I was doing some research about how a pin 30 works on a relay and basically it said that this should be wired through a fuse to the battery. I checked the voltage on the relay slot where the starter relay is supposed to go and Pin 30 has no volts, pin 86 has 12v. My question is, what should be the expected voltage on pin 30 of this slot? The truck does not start, I have not replaced the relay just yet. But it does turn on if I manually press on the relay coil.

1 Answer 1


It should have battery voltage going into the #30 pin. This is where the relay gets its power to go out through #87 to the device getting power. Before you got replacing the relay, ensure you're testing the correct pins.

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  • As drawn, that pin 30 will be permanently live ie 12V. It is not controlled via the ignition switch, but could be...
    – Solar Mike
    May 25, 2019 at 4:12
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    @SolarMike - You are right. I believe it should be permanently live. I'll adjust my answer. The purpose of the relay is to be the switching source ... why wouldn't it be live? Good catch. May 25, 2019 at 13:13
  • Pin 30 was not getting voltage when trying to crank. Ended up making my own relay where pin 30 comes from the ignition switch from yellow cable. When turning all the way to start, the yellow wire turns to 12v and starter activated as supposed to. May 25, 2019 at 22:17
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    The 30 pin is the one which provides power for what is being switched by the relay ... you DO NOT want to run it through the ignition directly, unless you want global-thermonuclear-meltdown on your hands. Really, you should have direct from the battery current going to 30, not from the ignition. May 25, 2019 at 22:37
  • Shouldn't there only be 12v on pin 30 when cranking? Other option would have been using a switch, but an ignition cylinder is like a switch. Solar Mike said 'not controlled via the ignition switch, but could be'. I assume the accurate way would have been 12v live on pin 30 and 85, but on crank would have activated ground instead on pin 86? I heard that ground is activated via PCM/ECU, but I believe it depends on the make and model. May 26, 2019 at 23:50

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