Engine How does my solenoid work? Unable to start.

[John Ambrosia]

I have a Scag Turf Tiger, model # STT61V-29DFI-SS and I have been having starting problems with it. I thought I had traced the problem to the starter solenoid and replaced it but was both disappointed and a bit demoralized when it still wouldn't start. I have a new 12 volt battery which is delivering 12+ volts so I'm comfortable that is OK. If I bypass the starter solenoid, and connect the battery positive to the starter, the engine will crank. One very basic thing that I don't understand is how this particular solenoid works. It has three terminals. Two are heavy, bolt secured terminals. The third is a smaller, flat, fin or blade type terminal. The connections are as follows: The battery positive cable and a smaller gauge red wire are both connected to one large terminal. The positive lead to the starter is connected to the other large terminal. A small gauge green wire, which I assume is the ground wire is connected to the small terminal. What I don't understand is this:It seems, from the wiring set-up I have described, that the solenoid is always being energized, which is obviously not the case, I think. I expect that the small gauge red wire somehow turns the solenoid on when I turn the key switch but I don't understand this technology. One of my partners mentioned PWM, Pulse Width Modulation, which may be involved but I'm not familiar with this. Can you explain to me how this system works. I have an understanding of how a solenoid works, but this configuration confounds me. Furthermore, if you can explain this to me, hopefully I can be on the way to getting my mower started.

 

[ILENGINE]

The small red wire coming off the large lug of the solenoid, that is also connected to the positive from the battery, goes to the key switch to the B+ terminal. The S terminal on the key switch supplies power back to the solenoid which could go through the safety switches, and change colors someplace, terminates as the green wire that connected to the spade terminal on the starter. With the key in the start position you should have 12v at the green wire connected to the spade terminal on the solenoid. There is no separate ground for the starter, it grounds through the engine block back to the negative ground cable on the frame to the battery.

It sounds like you are not getting power to the green wire, and could be a number of things, from corroded terminal someplace, faulty key switch, faulty safety switch, bad relay some place. You may have to get out the multimeter and start checking the start circuit wiring to find the problem.

 

[Fish]

Here is the diagram

 

[John Ambrosia]

The small red wire coming off the large lug of the solenoid, that is also connected to the positive from the battery, goes to the key switch to the B+ terminal. The S terminal on the key switch supplies power back to the solenoid which could go through the safety switches, and change colors someplace, terminates as the green wire that connected to the spade terminal on the starter. With the key in the start position you should have 12v at the green wire connected to the spade terminal on the solenoid. There is no separate ground for the starter, it grounds through the engine block back to the negative ground cable on the frame to the battery.

It sounds like you are not getting power to the green wire, and could be a number of things, from corroded terminal someplace, faulty key switch, faulty safety switch, bad relay some place. You may have to get out the multimeter and start checking the start circuit wiring to find the problem.

First of all, thank you for your amazingly quick response. Am I correct that I will need to remove the cover plate to access the key switch electronics? Once there, are the terminals you mention, B+ and S, easily recognizable? Also, I thought the green wire was a ground. I thought I followed it to the frame where it was attached to the same bolt as the battery negative/ground terminal. Am I wrong on this? Is this key switch protected by a fuse, ie. can it be something as simple as that (wishful thinking!) Lastly, I am in the market for a new multimeter, so can you recommend a brand and model to me. I don't mind spending more to get a good quality multi-use tool. Thanks again.

 

[Fish]

Fluke makes the best meters out there. Basically the solenoid is just a heavy amp switch, the keyswitch sends a signal to the solenoid to tell it to connect the starter
directly to the battery. Yes, most of the Kawasakis/Skags have a couple inline fuses, find and check them first.

 

[Rivets]

Use this procedure along with IlEngines instructions and you should be able to track down the problem. As for a multimeter, I would suggest the best one you can afford.



Electrical* problems can be very easy or very difficult, depending on four things.
1. * How well you understand basic electricity.
2. *What tools you have and know how to use.
3. *How well you follow directions.
4. *You don't overlook or assume anything and verify everything.

Remember we cannot see what you are doing. *You are our eyes, ears and fingers in solving this problem. *You must be as accurate as you can when you report back. *The two basic tools we will ask you to use are a test light and a multi-meter. *If you have an assistant when going through these tests it would be very helpful. *These steps work the best when done in order, so please don't jump around. *Now let's solve this problem.

First, check the fuse(s), check battery connections for corrosion (clean if necessary) and *voltage - above 12.5 volts should be good.*

Second, check for power from the battery to one of the large terminals on the solenoid. *One of the wires is connected directly to the battery and has power all the time so one of the large terminals should light a test light or show 12 volts on a meter at all times.*

Third, *check for power at the small terminal of the solenoid while depressing the clutch/brake pedal and holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch). If your solenoid is a four wire solenoid, check both small wire terminals as one is ground and the other is power from the ignition switch. *If your solenoid is a three wire solenoid, make sure the solenoid body is not corroded where it bolts to the chassis of the mower as this is your ground path back to the battery. *If in doubt, remove the solenoid and clean the mounting area down to bare metal. *If there is no power to the small terminal then your problem is most likely a safety switch, ignition switch or in the wiring.*

Fourth, check for power on the other large terminal of the solenoid while holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch). *If you have power what is the voltage?

Fifth, check for power at the starter while holding the key in the start position (assistant again). *If you have power what is the voltage?

Sixth, check your ground circuit back to the battery.

After you have gone through each of the above steps, let us know what happened when you did each step. *At that point we will have great info to tell you how to proceed. *Remember you are our eyes, ears, and fingers, so please be as accurate as possible.

Be as specific as possible with voltage readings as this will help diagnose your problem quicker. *If you do not know how to perform the above checks, just ask and I will try to guide you through it. *Youtube also has some videos and as you know a picture is worth a thousand words.

 

[Fish]

On the backside of most keyswitches, the terminals are usually labeled B and S, etc...

 

[John Ambrosia]

Here is the diagram

Thank you for the diagram. I am on the hunt for the problem. Hopefully, with your additional information, I will get there.

 

[John Ambrosia]

Use this procedure along with IlEngines instructions and you should be able to track down the problem. As for a multimeter, I would suggest the best one you can afford.



Electrical* problems can be very easy or very difficult, depending on four things.
1. * How well you understand basic electricity.
2. *What tools you have and know how to use.
3. *How well you follow directions.
4. *You don't overlook or assume anything and verify everything.

Remember we cannot see what you are doing. *You are our eyes, ears and fingers in solving this problem. *You must be as accurate as you can when you report back. *The two basic tools we will ask you to use are a test light and a multi-meter. *If you have an assistant when going through these tests it would be very helpful. *These steps work the best when done in order, so please don't jump around. *Now let's solve this problem.

First, check the fuse(s), check battery connections for corrosion (clean if necessary) and *voltage - above 12.5 volts should be good.*

Second, check for power from the battery to one of the large terminals on the solenoid. *One of the wires is connected directly to the battery and has power all the time so one of the large terminals should light a test light or show 12 volts on a meter at all times.*

Third, *check for power at the small terminal of the solenoid while depressing the clutch/brake pedal and holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch). If your solenoid is a four wire solenoid, check both small wire terminals as one is ground and the other is power from the ignition switch. *If your solenoid is a three wire solenoid, make sure the solenoid body is not corroded where it bolts to the chassis of the mower as this is your ground path back to the battery. *If in doubt, remove the solenoid and clean the mounting area down to bare metal. *If there is no power to the small terminal then your problem is most likely a safety switch, ignition switch or in the wiring.*

Fourth, check for power on the other large terminal of the solenoid while holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch). *If you have power what is the voltage?

Fifth, check for power at the starter while holding the key in the start position (assistant again). *If you have power what is the voltage?

Sixth, check your ground circuit back to the battery.

After you have gone through each of the above steps, let us know what happened when you did each step. *At that point we will have great info to tell you how to proceed. *Remember you are our eyes, ears, and fingers, so please be as accurate as possible.

Be as specific as possible with voltage readings as this will help diagnose your problem quicker. *If you do not know how to perform the above checks, just ask and I will try to guide you through it. *Youtube also has some videos and as you know a picture is worth a thousand words.

Thank you for all of your time and effort. The first thing I will need to do is get a digital multimeter and test light. Then I will go through your instructions step by step and report back. Thank you again- your help is much appreciated.

 

[Mad Mackie]

Most if not all newer Scag machines have a relay in the cranking circuit. This relay is usually located close to the key switch. When all the safety circuits are in the correct position for engine cranking, the electronic control module will ground the relay and when the key switch is in the start position, the relay will close and allow electrical power to go to the starter solenoid which in turn will close the high amperage switch internal to it and sends battery power to the starter motor.
On the Scag website on the left side is a link to manuals. You need the model and serial number and search thru to get the correct manual for your specific machine. Toward the end of the parts portion of these manuals is a section of electrical systems and then wiring diagrams.
Most of the cranking problems on these machines can be traced to the cranking relay or the seat switch.
Mad Mackie in CT