Tiger cub intermittently won’t start

[Billybobscalps]

I have an older Scag tiger cub. The model number is STC48A–20CV. For the past six months or so, the mower has an intermittent starting problem. I replaced the battery in the spring. After sitting for several days, when turning the key on sometimes nothing happens at all - no click or anything. For a while, it seemed if I pulled the PTO switch on and then off, after one or a few times the mower would crank. Lately that hasn’t seemed to work. I do get a strong click from the PTO when I turn the PTO switch on and off with the key in the on position(mower not running) so I believe the PTO switch is working fine. I have cleaned and tested the four other safety switches for continuity and they all have continuity. When the key finally makes the engine crank over, the starter cranks strong and the mower fires right up. Twice in the last 20 hours, the engine has just quit while cutting. It cranked right back up both times. Typically once the mower has started the first time, it can be turned off and back on and starts normally.
Today, after trying to start the mower many times, I decided to jumper the solenoid terminals with the switch in the on position. When I laid a screwdriver across the posts, I could hear the starter spinning up, but the bendix did not engage the flywheel. After a couple more tries simply turning key switch, the motor finally fired right up and ran great.
I am a little technically challenged, but I would love some ideas on what may be going on.

Thank you very much for the help.

 

[bertsmobile1]

I will forgive you for this because when you looked in the back of your parts book that you got with the mower or downloaded because you lost it Scag do not bother to show the switch positions
If they did you would have seen that in your switch there are 3 individual sets of connectors
1 turns the PTO on & off
1 completes the cranking circuit
1 activates the engine cut out
So just because 1 pair are working, does not mean that all 3 sets are working

The connector works flat to flat on the pins
So in the off position 1 pair should have continuity and the other 2 should not
This one pair is the cranking circuit which should be the light blue to red
If you jump those positions the engine should crank when you turn the key to start ( providing the rest of the system is in the right positions )
IF not then the module is bad $$$$$
But before opening your wallet, pull the module plug saturate it with whatever you have WD 40 - Brake Cleaner - contact cleaner then connect & disconnect it several times as the plug is prone to corrosion.

 

[Billybobscalps]

I will forgive you for this because when you looked in the back of your parts book that you got with the mower or downloaded because you lost it Scag do not bother to show the switch positions
If they did you would have seen that in your switch there are 3 individual sets of connectors
1 turns the PTO on & off
1 completes the cranking circuit
1 activates the engine cut out
So just because 1 pair are working, does not mean that all 3 sets are working

The connector works flat to flat on the pins
So in the off position 1 pair should have continuity and the other 2 should not
This one pair is the cranking circuit which should be the light blue to red
If you jump those positions the engine should crank when you turn the key to start ( providing the rest of the system is in the right positions )
IF not then the module is bad $$$$$
But before opening your wallet, pull the module plug saturate it with whatever you have WD 40 - Brake Cleaner - contact cleaner then connect & disconnect it several times as the plug is prone to corrosion.

Thank you for this info. I am a bit out of my league on electronics but I will check this out and maybe post back with a picture as well. I appreciate you taking the time to answer!

 

[Billybobscalps]

I am trying to open this plug to clean it up. The whole mower is grimy and dirty. The part that comes out of the module is brittle and breaking up when it try to pull it apart. I need to get a picture of the ignition switch. I cleaned it. It has a single yellow wire and five other wires under the main plug on the switch.

 

[bertsmobile1]

I can almost guarantee you have now found the problem
The wires & terminals inside that plug will be corroded and possabilly some broken at the end of the crimp .
Just finished replacing the loom on a Z Master that I have been patching up & bypassing for several years
So problems now as you will need a new plug, terminals & a crimper
When I do them I place a couple of pieces of heat shrink over the wire & terminal crimp to strengthen the end & prevent the wire breaking at the crimp ( boy are they hard to find )
ZTR's in particular have problems with their wiring because there is no hood to keep the wires out of the sun & free from moisture & debris .
If you are lucky then Star will ship in with the part numbers for the two plug ends, otherwise go to your favourite car parts place and get a plug kit with the same number ( or more ) of wires
When you have finished, slather both sides of both plugs with lanolin grease
And belts & braces approach is to slide some rubber tubing over the whole shooting match to protect the plug from sunlight , heat , dirt & water ( old inner tube works well ).
I have a lot of old motorcycles with skinny tyres ( 1.75 to 2.75 X 19 ) so have plenty of dead inner tubes , mountain bike inner tubes also work well just make sure they are tight on the top & open at the bottom so they will drain .