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Scag STT61-25ch Wiring Issue

#1

J

jd12

I have a Scag STT61-25ch mower with a replaced Kawasaki motor. The serial number on the chassis indicates that the original motor was a Kohler. The new used Kawasaki motor I installed starts fine with the key but will not shut off with the key. Therefor it has a wiring harness for the previous Kohler motor. There is an aftermarket switch on the side of the console box that might have been used in the past as a kill switch. Since I purchased the Scag with the blown Kawasaki engine and have no history on the machine, it’s hard to say what happened to the original kill switch. I have reviewed the wiring diagram for the mower to help identify which wire is responsible for shutting off the engine when I turn off the key, to no avail.

Does anyone have any ideas which wire can kill the motor on a Kohler harness for a Kawasaki motor?



Thanks in advance.


#2

B

bertsmobile1

We can not check which particular wiring harness you have unless you post your serial number because that is how Scag lists them.
Some Scags kill the engine by the key switch connecting the G ( ground ) wire which is black with the magneto wire , possibly white and marked with M on the back of the switch.
Others have a relay and the engine is turned off by the power being cut to the relay which makes a ground contact to the magneto .

Not depicted on the diagram is the carb solenoid which should also kill the engine

So take the blower housing off the engine and see where the wire that connects both coils goes to on the engine plug.
Confirm continuity on this wire

Then check that the opposite side on the mower plug goes from ground ( engine off ) to open engine running .
If not check that colour wire at the plug behind the key switch and while it is out check that the black wire is in fact a good ground .
Also check that the key connects the ground & magneto wires when the key is off

Let us know what you find.


#3

StarTech

StarTech

There was only three serial number breaks for the SST61A-25CH mower. All three used the same wiring setup. The kill wire at the engine connector is the white wire. There will two white wires at the ignition switch on the same terminal. One goes to the engine and the other to the safety module (which its kill for the engine). Here is the pin out for the original ignition switch. The unlabeled terminal usually has separate wire attached. Scag 48798 (Stens 430-950 Rotary 7804).
1687086206381.png
Can't help if you have an unknown ignition switch.


#4

J

jd12

bertsmobile1 said:
We can not check which particular wiring harness you have unless you post your serial number because that is how Scag lists them.
Some Scags kill the engine by the key switch connecting the G ( ground ) wire which is black with the magneto wire , possibly white and marked with M on the back of the switch.
Others have a relay and the engine is turned off by the power being cut to the relay which makes a ground contact to the magneto .

Not depicted on the diagram is the carb solenoid which should also kill the engine

So take the blower housing off the engine and see where the wire that connects both coils goes to on the engine plug.
Confirm continuity on this wire

Then check that the opposite side on the mower plug goes from ground ( engine off ) to open engine running .
If not check that colour wire at the plug behind the key switch and while it is out check that the black wire is in fact a good ground .
Also check that the key connects the ground & magneto wires when the key is off

Let us know what you find.
Click to expand...
Thanks so much for the ideas! I will check your ideas and get back to you.



Attached are the serial number. One item is the third picture shows the mis match of the computer hookup to the Kohler harness. I removed the clear connector and stabbed it directly into the black block. My assumption is that this might work since the pin and color alignments looked the same.

Attachments









#5

J

jd12

StarTech said:
There was only three serial number breaks for the SST61A-25CH mower. All three used the same wiring setup. The kill wire at the engine connector is the white wire. There will two white wires at the ignition switch on the same terminal. One goes to the engine and the other to the safety module (which its kill for the engine). Here is the pin out for the original ignition switch. The unlabeled terminal usually has separate wire attached. Scag 48798 (Stens 430-950 Rotary 7804).
View attachment 65217
Can't help if you have an unknown ignition switch.
Click to expand...
My ignition switch looks like your diagram but no white wires. The machine did not have a wiring harness when I purchased it, so I purchased the one that match the serial number of the unit(Kohler). In the attached photo you can see there is no white wires on the new harness at the ignition switch. Which lug in your diagram should be the white wires?

Thank you for your help.

Attachments





#6

B

bertsmobile1

Take the switch out
Check that the black wire is actually Ground
Then look for a terminal that makes continuity with the G terminal when the key is OFF and no contact when the key is on
That is the magneto kill wire if the switch is the correct one .
IF you are lucky there will be tiny letters cast into the back of the plug or stamped into the pins
M = Magneto
G = Ground
B = Battery
S = Start


#7

J

jd12

So my G lug has black wires and my M lug has no wires. This is a brand new harness, could this be a system like you talked earler about using a relay to kill the motor?


#8

StarTech

StarTech

What is the harness PN? I showing you should have the 482656 harness which images of the ignition switch shows the white wire.
1687265094031.png


#9

J

jd12

Here is the line item from the invoice. This was ordered on powermowersales.com, they claimed this is the correct harness for my serial number for a Kohler motor. I did install a Kawasaki motor that replaced the Kawasaki motor when I purchased the machine. But somewhere along the line someone fitted a Kawasaki in place of the Kohler, which I did not know when I ordered the harness.

481752 Scag 481752 WIRE HARNESS, STT-KA
$291.82 x 1
$291.82​


#10

StarTech

StarTech

Now that changes the whole ball game.
1687287880326.png
1687287918684.png
Coming from the module plug (terminal F) would be the kill wire for the engine. for the ignition to operate as the kill switch then a wire would need to be added the M terminal (terminal B in the engine diagram) to the control module terminal F.

Now does assume you have the water cooled FD engine series. Other series may have engine wiring setup but you have not told us exactly what you are dealing with.


#11

J

jd12

Here is the line item from the invoice. This was ordered on powermowersales.com, they claimed this is the correct harness for my serial number for a Kohler motor. I did install a Kawasaki motor that replaced the Kawasaki motor when I purchased the machine. But somewhere along the line someone fitted a Kawasaki in place of the Kohler, which I did not know

481752 Scag 481752 WIRE HARNESS, STT-KA
$291.82 x 1
$291.82​
StarTech said:
Now that changes the whole ball game.
View attachment 65299
View attachment 65300
Coming from the module plug (terminal F) would be the kill wire for the engine. for the ignition to operate as the kill switch then a wire would need to be added the M terminal (terminal B in the engine diagram) to the control module terminal F.

Now does assume you have the water cooled FD engine series. Other series may have engine wiring setup but you have not told us exactly what you are dealing with.
Click to expand...
Thanks so much! It sounds like I have the wrong harness and I need to improvise it to make it work.


#12

StarTech

StarTech

jd12 said:
Thanks so much! It sounds like I have the wrong harness and I need to improvise it to make it work.
Click to expand...
That where most of us have to made modifications base on our knowledge of things. Retrofits are where we have to do these mods.


#13

J

jd12

jd12 said:
Here is the line item from the invoice. This was ordered on powermowersales.com, they claimed this is the correct harness for my serial number for a Kohler motor. I did install a Kawasaki motor that replaced the Kawasaki motor when I purchased the machine. But somewhere along the line someone fitted a Kawasaki in place of the Kohler, which I did not know

481752 Scag 481752 WIRE HARNESS, STT-KA
$291.82 x 1
$291.82​

Thanks so much! It sounds like I have the wrong harness and I need to improvise it to make it work.
Click to expand...
That worked! It’s amazing how one simple wire can provide so much joy.

Thanks so much for your help and assistance.

It means a lot!


#14

J

Jcota SCAG

Question Folks, I have a similar model STT61A-25CH. Basically, I was mowing, and the old girl shut off and wouldn't crank anymore. Found a switch stuck closed on the left handle which I replaced but to no avail I was losing power when it would sit, and it looks like the wiring has been messed with connectors here and there, so I was thinking of just replacing the entire wiring harness. Will the harness mentioned above work for me?


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