO Latch Relay, K4 Out of Seat Relay and a K5 Shunt Relay). I found the two relays under and in front of the battery shelf. I believe that I have found the K2 and K4 Relays, but cannot find the K3 and K5 relays. There are not many places to hide the switches and relays. Maybe the wiring diagram is from a newer model of the LT133/155 models? Mine is a 1994 or earlier model.

The brake switch and PTO switch are identical. The two relays I found are also identical, but no other switches or relays under the hood or dash area. The deck was removed and I looked on the back by the transmission the area around the deck for more relays and switches, but no luck.

I checked as much of the wiring as possible, but did not see any worn or pinched wires.

"It is possible that the linkage is rubbing on the mag kill wire, grounding it."

What does the mag kill wire look like and what does it connect together?

Thanks!
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Old 07-21-2011, 06:23 PM   #6
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Default Re: LT155 with Safty Switch Problems

The mag kill wire will come from under the engine tin and go to the ignition switch. When you shut the ignition off, it grounds the magneto and kills the engine. So, anything that grounds that wire will kill the engine. This is assuming, of course, that you do have a magneto ignition.
It is a long shot, but still possible. I think the wires are generally black, but there's no guarantee on that.
Is there somewhere we can look at the wiring diagram? That might help us to help you.
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Old 07-21-2011, 07:42 PM   #7
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Default Re: LT155 with Safty Switch Problems

1997 was the first year of LT's.

Do you have a yellow RIO switch on the dash? If not, you have a non-RIO tractor.
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Old 07-21-2011, 07:46 PM   #8
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Default Re: LT155 with Safty Switch Problems

I think I found the mag wire the other day when I was looking for worn wires. It comes out and is encased in a an insulated sock for several inches. It does go into the general harness. According to the wiring diagram I have is is white. It goes from the magneto to the brake switch and interconnects to the brake switch. Parts not too expensive, but some out of stock. I may just change out a couple off parts a week until the problem is resolved. I just don't like running without the safety system in place. In the mean time, I will give the wired a good look over this weekend.
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Old 07-21-2011, 08:45 PM   #9
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Default Re: LT155 with Safty Switch Problems

You could use a multimeter to see if the mag wire is grounded when it shouldn't be. You could then make checks to see what is grounding it. No sense throwing parts and money at it if you don't need to. The checks could be done with the engine not running, but the key on, etc.
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Old 07-22-2011, 08:43 AM   #10
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Default Re: LT155 with Safty Switch Problems

"I just don't like running without the safety system in place." Glad to hear that.
Did you answer if you have a RIO switch on the dash? Bad switch there? Mine dies if I try to backup without hitting the RIO. Just typing out loud.
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Old 07-22-2011, 03:20 PM   #11
FLScott
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Default Re: LT155 with Safty Switch Problems

What does a RIO switch do? I see on the new models you have to push a button to go in reverse. If that is a RIO switch or it is part of that system, I do not have one. Reverse is just a press of the reverse pedal, no buttons to push or levers to pull. My lawn tractor was purchased sometime in 1997 or 1998. I thought I had originally purchased in the early 1990's, but manual was printed in 1997.

To date, I have only found two relays mounted just below the battery shelf, just behind the starter solenoid and three switches (seat, brake and pto). Then the ignition switch on the dash. There is also a diode on the harness, as well as several fusable links.
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Old 07-22-2011, 03:36 PM   #12
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Default Re: LT155 with Safty Switch Problems

Here's a wild shot...


Check the brake pedals and linkage.. any wires rubbing/moving along those move-able parts?

I wonder if a wire got wore through...
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Old 07-24-2011, 07:34 PM   #13
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Default Problem solved

Actually, I found that I had two problems. First, the chassis ground had become loose and finally pulled out of the eyelet. Second, I had a short in one of the battery cells.

I reinstalled and reconnected all the switches. I found the loose ground and fixed that, but since I had the battery out, I jumped the tractor from a spare battery (I had known that the old battery was going bad, since I had it for more than a month). Started up, left pressure off the foot off brake and it ran fine, engaged PTO and it worked fine. I replaced the old battery and it started, released the brake and stalled. Removed the battery and jumped again, disconnected the battery and it kept in running. Released the brake and it kept running, PTO worked also. Therefore, the battery was the second problem. Installed a new battery and all works well.
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Old 07-24-2011, 08:08 PM   #14
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Default Re: LT155 with Safty Switch Problems

Sounds like the bad battery was not engaging one of the relays. Since that is a ground-based system (the safety systems simply ground the coil) battery voltage shouldn't matter - unless it opens/closes a relay.

Glad you got it going, and thanks for the follow-up!
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