Rick,
Unfortunately, it's hard to explain how a relay works without drawing a picture.
I'll do my best.
Basically, a relay consists of an electromagnet and three contacts (some only
have two). The three contacts are known as Common, Normally Open, and Normally
Closed. A metal switch on a spring goes between the Common and the Normally
Closed positions when the electromagnet is NOT energized (that's why it's
referred to as the "normal" position). As soon as you energize the
electromagnet, the magnetic force pulls the switch against the spring from the
Normally Closed contact to the Normally Open contact. Therefore, whatever you
have connected to the Common contact, (either power or ground) is what you see
on the Normally Closed contact when the relay is de-energized and is seen on the
Normally Open contact when the relay is energized.
For those relays that only have two contacts, they are just the Common and the
Normally Open. When the electromagnet is energized, the metal switch is pulled
against the Normally Open contact.
To test the relay, the best thing is to just put power and ground on both sides
of the electromagnet (it doesn't matter which is which). You should hear the
relay click as the switch is pulled from one contact to the other. A better
test would be to put an ohmmeter on the Common and the Normally Open contact.
When the electromagnet is energized, the resistance between these two contacts
should go from infinite to zero (or damn close).
Hope this helps. I realize that this explanation is pretty confusing, so write
me back if you need more help.
David Rupert
75701.242@compuserve.com
1967 TR4A (rigid axle)
1980 TR7 Convertible
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