6T5RUSH

Hopefully my experience will help solve headlight bleed over experienced by others here.

This was unknown to me for some time (the problem, that is).

After I had installed a set of relays to run my headlights direct from power rather than the factory routing up to the dash cluster, then back out to the headlights, it became known to me on a trip last year that when the low beams were on, the high beams had a very minor filament glow. Clicking on the high beams, all 4 headlights were on...bright white...as it should. Clicking back to the low beams, a faint bleed over to the high beam is seen.

My electric guru neighbor, Jim Minton, persevered by cleaning the common ground for both the low and high beams, no change. Then we pulled all 4 headlights out and cleaned all the terminals on the bulbs, disassembled the tabs in the plugs on the harness and cleaned all these metal tabs as well. Reassembled and tested again...no change...still a bleed over to the high beam bulbs when on the low beam mode.

We then double checked how the DRL's were wired in, literally disassembling and carefully reassembling the wiring in...threw power on, pulled the headlight switch out, nice bright low beams and sure enough, a little bleed over to the high beam still!!

OK, we also checked the operation of the switch at the dash, disassembling the tabs on the plug from the harness at that switch, cleaning all those tabs as well. Reassembled that, threw power on and, yup, still no change.

Now we cried "Uncle"!! Called Mark at Mad Electric, who we purchased this relay kit from and explained our issue. Mark suggested using a voltmeter to see if there is any reading on the back of the ground tab of the low beam/high beam mode of the low beam connector AND he said he had seen, not too often mind you, an instance where a run of wiring harnesses had the metal tabs crossed in the plug that goes into the back of the sealed beam headlight.

He hit the nail on the head. Apparently the driver's side low beam plug had the black wire (ground) switched in the housing with the green wire (power). We decided to swap those 2 terminals and reconnected all the headlights. Nice bright low beams with NO BLEED OVER to the high beams. Clicking the dimmer switch gives a solid bright white set of beams on all 4 lights. I'm using Sylvania Halogen bulbs.

The harness is an Electric Limited harness and is probably 10+ years old. This bleed over was never noticed prior to the installation of the relays 'cause the headlights were only getting 11.5/11.6 volts. Now that they're getting a full 14 volts, that swapped terminal allowed that faint high beam glow when in the low beam mode.

Who'd a thought that was the culprit. This sure had our tails being chased!!

So, when you really get down and dirty to trace in/isolate an electric issue, ya' sometimes have to NOT assume anything.

Onward to finishing up 4-way flashers!!



Jim
In God We Trust!

magicv8

I have seen a a few GM wiring diagrams indicating that the driver's side headlamp should be wired with that error. I have also see a few passenger side park lamp filaments switched with the brighter turn filament at the RH lamp connector.

JohnZ

Jim, that's a long-standing error on the factory wiring diagram, which Lectric Limited duplicated when they made their harnesses "exactly to the factory diagram"; I would have thought they'd have run out of the old stock by now, or reworked it.

Scott Marzahl

Glad to hear you sorted it out Jim, chasing electrons can be really frustrating at times.