Federal Motor Vehicle Safety Standards (FMVSS's) give manufacturers the choice to either have the retarder activate or not activate the brake lights. It's their choice. This holds for compression brakes or exhaust brakes. Since just about all these systems are now controlled through some sort of a computer, I believe these brake lights can be set so they will or will not activate, and the setting can be changed with the right manufacturer/repair shop diagnostic computer. THERE ARE SOME NOTABLE EXCEPTIONS. When I had a 2008 Allegro Bus on a Freightliner chassis, the Jake did not activate the lights. I asked, and Tiffin reprogrammed the computer so it did, and I was happy. When I got the 2013 Bus on a Powerglide Chassis (Tiffin manufactured) the lights also did not activate. I asked Tiffin to reprogram them and after much research they found they COULD NOT. On that year Bus, there was no light that activated on the dash cluster when the compression brake came on. Without this light, when the MMDC was reprogrammed to turn the brake lights on with the compression brake on, it instead turned on the Check Engine Warning. That light could not be turned out without the maintenance computer hook up. I understand Tiffin has since put the necessary light on the dash cluster and brake light activation can again be programmed on the Powerglide chassis.
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