carpe dm

I would like to wire my lights so that the low beams stay on when I select the "high" beams. This gives significantly better light when highs are needed. I wonder if any of you have done this or whether there are problems of current draw or heat which would prevent this modification. Any ideas and/or directions would be appreciated. Thanks :confused:

ShanMan14

Good question, I wonder why it's not that way to begin with? Heat, voltage draw???

99HT

First I do not think it is legal, but it will also put more drain on the alternator.

The BCM controls the lights. You would need new software for it or you will have to modify the hardware to achieve your goals.

There is a possibility that you could use diodes to force both light relays on, but the BCM has the ability to sense if outputs are on. The software may not like any mod you might do.

LoneStarFRC

On your stock setup both sets come on when you pull back on the lever (as in "flash to pass"). I haven't studied the schematic or anything, but it would probably take a hardware modification of some sort.

Zpilot

There is a cheap mod for doing this on F-bodies (did it on my '98 Z28). You just connect two wires in the dash with one of those plastic clip splicing thingies. I can't make sense of the wiring diagrams to figure out which two might work on the C5. I bought a module from some vendor to do it on my Tahoe.

Eric94

I know that you can buy a relay for chevy trucks that does this job. I'm sure someone could figure out how to do that with the C5

99HT

Chevy trucks and F bodies do not have a BCM controlling things. You will have to modify the BCM. It may be possible to short or use diodes to force both relays on, but again, the BCM may not like it. If anyone wants to be the guinea pig, we can work it out.

Black Rain

There is a cheap and easy harness setup that allows you to keep both the high and low beam lights turned on© I bought a couple of them from one of the Forum vendors early on© They are manufactured by Competition Limited and sold under a variety of names ¥ CarShow, etc©¤ HCV ¥Carl¤ runs them on his car© A better setup, but more work and money is the E-Code T84 Headlight setup, but this is more work©

As far as the load requirements, etc© I am running this exact same setup on my 2001 Jeep Grand Cherokee Limited with Piaa Superwhite Bulbs© The real improvement comes from doing a direct wire setup with this harness pulling the power directly from the source© The additional 3 volts provides a LOT more light©

Let me know if you can't find the harness from the vendors© I have one still left new in the packaging© Paid approximately $55 + shipping each© :chevy

carpe dm

Thank you all for your comments and ideas. I am going to track this down, but the BCM connection sounds like a potential problem. If I can get it done, I will post details. Thanks again.

carpe dm

Black Rain: Thanks for your info and offer. I am going to check into it and may get back to you.

Zpilot

Just curious. What does the BCM do if it senses the low beams on when the high beams are on? What is the worst that can happen? Again, just curious.

99HT

Without seeing a BCM schematic or knowing exactly what the BCM software does, I cannot answer your accurately. I am looking at a BCM PCB and at the service manual right now to guess at an answer. The BCM knows when any relay it controls is on, because it commanded it on in response to the driver throwing a switch. It also has many inputs that monitor relay outputs to confirm switching.

Very few things in a C5 are controlled directly by the driver. Almost every button and switch go directly to the BCM or to one off the many distributed microprocessors around the C5. Every relay driver circuit on the BCM has short circuit detection to sense a relay coil or wiring short and a sense circuit to tell if the relay is switched to ground. Most of the relays the BCM controls have +12 volts constantly on the positive coil terminal.

If you change the wiring in a C5, the BCM may or may not be able to sense it. It depends if the function you are modifying has a readback sense input fed back to the BCM. It also depends if the BCM has the software to utilize this input. You can just modify the wiring and see if the BCM reports an error message. You can also go through the service manual schematics and verify if the specific circuit you want to modify has the readback circuit.

The BCM relay drivers havehand now

,

can only indirectly tell if

99HT

OK..I am a an idiot. Being lazy, I made some assumptions about the C5 headlights without digging into the service manual. All my comments about the BCM were wrong in relation to the headlights. The BCM has nothing to do with controlling the headlights. I even ripped out my BCM and turned on the lights to confirm this. After finally digging into the service manual I now have the real answer. Sometimes you have to check the facts before typing on the keyboard.

The C5 headlight system is very similar to many GM vehicles. The turn signal/headlight stalk controls the lights directly. The BCM only is involved with sensing if the headlight doors are open and closed. One thing that I find disturbing is that no relay is between the headlight control stalk switch and the headlights. The relay is on the input side of the stalk. All headlamp current flows through the stalk switch. I would be careful forcing hi and low beams on at the same time. The stalk switch may fail prematurely.

Black Rain

That's the beauty of the Comp Ltd© / Car Show Harness setup in that it has a set of relays and inline fusible links as part of the assembly© I know that HCV is running 100 W / 130 W Headlamps in his C5 with this same harness© I ran this setup in my 2000 Coupe with no problems© The T84 Euro Headlamp assembly, with relays and 10ga stranded wire is a lot more work, but seems to be the best setup© If your not up to spending several hours doing the changeout, the hi~lo harness is a much easier solution to getting better lighting© I know when I was running my Piaa's and Low Beams before the installation, when I went to high beam I actually had less light than when I was running lows and the Piaa's© Good luck :cheers:

Zpilot

Anyone know of a vendor or is this being chalked up to "no longer manufactured?"

LT1GMC

Since the headlite stalk is the main switch, how about making its outputs(the hi and low beam wires to the headlites) the drivers to new relays that have a direct connection to Battery, which would also allow you to wire from the hi beam relay to turn on the low beam relay, no diodes needed, and no extra draw on the stalk switch.!!

Come to think of it, maybe that would cure the problem my new Z06 has, headlites slightly dimming when anything else happens on the car, like the turn signal on, or the ac cycling.


[Modified by LT1GMC, 6:32 AM 8/26/2001]

carpe dm

Great discussion! LT1GMC, you have a good point about the relays. Black Rain, you still have that hi-lo harness?