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Old 11-06-2007, 12:06 PM   #1
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Default Deactivating daytime running lights on 97 to 05 Park Avenues

I've never been a fan of daytime running lights that use the high beam headlights, because they are so blinding and give me headaches; after nearly getting into an accident once when the glare of an oncoming car'* DRL'* masked a stopped pickup with muddy brake lights on a shadowy road, I decided that if I ever got a car with high-beam DRL'*, I'd deactivate them posthaste.

Well, when I bought my '97 Park Avenue, guess what...high-beam DRL'* that you can't shut off unless you're in Park. Fortunately, the factory shop manual shows how the no-DRL option (RPO T62) is wired, so I was able to replicate that on my '97 PA, and posted the procedure on (replicated here).

The following procedure describes how to deactivate the DRL'* on a 1997 Buick Park Avenue by duplicating the factory RPO T62 (no DRL) wiring configuration option, and is probably applicable to most GM cars 1997-present (not just Buicks) that use high-beam DRL'* along with an automatic headlamp system. The only side effects are that the security system and perimeter lighting will no longer be able to flash the DRL'*, so only the parking lamps will come on when you activate the security system or perimeter lighting. The automatic headlamps at night and the flash-to-pass feature still work normally.

Deactivating the DRL'*. To deactivate the DRL'*, remove the driver'* side headlamp assembly; on my '97 Park Avenue, this was held in place using two thumbscrews atop the assembly, accessible from under the hood (do NOT mess with the aiming screws) and pull the assembly straight forward to pop the rear retaining pin out of its socket in the fender. After it is loose, unplug or twist and remove the turn illuminator lamp (rearmost bulb in the assembly) if necessary so you can pull the assembly out far enough to see what you're doing.

Locate the "ground" wire of the driver'* side HIGH beam headlamp (the lamp closest to the car'* centerline); on my '97 PA, this wire is black with a white stripe. You can verify that this is the wire you want by unplugging the headlamp connector and verifying that this wire is +12V when the DRL'* would be on (DAYTIME, ignition ON, headlamp switch OFF, transmission in D) and that it becomes a chassis ground when the high-beam headlamps are ON (nighttime or headlamp switch ON, with the high beams activated). Cut this wire at a spot several inches from the headlamp connector.

Carefully endcap the end of the cut wire coming from the control module (the chassis wiring harness end, NOT the headlamp assembly end), to prevent shorts. Then splice the headlamp end of the cut ground wire into the ground wire of the low-beam headlamp (solid black on my car; use a multitester to verify that it'* a ground). Solder the splice well to prevent loose connections, tape and insulate it, put everything back together, and you're done. The headlamp wiring now duplicates the factory RPO T62 wiring as described in the factory shop manual.

If you want to get fancy, you can ground the high-beam headlamp through a weatherproof 25A SPDT switch under the hood as I did - one of the plastic air box struts is a good place to put it - with one side of the switch going to the lamp control module and the other side going to a chassis ground, and the wire from the headlamp going to the center contact. This allows you to switch the car between the regular and RPO T62 configuration if desired, but don't attempt it unless you know what you're doing. Suitable weatherproof switches are available from West Marine or other boat stores.

Why this works. When operating the regular high beam headlamps (not DRL'*), the Lamp Control Module (LCM) feeds +12VDC to both headlamps separately; the passenger side headlamp grounds through a nearby chassis ground, and the left driver side headlamp grounds through the LCM itself since it has no local chassis ground. In this mode, the high beam headlamps are operating in parallel.

When the headlamps are off and the DRL'* are triggered, the LCM feeds +12VDC to the "ground" wire of the driver'* side high-beam headlamp, and the current flows in "reverse" through the driver'* side headlamp and grounds through the passenger side headlamp. In this mode, the high beam headlamps are operating in series, decreasing the current (and light output) somewhat.

On cars equipped with the RPO T62 (no DRL) option, the driver'* side headlamp is grounded to a local chassis ground instead of through the LCM, and the DRL wire from the LCM is either deleted or endcapped. The above procedure duplicates this configuration.
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