Ohm-meters are of little use in diagnosis when looking for bad connections.
By their very nature they are variable in resistance, and the amount of
current you pass through them can itself cause the resistance to vary. The
only sure way is to take voltage measurements both off and on load. Off
load with the ignition on you should see 12v one side of the switch. If you
operate the brake pedal and you *still* only have 12v one side of the
switch, the switch is bad. If you have 12v both sides of the switch then
the wiring back towards the lights is bad. If you now don't have 12v
*either* side of the switch then there is a bad connection back towards the
ignition switch. You may have more than one problem of course, and
generally you can only diagnose them one at a time, the next problem not
revealing itself until the previous one has been fixed.
PaulH.
----- Original Message -----
From: "Roger Wilt" <rdwilt@pol.net>
To: <mgs@autox.team.net>
Sent: Sunday, August 08, 2004 9:19 PM
Subject: TD brake light..more info
> My confusion is that when the brake is depressed, the Ohm reading between
> the 2 contact points of the brake switch, drops to 0 - Signifying it is
> working correctly.??? The volt meter however shows + voltage in the hot
> wire contact (other tester tip is grounded to the frame) before the brake
is
> depressed, but drops to 0 after the brakes are depressed. HUH???
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