2000 GMC Savanah 3500
With headlight switch in OFF position the brake lights work normally.
With headlight switch in either ON or driving light position: brake
lights on left and right stay on unless brake is pressed, then they go
off (backwards yes?) but the top center brake light continues to work
normally - off until brakes are pressed then on.
Dealer says it is probably the brake switch or a relay. However they say
it may take quite a while to diagnose and they have to charge for the
time. Can I troubleshoot this myself?
(please respond to news group as my email is spam blocked)
That's my guess too. I would go to the light fictures and find where they
ground to the vehicle. I would then pull the connection and clean the
connection and re-asseble.
There is no "driving light" position. Do you mean the *parking lamp*
(first click) position?
The Center High Mount Brake Light is on a separate switch contact.
There is no relay in the brake lamp circuit.
Well, they do have to charge for diagnostic time, but the brake lamp
circuit is *very* simple, so I can't really see it taking a lot of time.
Are you handy with a voltmeter, continuity tester and/or test light?
Most likely cause here is a faulty brake lamp switch. Second most likely
is a wiring problem. Faulty grounds can cause crossed-up functioning like
The bad ground therory is good but since the bulbs act normally until you
apply power to the park lamp wire I say the ground is good
Does the truck have a pig tail for a trailer if so check there first
also have you had any bulbs replaced recently?
The bulb is grounding through the parking light filaments in all the other
that come on with the parking light switch.
Check the ground for the malfunctioning bulb.
----- Original Message -----
Sent: Monday, August 11, 2003 8:20 PM
Subject: Re: Help with brake light problem
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