1974 C-100 solenoid problems

[onisius 5]

                Hi,

Have 74 C-100 with starter solenoid not clicking. If I jump 2 large terminals starter turns over strong but no

engine start. Ignition turned to first position not start position. Solenoid used to click before after a few tries now not at all. Do I have to jump solenoid + battery terminal to trigger? What position does key need to be in? When solenoid terminals jumped and engine turns with safety interlocks engaged, why won't it run? Is

there any way to jumper or bypass to to get engine to run?

                                                                                                  Thanks for any help,

                                                                                                            Onisius 

[gwest_ca-(File Mod) 10,474]

I think this diagram should match what you have.

 

Ignition switch has 4 key positions. [Off], [Run with accessories], [Run] and [start].

You should have battery voltage at the ignition coil (+) terminal with the key at [Run with accessories] and [Run] and [start]. Try them all.

 

For the starter to work the pto must be off (which closes the pto switch) and the clutch pedal down (which closes the clutch switch)

 

Also check to see if you have battery voltage at both ammeter gauge terminals. Key can be off for this test.

 

Let us know what you find.

 

Garry

[Save Old Iron 1,563]

 If I jump 2 large terminals starter turns over strong but no

engine start.

                                                                                                            Onisius 

 

 

Correct, the jumper seen in the image below will mimic a properly functioning relay. The battery voltage will be applied directly to the starter and given a good battery, battery cables and functional starter, the engine will crank as long as the blue jumper is in place.

 

 

 

There is a caution that must be used with this troubleshooting routine. This routine bypasses all PTO and Starter safety switches. DO NOT leave the PTO lever engaged as any attached implements such as a mower deck or snowthrower will "come alive" when you jumper his solenoid.

 

The engine should not be able to be started due to other safety switches in place.

 

However,

 

You should not use this troubleshooting process unless you have the PTO lever disengaged AND the spark plug wire pulled off the spark plug.

 

WE DO NOT WANT THE ENGINE TO START WHILE YOU ARE PERFORMING THIS PROCEDURE.

[Save Old Iron 1,563]

Once you confirm the battery, battery cables and starter are all functional, another jumper can be applied to the starter solenoid to bridge the battery (+) stud with the "trigger" terminal of the starter relay,

 

 

 

 

This procedure will check the electrical operation of the starter relay.

 

Same caution as above

 

There is a caution that must be used with this troubleshooting routine. This routine bypasses all PTO and Starter safety switches. DO NOT leave the PTO lever engaged as any attached implements such as a mower deck or snowthrower will "come alive" when you jumper his solenoid.

 

The engine should not be able to be started due to other safety switches in place.

 

However,

 

You should not use this troubleshooting process unless you have the PTO lever disengaged AND the spark plug wire pulled off the spark plug.

 

WE DO NOT WANT THE ENGINE TO START WHILE YOU ARE PERFORMING THIS PROCEDURE.

[Save Old Iron 1,563]

Once the starter relay is confirmed functional or replaced if defective, you can proceed on to the safety switches.

 

 

 

 

The safety switch seen in the starter circuit and the ignition circuit will most likely be more than just one switch. For example, in the starter circuit, the one safety switch shown in the diagram may actually be 2 switches wired in series. BOTH switches would have to be activated for safety function to be disengaged. In your case, both a PTO switch and and a brake pedal switch may need to function properly.

 

For power to be applied to the ignition, the seat switch (if present) and the PTO lever switch would need to be functional.

 

The number of switches (and / or relays) in the safety circuits varies with the model of the tractor in question. Some tractors may have had the safety switches removed or bypassed by previous owners. 

 

Always exercise caution when you are troubleshooting wiring involving safety switches. Review and understand the cautions I listed earlier.

[onisius 5]

SOI, 

  Thank you for your reply. In your first 2 diagrams you show the battery + cable attached to the left side of the starter solenoid and in the last one you show it attached to the right side of solenoid and starter motor to the left. Does this make a difference as to operating properly or not? I realize from my C-100 wiring diagram that a red wire has to run from the + side of the battery connection to the solenoid to the positive of ammeter and light green from negative to B on switch. My last question for now is if ammeter is bad can I jump the red and  green wires at ammeter and still run? 

                                                                                                                                  Thank you so much again,

                                                                                                                                              Onisius

[Save Old Iron 1,563]

Onisius,

 

you have a sharp eye and it is a good question.  The position of the two wires on the starter top studs does not make any difference as far as electrical performance. You may attach the wires either way to make the layout of the wires as short and convenient as possible.

[Save Old Iron 1,563]

these are the internal pieces of a starter solenoid

 

 

 

 

 

 

when you apply 12 volts to the trigger, the solenoid (on the left) forced a copper disc up against the flat bottom area of both of the top studs (on the right in the pic)

 

the copper disk acts to electrically connect the two studs together and delivery battery power to the starter.

 

when you allow the starter switch to return to the run position, the spring on the copper disk forces the copper disk away from the studs which then interrupts power to the starter.

[Save Old Iron 1,563]

My last question for now is if ammeter is bad can I jump the red and  green wires at ammeter and still run? 

                                                                                                                               

 

Yes

 

For the purpose of troubleshooting, an ammeter is nothing more than a piece of wire capable of handling a 15 to 20 amp current flow.

 

If you have ring terminals on the ammeter connections, you can fasten both the wires to the same stud on the back of the ammeter (positive or negative stud, makes no difference). Essentially you are just using one of the ammeter studs to physically fasten the two wires together,

 

 

bypassed

 

[onisius 5]

          SOI,

Thanks so very much for your prompt and as always informative response.