Thanks guys! I'll have to take another look at the backbox. Mine is completely missing the topper. Haven't looked to see if anything is wired internally. I'm assuming (hoping!) that's somewhere in the manual.

Did you just cut the car adapter off and crimp on an appropriate connector?

Anyone love the red vs blue? I see the original came with blue but red seems to make more sense.

Picked up the Amazon light, clipped off the car adapter, and stripped off an inch or so of wire. I looked in my backbox, I have the male adapter for the top.

I've replaced the bulb with a Comet flasher.

I don't think it matters with side I pin into a new female adapter. Just pin it in, plug it in, and confirm it's working. Do I have it right?

Picked up one of the suggested toppers from Amazon, cut off the car plug, and crimped on a pair of leads with needle nose pliers. Plugged the two leads into the socket in the backbox and fired up the pin for lamp/flasher diagnostics.

And...nothing. Doh. I don't have a crimper so it's possible that's the issue. I did check the adjustments to confirm the topper was enabled. No other flashers or GI lights are out. I'm assuming this should have fired when in flasher test. I did try reversing the pins in the connector to confirm there were no issues there.

Haven't yet measured anything from the existing connector or tried a different bulb (I replaced the stock bulb with a Comet flasher). Just making sure I didn't miss anything obvious. Will double post in Tech once I have a chance to look it over.

This may have answered it. I just tested all lamps / all flashers. It looks like you're testing the 'mars' item(?).

If so, perhaps that's my problem and it's solved after all! Will have to test it out tomorrow. Can anyone confirm that's the test?

That was it. Just testing the wrong thing. Flipped over to coil tests, navigated to Mars and BAM! Working topper.

Thanks to everyone for the assist!