Help with brake light problem

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?
Suggestions?
(please respond to news group as my email is spam blocked)
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bad ground for the lower lamp assemblies

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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. ----------------- Alex __O _-\<,_ (_)/ (_)
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On Mon, 11 Aug 2003, Rogers PCS User wrote:

There is no "driving light" position. Do you mean the *parking lamp* (first click) position?

Yes. Backwards.

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 this.
DS
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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?

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The bulb is grounding through the parking light filaments in all the other bulbs that come on with the parking light switch. Check the ground for the malfunctioning bulb.
Chris
----- Original Message -----
Newsgroups: alt.trucks.chevy,alt.autos.gm,rec.autos.tech Sent: Monday, August 11, 2003 8:20 PM Subject: Re: Help with brake light problem

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