These folks sell just about anything LED, if there is a replacement bulb that will go in the Vipers tail light, they would have it:
www.ledtronics.com
Never had my tail light bulbs out, but maybe these??
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It is located on their:
Automotive Page
I put LED tail lights on both my trailers and they are flat out worth every penny.
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I think I paid $60 for them from Tractor Supply vs. about $7 for standard trailer tail lights. Even in the middle of the day, you can clearly see the stop and turn signals, they are that bright. Not like the incandecents which you had to be looking at VERY hard to even notice they were lit.
Next Up I'll be replacing all the running light with LED's as well. I love them.
Let us know what you find, bright tail lights will help keep people off your back bumper..