i bought my bike with a aftermarket undertail on it and therefore a aftermarket brake light. when i hit the brakes it is hardley noticable. the running light is fairly bright but it just doesnt change much when i hit the brakes. HOW DO I FIX IT????

thanks guys

I don't know which brand of undertail you are using, but it sounds like they wired the running lights and the brake lights backwards. Try swapping the dimmer lights to the running lights and the brighter circuit to the brake lights.