https://www.st-owners.com/forums/threads/st1300-audiovox-ccs-100-troubleshooting.119551/

Brake Wire Connection:
The purple wire from the cruise control servo must be connected to the
positive side of your brake switch. Normally the rear brake switch has
the easiest access. Connect the purple cruise control wire to the side
of the brake switch that usually has 0 Volts DC but +12 Volts DC when
you step on the brakes. You can also connect the purple cruise control
wire to your taillight brake wire but you'll also need a SPDT relay in
the circuit. If you have LED taillights or have even added accessory LED
brake lights you need to use a relay. The purple cruise control wire
can't sense ground through an LED.

There are some links there to workarounds :o)

On 5/6/2020 3:33 PM, OlRivrRat wrote:
>               Dennis & Dug or WeEMHTA
>
>       Very interesting ~ So is there a way to add a resistance that will make the CC happy but will not degrade the
>
> LED Output ~
>
>
>
> On 6 May , 2020, at 3:44 PM, Dug Smith wrote:
>
>> Because the cruise control uses the brake light to trigger disengaging, it checks the brake light circuit is working before it'll engage, too :o(
>>
>> toodle pip,
>> --
>>        Dug Smith         | Terry Pratchett: It's almost
>> (mailto:dug@dugbert.com) |  impossible to ride a rock and roll
>> (http://www.dugbert.com) |  motorbike and stay on for three verses.
>>
>> On 5/6/2020 1:51 PM, OlRivrRat wrote:
>>>                  To the Vanagon Electrics Wizards
>>>          I would not have been surprised to discover that My CC Would Not DisEngage
>>> with Brake Apply after LED install but what I am encountering is that the CC Will Not
>>> Engage now that I have LED Brake Lights > I'm Puzzled ~
>>> Again  >>  AudioVox CCS-100 + Speedo Mounted VSS + Dakota Digi SGI5 ~
>>>                                                          ORR ~ DeanB
>