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How to read the electrical diagram of a starter relay

Model: (Various brands) Various
Part: Fuse box

Video tutorial

In this drawing we see a standard 4-pin relay, marked with numbers: 30 is the power supply directly from the battery; 85 and 86 are the control coil, connected to the ignition switch; 87 is the output to the starter motor. Let's take an example in a car, which we can verify from the drawing: 85 is connected to the ignition key; 86 is connected to ground; 30 to the battery and 87 to the starter motor.

If we need to find them in an electrical diagram, the relay coil is represented by a square bracket or rectangle with 85 and 86; the contacts are 30 and 87, lines that open and close. To check its operation we can test the coil with a multimeter in Ohm mode between 85 and 86 we should read 50/120; if we want to test the contacts, without power between 30 and 87 we should have an open circuit, while powering 85/86 should close.


Posted on 1 July 2025 by ScegliAuto


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