Solenoids 101

First up some basic Solenoids 101 education to help you understand how simple a Solenoid really is and not be frightened by all the wires you see attached to it. A solenoid is really just a big Relay that can handle the high amps required to turn over the starter motor when you turn the Ignition Key to Starter. Or to describe it another way, it is a little electric switch that is used to switch on a bigger electric switch.

The solenoid is normally found mounted to the transfer housing, just above the starter motor.

The job of the solenoid is to provide a connection between the high amperage cable from the battery to the starter motor when you turn the key to 'Start'. The starter motor is just a high torque electric motor that works in short bursts of energy when required, but draws a lot of power from the battery when it does so it needs big fat wires.

The solenoid requires only three wires to make it work, the first is the big fat high amperage cable coming from the + side of the Battery and it goes to one of the terminal bolts on the Solenoid. A slightly smaller big fat cable goes from the other bolt on the Solenoid to the terminal on the Starter Motor. The third wire should be White with a Red trace and it connects to the small spade/tab terminal located between the two posts, and is provide positive power via the ignition key.

The rest of the wires you see attached to the solenoid are just attached to terminals to that connect them to the power cable from the Battery to supply power for other functions on the Moke and have nothing to do with the function of the Solenoid.

When you turn the ignition key(the small switch/low amps), an electronic circuit is created via the small White/Red wire which in turns causes a lump of metal inside the solenoid to shut across the other end of the two terminal posts(the Big switch/high amps) and thus power from the battery gets to the starter motor.

Moke Solenoid Push Button Type

Problem Solving the Solenoid.

There are really only a few things that can go wrong.

  1. The low amp circuit is broken and not switching the high amp switch.
  2. The high amp switch is no longer making a clean contact with each of the terminal posts
  3. The high amp switch has welded itself to the two terminal posts.

The high amp switch has welded itself to the two terminal posts.

Taking the easiest to identify first, Number #3, this will be evident by the starter motor still engaging of spinning over when the key is no longer in the 'start' position. For the first few times a belt with a solid object on the solenoid can dislodge it, but over time it may happen more frequently.

The low amp circuit is broken and not switching the high amp switch.

When the ignition key is turned to the Start position the power to the solenoid should cause a reasonably  loud dull thud that can be heard or felt in the Solenoid. If you turn the key and you don't hear or feel the thud in the solenoid then you need to do a simple test to determine if the problem is inside the Solenoid or with the ignition key wiring.

The White/Red wire is simply a positive feed from the battery cable terminal that has gone to the ignition switch via a big fat brown wire and that comes back to the solenoid when the key goes to start.You can remove the ignition switch from the circuit by using a small piece of wire or even a screw driver or anything metal to make contact from the terminal pst with the battery cable on it to the small spade/tab terminal where the White/Red wire normally goes. This will provide a positive feed straight into the solenoid and you should hear or feel the dull thud as the lump of metal in the solenoid moves into place and the starter motor should engage.

If you do not hear or feel the dull thud then the solenoid is faulty.

If the solenoid does engage then there maybe a problem with the wire and/or contacts between the solenoid and the ignition switch and back to t he battery cable cause the ignition key not to engage the solenoid.

The high amp switch is no longer making a clean contact with each of the terminal posts.

If you are getting the dull thud of the solenoid activating but no power getting through to the starter motor then you either have a problem with the high amp contacts inside the solenoid or there is a problem in the starter motor preventing it from turning over.
To eliminate the terminals inside the solenoid as the cause of the problem you can use a thick screwdriver or thick piece of metal to short between the two terminal posts, and thus bypass the contacts inside the solenoid. Because we are playing with the high amperage circuit you need to use a thick metal object and expect a lot of spark and 'arc wleding' to occur when you make contact. And it does leave a scar on your screwdriver.
If shorting the two terminals fires up the starter motor then the problem is inside your solenoid, if it doesn't then you need to look at your starter motor.

Types of Solenoids

There are three styles of solenoid found on the Mokes normally, two are factory fitted and the third is a generic looking after market replacement.

The most common on the Moke is the square block with cylinder while my preferred one is a barrel or cylinder with a push button on the end that allows you to bypass the ignition key and engage the solenoid with your head under the bonnet.