How Car Starters Work.

The figure to the left is a simple starter circuit schematic showing what the circuit looked like 70 years ago. Except for one component, it still looks pretty much the same. The main moving part was a large copper bar that was pushed down to connect two big electrical contacts. When this happened the electricity could flow to the starter motor and it would crank the engine.

The main component that has changed is the starter switch. The starter switch is now an electrical device called a starter relay or starter solenoid. It is still a switch controlling the flow of electricity from the battery to the starter, only now the switch is operated by electricity instead of by your foot.

The next image is what a starter switch circuit schematic looks like these days. It's not too tough to figure out. Most of the components are the same, starter, starter switch, battery, and of course the battery cables and ground wires.

Notice the three new parts. All three of these little switches have to be working and closed in order for the starter relay to fire and send electricity to the starter.

If any one of these switches fails open, or gets out of adjustment, or gets unplugged, the solenoid won't even click.

If the solenoid clicks, the three switches above are all ok.


Before you start blindly buying new parts, take a real good look at the wires that connect the battery and the starter.

The prime candidate is where the positive post of the battery is connected to the large wire that supplies electricity to all the electrical devices on your car. Because of acid vapor venting from the battery this spot is particularly vulnerable to corrosion. It is often hidden away where the post touches the clamp, and can't be detected except by visual inspection or detection of the heat generated when current is flowing.


This is a simple schematic drawing of a very simple starter circuit. In the early days of electric starters, this is pretty much what they looked like. The starter switch was a big copper bar that you pushed with your foot so that it shorted out the main contacts allowing electricity to get from the battery to the starter motor. You had to overcome the resistance of a big spring to make it work...

 

Before you start blindly buying new parts, take a real good look at the wires that connect the battery and the starter.

The most common cause of a no-crank condition for any car is poor connections at the battery.

The prime candidate is where the positive post of the battery is connected to the large wire that supplies electricity to all the electrical devices on your car. Because of acid vapor venting from the battery this spot is particularly vulnerable to corrosion. It is often hidden away where the post touches the clamp, and can't be detected except by visual inspection and detection of the heat generated when current is flowing.

This is what a starter switch circuit schematic looks like these days. It's not too tough to figure out. If your car has an automatic transmission, you'll have a neutral safety switch. If your car has a manual transmission, you'll have a clutch safety switch.

All three of these little switches have to be working and closed in order for the starter relay to energize and send electricity to the starter.

If any one of these switches fails open, or gets out of adjustment, or gets unplugged, the solenoid won't even click. This is an important symptom.

If the solenoid clicks, the three switches above are all ok.


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