switch/ solenoid What's bad?

[Iplayfarmer]

Help me out here.

I just bought a Massey MF12G garden tractor, and I had to jump the starter solenoid to get it started to load it. I picked up a new solenoid on the way home, installed it, and still nothing.

Here's the deal though, the old solenoid had two big posts and one little post. The new one has two big and two little. The guy I bought them from is one of these old timers who've been around forever, knows everything and is always right, so I'm pretty sure he'd give me the right part. The only way he wouldn't have is if he didn't get a close enough look at the old one.

Would the number of little posts make that much of a difference? If not, which post do I put the switch to?

How do I check the old solenoid to see if it works? How do I check the switch? Does the switch usually ground the circuit or is the circuit already grounded?

Any help is appreciated.

 

[RonMar]

The two big posts are the high current connection between the battery and the starter motor. The two little posts are connected to the coil inside the solenoid. When current flows thru this coil, a magnetic field is generated and a piece of metal inside is drawn toward this magnetic field and forces a conductor to make contact between the two big posts. This piece of metal is spring loaded to the open position so once the current flow is removed from the little posts and the magnetic field collapses, the spring opens the connection between the big posts. There are a number of ways to operate the solenoid. The way yours operates depends upon how the tractor is wired.

You said that the original solenoid only had one small post. Was the solenoid bolted to the chassis? If so, that single small post was most likley connected to one end of the internal coil while the other end of the coil was connected to the case of the solenoid. If this is the case, turning the key to start will provide positive voltage to the single small post and the current will flow thru the coil to the chassis ground to complete the circuit and activate the solenoid.

There are two ways to determine how yours works. 1. Follow the wires from the switch and see where they lead. 2. Use a test lamp or a volt meter to determine what is on that single wire that was connected to the single small post on the original solenoid when you turn the key to start. Number 2 is usually easier Traditionally, that wire should provide +12VDC measured to ground or the negative terminal of the battery when trying to crank the engine. If yours provides +12V at that wire or will light a 12V light bulb with one end connected to the wire and the other end connected to ground, you need to connect that wire to one of the small posts on the new solenoid and make a small jumper wire to connect the other small post to chassis ground to allow current to flow thru the coil. If you don't get +12 or a light to light on that wire, let me know and I have another test to try. I am guessing it will light a light though as that is the standard configuration.

 

[Soundguy]

What Greg said about the 2 small posts going to the coil is good info, and holds true for an 'isolated' type solenoid. However.. if it is a 'bypass' style, then only 1 small wire needs to be powered,a nd the case tot he solenoid will be ground.. the other smallpost passes battery power to be hooke dup to your ignition coil ( on a gas tractor that uses a ballast resistor or other series resistance in line with the ignition in order to get hotter sparks during starting ). once you let of fthe key, the bypass terminal marked (I) ( ignition ) does nothing.

It should be easy to check both solenoids with a vom and some gator clip wires.

Soundguy

 

[Farmwithjunk]

Help me out here.

I just bought a Massey MF12G garden tractor, and I had to jump the starter solenoid to get it started to load it. I picked up a new solenoid on the way home, installed it, and still nothing.

Here's the deal though, the old solenoid had two big posts and one little post. The new one has two big and two little. The guy I bought them from is one of these old timers who've been around forever, knows everything and is always right, so I'm pretty sure he'd give me the right part. The only way he wouldn't have is if he didn't get a close enough look at the old one.

Would the number of little posts make that much of a difference? If not, which post do I put the switch to?

How do I check the old solenoid to see if it works? How do I check the switch? Does the switch usually ground the circuit or is the circuit already grounded?

Any help is appreciated.

Also, don't overlook any nuetral start switch and/or PTO switchs that may be disconnected or bad. They'll drive you bonkers.

 

[PineRidge]

Put a wire on one of the small terminals of the solenoid and ground it to the tractor chassis. Connect the other wire that was on the smaller terminal on the original solenoid to the other terminal on the new solenoid. You don't even need to hook up the other two larger wires for this test, just make sure they don't touch anything. Turn the key and if you get a click then the low voltage part of the solenoid is wired correctly and you can proceed to connecting the remaining two larger wires. Good luck!

 

[dbdartman]

Check for 12v at that small wire with the ign switch at the start position FIRST! If you don't have 12v there, start tracing back, confirm continuity through any safety switches & confirm 12v from the ign switch.

 

[Soundguy]

If it is an isolated type, thuis works fine.. If this is a bypass type.. then the wire is liable to start smoking as you are shorted to ground...

Soundguy

Put a wire on one of the small terminals of the solenoid and ground it to the tractor chassis. Connect the other wire that was on the smaller terminal on the original solenoid to the other terminal on the new solenoid. You don't even need to hook up the other two larger wires for this test, just make sure they don't touch anything. Turn the key and if you get a click then the low voltage part of the solenoid is wired correctly and you can proceed to connecting the remaining two larger wires. Good luck!

 

[Iplayfarmer]

Got it!

I ran my test light from the small wire from the switch to ground and sure enough, it lit up when I turned the key. So, then I took a small jumper wire with alligator clips that I have made up just for occasions like this and ran it from the 2nd small post to ground. I turned the key and voila!...the starter motor worked.

I'll take some time tomorrow to make and install a small jumper wire from the 2nd post to ground.

I knew I could count on you guys to come up with the right answers.

Now I just have to fix the left spindle, implement lift lever, seat, right tire, Hood Header ring,...

 

[Soundguy]

Ok.. you have the iso type. Why not just get a 2-3" piece of wire with eyelets, and attach one ont he small terminal, and the other on the mounting bolt.. Should be set then.

Soundguy

 

[PineRidge]

this is a bypass type
Soundguy

bypass type??? What is bypass type.....

Every solenoid that I have ever seen is one coil wire grounded and the other hot from the switch on start only. I would like to see a wiring diagram for the bypass type though.