I've rewired my brake lights to eliminate the incandescent bulb and use strictly the LED's. So far, so good. They work fine, and give precedence to turn signals when the brakes and signals are active, and flash normally...most of the time.

There are a couple of problems:

1.)When the brakes are pressed, the signals hyper flash.

2.)When I signal with the cruise control set, the cruise cancels.

3.)Under heavy acceleration with the signals active the engine loses power at the same intermittent rate as the signal flash.

I used a trailer wiring converter box to do the bulk of the work, but since the (factory) brake lights are not solid-state, I had to run power from the battery, through an inline fuse, to the brake pedal position sensor (which I unhooked and wired to my liking), and to the converter box. I have completely bypassed the factory brake light system. The car shouldn't know when the brake lights are lit unless it reads the negative, in which case I suppose I can just run a separate ground system.

Would the BCM be monitoring the state of the brake lights (via the negative from the light housing) and affecting the VDC thereby canceling the Cruise and cutting the throttle?

Any ideas? This is killing me.

Me -> <- My car

 

I guess you didn’t want to carry it over to the thread I linked

As for the hyper flash - it was very difficult for me to cut voltage to the OEM bulb (turn signal) - we wired various resistors and it gave intermittent fits... my solution as ghetto as it seems was to wrap bulb in foil. This way the BCM has no idea the blinker isn’t working and you cant see the illumination at all.

BTW, you can splice into the rear defroster or Bose sub (if equipped) for continuous power - instead of running all the way from battery.

 

I ran the power from the battery because I'd have to go from the brake pedal to the trunk anyhow, so it wasn't much more work to run the wire a little bit farther. They hyper flash is ONLY when the brakes are applied...weird...and it's a little late to put bulbs in the factory spot. I snipped the connector off and put the resistor in there to regulate the flash. I don't understand how the flash rate could change when the brakes are applied, because the resistance doesn't change!

 

yeah, the hyper flash while braking is a bit odd... the BSM does do funny things. Since you took a different approach, I'm not sure what will work - but I had to wire in a relay between the brake signal and the module because there was intermittent voltage that made one side stay bright for a few seconds after brake was released... but I'm not exactly sure something like that would cause your issue – I’m sure you’ve already used relays where needed?

 

No relays were used. I was able to avoid them by using the trailer converter module. A bit ghetto, but it was far easier...at the time. I'm sure there was a far better way to do this, but I wanted to do as much of it myself as possible, and w/o having to spend $150 for parts/shipping. I have a few tricks up my sleeve yet, but I'm still so confused/ignorant as to why ANY of this would interfere with the CC and ECU. I suppose I'll figure it out in time and with a little tinkering. If you have any sort of epiphany or stumble across any related info, let me know.

Also, do you know what the BCM monitors as far as knowing when the brakes are pressed? I think the position sensor on the pedal (higher of the two) is normally closed, and since I have it unhooked, it is open now, possibly causing the BCM to crap its pants and act stupid. Does this sound probable, or just crazy?

 

I definitely think having the BCM not recognize the brake function is causing your problems. However, I don’t know why it would cut power to throttle... your CC issue could be caused by this though... it might be more work than necessary to chase down all the gremlins - but I guess you're this far in and seem determined, I hope it works out

 

I'm having a hard time visualizing how you did this with the resistor, but one possibility is that when you are doing brake and signaling, it is basically bypassing the resistor. The brake light path through the LED's would be the low resistance path and therefore not use your resistor at all (if resistor is wired in parallel like most hyperflash-fixing load resistors). As for the cruise control cancelling, it makes perfect sense to me. When you hit the brakes when on cruise control, cruise always turns off. You wired the turn signals directly into the brakes, so when you turn, the BCM senses the brake lights are on, therefore it thinks the brakes are applied. I hope you don't start running into VDC or ABS issues when you have your turn signal on. Keep us posted. Sounds like you need to start diode isolating the brake and turn wires.

 

Ah, and now we reach the outer limits of my electrical knowledge. I have one last idea, let me know if this is stupid. I utilized the factory ground/negative within the brake light housing. Is it possible that this runs back through the BCM instead of to the battery? This would allow the BCM to continue to monitor the status of the brake lights, causing the problems with the cruise...in my mind.

Also, if I were to wire the resistor in-line instead of in parallel, would that (possibly) fix the hyperflash situation?

 

I was not able to get resistors to work in any fashion - different sizes, different configurations, always caused fits.... but then again, my situation was different were I was using resistors.

 

I think I'll give it a try tonight...fingers crossed. I am also going to use a different ground to see if i can solve the CC problem. the resistors are working fine for the turn signals alone, so it is a possibility that the brakes are just bypassing the resistors. ill try to solve this by rewiring the resistors and/or adding a traditional light in the trunk, in-line on the brake wires to mandate resistance there. I'll conduct my experiments one at a time (scientifically) so I can isolate the problem and share mt findings with everyone!

 

I look fwd to your results!

BTW, do you plan to paint the OEM signal portion of the lens? I imagine thats your intention...

 

yeah, keep us posted! i did the same, but did it differently. i ended up with a little box with four wires. ground, turn signal in, brake signal in, and one out for the lights. it works great.
im alil confused how your setup works, probably has something to do with how the trailer wiring converter thing works. what wires does it have on it?

 

The brake switch serves two purposes - one contact goes to the lights, the other contact goes to the ECU. You NEED the signal going to the ECU otherwise you'll have CC issues.

It definately sounds like you are having backfeeding issues (obviously). It may help to draw out exactly how you wired everything up.

 

There are two brake switches. One, I assume, is for the ABS, the other to the ECU and lights. I need to know which wire goes to the ECU and which is for the lights. I don't have access to my tools or garage till around 10pm tonight, and I have no idea where my voltmeter went, so this stuff will likely have to be put on hold till tomorrow.

 

any updates?