how relay works ? Options

[jimkelly]

and can some describe how a relay works?

is it that HIGH AMPERAGE thru 85 and 86 operate a switch, and when switched send LOW AMPERAGE thru 30 and 87? what is 87A's purpose?

[jimkelly]

freakin ingenious.

since our cars are run from a 12v battery, how does current know to be high or low, simply by the diameter of the wire it passes thru, or the draw of the item being run?

I assume running a circuit with a relay is cheaper than running a circuit thru a switch that can handle more current because of the cost of a better switch and the cost of running more heavy wire throughout the car?

I think I am beigining to understand the purpose of a relay, visually.

thanks guys (IMG:style_emoticons/default/idea.gif)

i think image is correct?

[pcar916]

...
i think image is correct?

30 is always a permanent ground. You can check it with an ohmmeter to a chassis ground point.

[Dave_Darling]

30 is always a permanent ground.

No, 30 should be the "hot" line! The relay will connect 30 to either 87a (when there is no voltage difference between 85 and 86) or to 87 (when there is a voltage difference between 85 and 86). Most of the relays have either constant power or switched power connected to 30. I can't think of one that has ground connected there.

--DD