BufordTJ

I've had a cruise control problem for a while now. I tried testing the usual problems after a search and all checked out. No hanging clutch pedal or brake light switch problem.
A few months ago I converted the tail lights and brake lights over to LED's, and this was the problem. Apparently the brake lights need a certain resistance in order for the CC to work. I changed the lamps back to the originals and all works fine now. But the strange thing is I have a friend with a 95 as well and he's done the same conversion with exception to still having the basket handle third brake light. I'm assuming his still has the extra resistance of the third brake light and that's why his CC still works.
I'm not sure if the roof mounted brake lights will have this problem or not, but it's worth checking.

I just thought this info could help someone else in the future.

TRM

Good to know. Had a similar issue with the instrument cluster lights. I removed the ashtray light and it apparently causes the same issue in the entire circuit. Replaced the light and all was fine again.

IXLR8

Possible, but I find that hard to believe.

If the CC uses separate switches to tell if the clutch or brake pedal have been depressed, those circuits have nothing to do with the brake light circuit and bulbs. Does that brake light switch also act as the switch for the CC?

I do know that some companies specified using plated bulb casings over the brass colored bulb casings.

mytrplseven

Per the maintenance manual: Terminal 2, plug 1 of the control unit (computer) will have ground potential from the brake light bulb filament when the brake pedal is not operated. If both brake light bulbs are simultaneously defective, the CC unit cannot function because the connection with the car ground is interrupted.

It stands to reason therefore, that when the brake pedal is depressed, this trips the computer off. I only had this reference in hand because I'm troubleshooting my cruise control.

JB 911

Travis, another user who went all led (basket handle/roof mount and tail lights) reported some other issues like the lights light up very faintly with ignition on even while not pressing the brake. Others who have half and half like your friend (and me too I did my roof mount only with leds) don't have this problem. ToreB suggested adding a resistor to the brake circuit should cure this problem. It seems like it might for yours too if you feel like tinkering with it any more. I'm on the more brake light the better team!

nine9six

Interesting thread, fellas...Subscribed

JPP

I'm experiencing the same. Switched over to all LED's and CC is no non-op. Where would you source a resistor, what kind and how do you add it in the circuit?
TIA
JP

JPP

I'm experiencing the same. Switched over to all LED's and CC is no non-op. Where would you source a resistor, what kind and how do you add it in the circuit?
TIA
JP

JPP

^^^ Oh .. and double posting when only clicking once ... can you fix that with a resistor as well? :P

2RedPorsche

600RR

The solution on my car was to add an additional (and small) LED in the rear brake light circuit after the original brake light connections. The additional resistance of the LED made the mysterious ignition-on brake light faint issue disappear. The extra LED is hidden so when it lights it doesn't display.

pp000830

.....

Jlaa

Reviving this thread - has anyone found the proper resistance to solve the "cruise control inoperative if all brake lights and CHMSL are converted to LED" problem?

Recap ... My cruise control was last used 500 miles ago in December. At that time I had Tore's LEDs in the L and R brake lights but not the CHMSL. In January, I converted the CHMSL to LED and found that I had to solder a 250 ohm resistance in parallel to the CHMSL to prevent the LED CHMSL from faintly glowing when the car's ignition was on.

This was the work - https://rennlist.com/forums/993-forum/815523-third-brake-light-led-conversion-weirdness.html

Today, March, 200 miles later, I tried using the cruise control again and find that the CC is inoperative. I suspect I am not providing enough load to the CC circuit and the CC circuit believes that all my brake bulbs are halogen and that they are all burnt out. Any ideas?

Thanks.

Jlaa

Hi folks, Okay, I confirmed that the lack of cruise control is due to the CC circuit not seeing the right resistance from the three LED-based brake lights (CHMSL + L + R). Since the resistance is not right, I suppose the CC circuit believes that there all the brake bulbs are incandescent and burnt out. Therefore, the cruise control will not operate.

I confirmed this by swapping in regular incandescent 1157 bulbs into the L + R positions and found that the cruise control works. Once I take the incandescent 1157s out and swap in the LED L + R bulbs, the cruise control no longer works.

Is the only way to fix this to inelegantly wire in a ~6 Ohm power resistor in parallel with the brake circuit? That would sure be inelegant.

nine9six

the better question is...