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Technical - CHMSL

Last Changed 8/3/2011

In case you didn't know CHMSL stands for Center High Mounted Stop Light, the light you have in the upper center of your vehicle that comes on only with the stop lights.

We wanted to upgrade the incandescent bulb CHMSL to LEDs.  We first check with manufacturer of the CHMSL assembly we had.  They don't believe in LED lighting.  I guess they might prefer buggy whips too.

We tried using LED bulb replacements but all the lamps we tried that fit the base that held the #922 lamps didn't work.  The replacement LED lamps have the LEDs arranged around the unit and at the most, we would have 40% of the LED facing towards the lens and therefore not providing enough light.

We also tried a couple of LED arrays.  The arrays were very bright but the red lens filtered too much of the light and gave an orange color.

The next option was to find a LED light unit that would fit where the CHMSL and had enough light to qualify as a CHMSL  We had a size problem and the new light could not be larger that the current CHMSL since the trailer end cap has a vertical crease that would mean any light larger than the recess, would have a gap on each side.

We finally found that Truck-Lite Series 21 CHMSL had the right size and was DOT qualified as a CHMSL.

CHMSL This is the CHMSL that came with the trailer.  What made the replacement so hard wasn't just the size but also, the area that the CHMSL is set into, has a vertical crease in the end cap making any light larger that the original a problem.
CHMSL What we wanted to get rid of was the #922 lamps used in the CHMSL which are hard to find and we wanted to eventually replace all incandescent lamps with LEDs.
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CHMSL We tried these LED arrays which are very bright but behind the red lens of the CHMSL, the light that cam through wasn't strong enough and looked orange.
CHMSL We found a Series 21 CHMSL from Truck-Lite was a size that would fit our needs.   We removed the current CHMSL housing. grilled holes through the existing lens and body to fish the leads to the Series 21 through.

We then screwed the Type 21 to the current body.  The Type 21 was the same height as the current body and just a touch smaller than the current lens.
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CHMSL A brighter CHMSL.
CHMSL Looks fine as it fit the spot.

And the Truck-Lite Series 21 CHMSL is made in the USA, something hard to find these days.
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