Piston Slap: To Flash or Not To Flash Your CHMSL?

piston slap to flash or not to flash your chmsl

Chris writes:

I’ve noticed various new-ish cars, ranging from Kias to Lincolns, with a flash-then-steady mode on their center high-mount stop lights. Is this becoming standard? I expect it’s not federally mandated, but I can’t imagine where else it’s coming from.

More importantly, how is it being implemented? I’m thinking about grabbing one from a salvage yard in a few years.

Sajeev answers:

Yes, they’re [s]legal[/s] not illegal, but no, they ain’t factory. Mercedes tried to bring them to the US — and failed. You can buy the kit for cheap or, more shockingly, as a (high-margin?) add-on sold inside a dealership’s F&I department. I suspect you are seeing the latter in your neck of the woods, as I doubt people would install ’em otherwise.

I first saw a flashing CHMSL on a C5 Corvette at an open track event at MSR Houston. Thank goodness I was the fastest guy in the novice run, so I could pass the obnoxiousness in my trusty 1988 Cougar. That said, I installed sequential signal lights (homage to the original 1967 model) during its mild restoration in the last two years.

So who am I to judge [s]poor[/s] subjective taste?

(Sorry again for not turning my potato sideways. I’ve learned much since 2014.)

I reckon these are a box of solid state electronics, much like the sequential kits on the market today. The three wires splice into the factory harness, but I wouldn’t cannibalize one of these kits if you find one in the junkyard. The data on its safety benefits seems subjective and I doubt it’ll stop an Instagraming driver from rear-ending your ride. More to the point: no amount of flashing is more eye-catching than social media, son!

Look, I don’t necessarily practice what I preach. But if the new Mustangs and even Audi implemented sequential signal lights, perhaps I’ll successfully take the higher ground.

Off to you, Best and Brightest.

[Image: Shutterstock user Bhakpong]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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  • Ronman Ronman on Oct 24, 2016

    I noticed this yesterday on my soon-to-be father-in-law's GMC Terrain, as well as most city buses and Disney World buses...

  • 415s30 415s30 on Oct 26, 2016

    I have seen a brake light on Evos that blink three times when they hit it. I lift mostly until I need to brake, so in SF when its wet I tap my brakes to flash them to let them know. In my 240Z it's hard to see the small lights, I was thinking of putting an LED tailgate brake light strip on the back of my roll bar so it was really noticeable through the rear hatch glass. I already had someone lightly tap me and my friend's shop did a lot of work for even a small incident.

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