The starter solenoid is essential in having a car turn on and function properly. It is a glorified relay that handles a lot of amps. A lot of people working on their own cars have trouble figuring out what wires go where on a starter solenoid and we’re here to help clarify things.
Though there may be different models of starter solenoids they carry various similarities which we will cover in more detail below.
In general, there will be three connection points on a starter solenoid with one going to the positive hot battery terminal, one going to the starter, and one going to the signal wire/ ignition switch.
For another perhaps easier mental picture of the starter solenoid wiring, we’ve attached the starter solenoid wiring diagram below. (1)
What Wires Go to a Starter with Solenoid Attached (3 Terminals Explained)
A starter with the solenoid attached will have the solenoid directly mounted above the starter as shown below. This is a common type.
Usually, on common starter solenoids that have the solenoid attached to the starter you can see 2 large connection points, one will be allocated for the positive battery cable or terminal also known as a battery starter.
The next common connection point you’re going to see is reserved for the starter. This wire will help the starter fire.
What Wires Go to a Starter with Solenoid Separate (Divorced Solenoid)
Very similar to our other solenoid this is a divorced solenoid that is not connected to the starter. It basically has the same exact idea and solenoid wiring except the battery inputs are on the sides. It is extremely simplistic in its design.
Basically, it created a magnetic field to get the plungers to make a connection between the larger posts that causes the starter to spin over. (2)
Finally, the last common point and smallest is reserved for the signal wire.
Differences in Different Solenoid Models and Wiring
The biggest differences we have illustrated above are those between the models where the solenoid is mounted on the starter and the divorced starter solenoid where it is outside. Though this is a stark difference usually the wiring is still the same and offers no real change aside from what side you need to attach each wire.
Because each car manufacturer may use different suppliers there are many different looks for starter solenoids. Some are round, some can be rectangular in shape and the inner workings like the coils can be different. Overall however they will use the same wiring as we discussed above regardless of their visual appearance.
3 Post Starter Solenoid vs 4 Post Solenoid
With the 4 posts, the ground is the frame of the solenoid. With a four-post solenoid, the frame is not actually the ground, so when you connect it the fourth post needs to go to the ground. The reason the old ones used the frame as the ground was because of a lack of switches, with never equipment and the number of switches it’s common to see the fourth post for grounding.
There will sometimes be a space for a grounding wire to be added but usually, the ground will go right through the frame and you will not have a separate entry point for that, most people choose to leave this port bare though we do recommend you ground because of some of the new solenoids having a lot of switches that require this ground.
Does the Wiring Matter?
The one terminal that doesn’t matter is the positive terminal, as long as it’s connected to one of the terminals it should work properly.
Starter solenoid wiring in general requires 3 types of wire, the positive-going to the hot battery terminal, the wire going to the starter, and then finally the wire going to the ignition switch. In some cases, you may also need a ground wire as well if it is a 4-post-started solenoid.
Starter solenoids are simple devices that use an electromagnetic current to fire and can easily be replaced. We hope our guide helped you whether you are replacing your starter solenoid or just testing.
Take a look at some of our related articles below.
(1) mental picture – https://www.psychologytoday.com/us/blog/the-integrationist/201306/7-tips-creating-positive-mental-imagery
(2) magnetic field – https://www.britannica.com/science/magnetic-field
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