Scag start problem

[Proud Veteran]

Question! I have a Scag 48" Tiger Cat II with the 22hp Kawasaki engine. Key does nothing so I tried jumping straight to starter. Started right up so next I thought solenoid. I noticed in the wiring diagram that there is a diode in the wire going from the ignition to the solenoid so I ran a wire from the ignition to the + side of the solinoid. Starts just fine! Sure enough there is no continuity from the key to the solenoid so I suspect the diode is bad. I was an electronic specialist in another life so I know that a diode let's current flow one way but not in the other. My question is this, what is the risk of bypassing the diode and just running a wire from the ignition switch to the solenoid and if it will cause damage anyone know the location of this diode? Any feedback is greatly appreciated!

 

[LittleBill21]

are you sure the diode isn't across the coil terminals of the solenoid?

 

[RandyT]

There are a lot of components between the key switch and solenoid. Namely the pto switch, seat switch, parking brake switch, the brain box that controls everything to name a few.

 

[ddbackhoe]

Question! I have a Scag 48" Tiger Cat II with the 22hp Kawasaki engine. Key does nothing so I tried jumping straight to starter. Started right up so next I thought solenoid. I noticed in the wiring diagram that there is a diode in the wire going from the ignition to the solenoid so I ran a wire from the ignition to the + side of the solinoid. Starts just fine! Sure enough there is no continuity from the key to the solenoid so I suspect the diode is bad. I was an electronic specialist in another life so I know that a diode let's current flow one way but not in the other. My question is this, what is the risk of bypassing the diode and just running a wire from the ignition switch to the solenoid and if it will cause damage anyone know the location of this diode? Any feedback is greatly appreciated!

green wire and green with black stripe? Is the diode across the relay coils. It would be best to replace the diode, its job is to help keep the relay from burning out when it switches legs.

 

[LD1]

If I am looking at the same schematic as you......looks like your mower has a "module" or little brain-box thing.

Looks like that diode protects that brainbox from the voltage spike when the starter solenoid field collapses.

If thats the case....I'd either test and/or replace just that diode. Most cheap volt-meters will test diodes.

But RandyT's statement of alot of components between the key and starter.....yes and no.

Its NOT like a continuous series circuit daisy-chaining through all the safetys and if any single one is open it wont start.

All the safety switches go through that little brain-box. And if the brain-box gives the "all-clear" to start, it gives the ground for the start relay on the green and black wire. The relay then gives the start solenoid 12v on the green and white wire.

Thats my amateur diagnosis.

And as cheap as manufactures are anymore....I would find it unlikely for them to put something there (diode) that wasnt actually needed.

 

[WinterDeere]

Classic "flyback diode", essentially a surge suppressor, as LD1 suggests. If bad, just replace with similar type and size. DigiKey is your friend, they do small credit card orders for personal stuff. Heck, you can probably get them on Amazon now, too.

Where's the schematic you guys are looking at?

<-- MSEE

 

[EddieWalker]

I bought my Scag Wildcat new from the dealer back in 2012 with the 26 HP Kawasaki engine. For the first couple of years, it was flawless. Then I started having issues getting it to start. It was always a safety switch that needed replacing. I had to check all of them, and then bypass it, or replace it. This became a common issue, but then the PTO switch quit working, and then I had to replace the generator, twice. I also replace the PTO switch 3 times.

When it was about 5 years old, I never expected it to start. There was always an issue that I had to fix, bypass, or replace. It might work the next week, or even a couple weeks in a row, but never a full month. Then it started blowing the 20 amp fuses. It would run for an hour, maybe two hours, or maybe half an hour, then the PTO would stop working and I would replace the fuse. I could go through 3 or 4 fuses in a day.

Three years ago I had enough. I pulled every wire out of it and I bought a new aftermarket key switch, and a heavy duty toggle switch for the PTO. I ran the bare minimum for wiring. Just what I needed to get it to start, turn off, charge the battery, and run the mower blades. Since then, it's worked perfectly every time I use it!!!!!

 

[WinterDeere]

Three years ago I had enough. I pulled every wire out of it and... Since then, it's worked perfectly every time I use it!!!!!

Was Scag ever owned by Lucas Electronics? Sounds like a 1970's British sports car, in terms of electrical system reliability.

 

[LD1]

Classic "flyback diode", essentially a surge suppressor, as LD1 suggests. If bad, just replace with similar type and size. DigiKey is your friend, they do small credit card orders for personal stuff. Heck, you can probably get them on Amazon now, too.

Where's the schematic you guys are looking at?

<-- MSEE

 

[EddieWalker]

I've been sharing my issues with my Scag mower for awhile now, and from what I've heard from others with different brands of zero turns, it sounds like everyone has issues with their electrical systems.

 

[LD1]

I've been sharing my issues with my Scag mower for awhile now, and from what I've heard from others with different brands of zero turns, it sounds like everyone has issues with their electrical systems.

Yup....it's not just scag.

The wildcat is a commercial grade mower (I have one too but with the Kohler 27 or 28hp).

But comparing exmark, toro, scag, hustler, etc.....they are pretty much all identical except paint color.

They use the same generic key switches, same safeties, pto switch, etc etc.

Engine options, hydraulics, etc....pretty much all the same.

Deck designs (spindles and airflow) are really the only differences other than paint color.

I do work on a lot of different mowers for my buddies landscape company. My wildcat is actually one of their older mowers I bought. But they have scag walk behind, scag v-rides, toro 6000-series, toro grandstands, exmark walk behind, exmark riders, throw in an odd JD z700 series and a older Kubota.

You'd be surprised just how many of these smaller components are interchangeable. Pretty much all the switches, and even pto clutches for the most part.

On my personal scag.....I bypassed ALL the safeties. Which is the seat switch, park brake, and both levers "home" position.

Means I can get off the mower to move a stick without it dying because I forgot something or didn't get one of the levers home.

The ONLY issues I have is when a fuse blows. It's usually for the charge. No rhyme or reason to why it blows. Maybe once a year. But I don't notice it til the mower either quits (battery runs dead) while mowing and it won't restart....or if I am lucky to finish that mowing but have a dead battery next time I try and mow.

 

[WinterDeere]

I've been sharing my issues with my Scag mower for awhile now, and from what I've heard from others with different brands of zero turns, it sounds like everyone has issues with their electrical systems.

The only issue I've ever had with my 2007 Deere Z757 ZTrak is a seat switch delay module relay that went bad ca.2020. It was intermittent, which means I had to let it "fail" two or three times before confirming the issue, but the repair was ultimately as easy as unplugging the old one and plugging in a new one.

I also had two PTO clutch failures, before noticing a small but hidden hole in the muffler, that was directing a jet of hot air right at the clutch coil, ultimately causing them to overheat and fail. I can't blame the electronics for that, but I do wish they had done a better job of welding that muffler, as the hole was the result of a failed heat shield weld.

 

[WinterDeere]

[wiring diagram]

Thanks. Unfortunately, it's hard for someone not already familiar with these mowers to get much from that wiring diagram, if you don't already know the components at each end. I have no idea what's on the other end of "module plug", and that would be required to figure out the pin-out of "relay", and thus what that diode at the engine adapter harness plug is actually doing.

The reversed 600V/2A diode at the clutch is a classic example of a flyback diode, reversed biased and there just to absorb a transient when the clutch is disengaged. But I assume the one in question is the one at the engine adapter harness, and its function is less obvious from the wiring diagram alone. I'd guess LD1 is right though, it's for protection of the engine module electronics.

 

[LD1]

Thanks. Unfortunately, it's hard for someone not already familiar with these mowers to get much from that wiring diagram, if you don't already know the components at each end. I have no idea what's on the other end of "module plug", and that would be required to figure out the pin-out of "relay", and thus what that diode at the engine adapter harness plug is actually doing.

The reversed 600V/2A diode at the clutch is a classic example of a flyback diode, reversed biased and there just to absorb a transient when the clutch is disengaged. But I assume the one in question is the one at the engine adapter harness, and its function is less obvious from the wiring diagram alone. I'd guess LD1 is right though, it's for protection of the engine module electronics.

The other side of the "module" plug is just that....and electronic module.

Electronic Module

www.scagparts.net

However, it has nothing to do with the engine, and isnt an "engine" module at all. Rather it is a safety interlock module. All the safety circuits go through it (instead of daisy-chain fashion). And if all safety's are in their proper position, it will give the ground signal to the start-relay.

IT also has some kind of "logic" to it. Meaning if blades are ON and seat becomes unoccupied, it kills the mower and deck. OR if park brake is set, but handles come off home position.....also kills the engine. Or as long as park brake is set, handles in "home" and PTO is off.....it ignores the seat switch (meaning you can get off without killing engine.

Again, its got a "logic" base to it. And being that its a printed circuit board....my best guess is the diode is preventing a voltage spike on that board when the starter solenoid is de-energized