As many of you may recall, I replaced most all of the running, tail, and stop lights with LED assemblies I either bought or built. IMHO the lighting is great and really stands out, plus the running current for the lighting was reduced by 10 amps!!

A bit ago I posted that my cruise control had failed and I was working on a suitable electronic replacement. I had cleaned the old cruise control unit and connectors to no avail. Still didn't work, every now and then it might work but --.

What I found was that the cruise control depended on the stop lights to load the stop control line to ground when the stop switch was de-activated. The cruise control has a relay that is connected to the stop light control line and is supposed to activate when the brakes are activated. Well---by changing to LED stop lights, this line did not have a load when off and the voltage was pulled high by the rear side clearance lights, activating the cruise control relay, so the cruise control was being told not to work--GRRRRR, I completely overlooked this The reason I didn't connect these symptoms is because when I tested the cruise control after the cleaning, I did a quick run down the road and didn't turn on the lights, cruise control worked. When I tool the next trip, lights were on and the cruise didn't work. ( I always drive with the lights on, day or night!)

The old cruise control is out now and I am not putting it back but it is a lesson that was learned. With the new cruise control unit ( from a 1999 Chev 2500 truck) I will incorporate correct brake signaling and control.

If you have changed the stop lights to LED and your cruise control doesn't work, put light bulbs back in and I'll bet it works.

HTH

Thanks for that lesson.

Is it possible to build-in some form-of resistance along-with the LEDs so the system "thinks" that there are standard incandescent bulbs in-place, instead of LED's with their low power draw???

Generally, the need is to put a load in parallel - the LEDs draw very little power compared to incandescents, so the circuit has to be fooled by increasing the current draw.

The idea to change to LED beside the increased lighting effect is to reduce the power draw, and yes, you can put in a separate resister to once again allow the system to react like it has standard incandescent lamps.

Many times turn signal light do not work when changing to LEDs because the flasher unit works by a heating element that needs high current to heat thereby breaking the contact and cooling to start the cycle over again. Newer flashers are "solid state" and do not need high current to work.

On the Barth, because there are clearance lights and there is a switch to "blink" them (thank you flashing) AND they have to work with the turn signals AND the emergency flasher, the lower rear clearance lights are connected into the stop lights. Ever notice the clearance light blink 180 degrees out of sequence with the turn signals? That is why. The wiring was done this way to reduce the number of wires to and from the lights, switches, and flasher units and also used the high current draw as a function. Also incandescent bulbs do not care which side is grounded, LED lamps do. They (LEDs) will not work if voltage is reversed. IF one were to measure the voltage at the clearance lights, it would be found that the voltage may be in either polarity on either wire depending on what light function is going on. Complicated I know and I knew that some vehicles cruise control will not work if a stop light is burned out but didn't think aobut that in the Barth situation.

I did put a 1 amp resistive load on the stop light circuit and the cruise control works fine and the clearance lights (LEDs) are brighter..

Good catch! You know that you could have changed out the cruise 6 times before noting a gotcha like this!