Gary,
There were a couple of excellent replies to this. Joe Curry correctly said
that a relay can't be tested with a multi-meter. But you *can* test it
with a multi-meter, a battery and a bit of wire.
First, use the resistance function on your meter to check that the
high-current circuit is open (i.e. infinite resistance). Then wire the
winding (low-current) circuit to the battery (you'll probably want to fuse
this, even though it's only temporary, if you suspect the relay may be
faulty). Re-check the high-current circuit - it should now be a closed
circuit (0, or close to 0, resistance).
While you're doing this, be *very* careful not to short-circuit anything by
letting bare wire touch things it's not supposed to touch.
Also, people have mentioned that the relay activates a high-current circuit
when there's a voltage applied to the low-currenct circuit - this is the
normal way a relay is used. But it can be used the other way, i.e. to
*de-activate* the (not necessarilly high-current) circuit when a voltage is
applied to the winding circuit. For example, if your overdrive inhibitor
switch didn't activate properly (as mine doesn't), you might connect the
winding circuit of the relay to the reverse-light circuit. Thus, when the
reverse light comes on, the high-current circuit will open (instead of the
normal configuration, where it would close) and prevent the overdrive from
being used in reverse by mistake. Most over-the-counter relays from
electrical stores do this by having three pins for the high-current
circuit. You use two of them - which two depends on the configuration you
want your relay to operate in.
Hope that helps!
Dean
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Date: Fri, 16 Feb 2001 11:12:59 -0600
From: "Gary Hutton" <hutton@evansville.net>
Subject: Re: Overdrive tranny question
Can someone explain to an electrically-challenged owner the actual
function of the horn and overdrive relays in our cars. Are they just
electrical switches instead of mechanical ones? And is there a
procedure for testing them with a multi-meter?
TIA
Gary Hutton
Newburgh, IN
76 1500
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