ok i got my under tail in and started the install basicly just takin all the old stuff off the bike... i wired it real quick to see how bright the tail/brake lights are as you know theres 3 stock wires and theres 3 wire goin to my new tail lights, i hooked up the wires and it lights up but when i pull the brake they dont get brighter. i tried leaving the ground the same and swapping the other 2 and it was the same result.. lit up but not bright with the brake.. any ideas?

 

What kind of tail did you get?

 

I had a similar problem with mine and it turned out to be the spring connecting the rear brake lever to the switch had lost tension. Yours sounds more like a wiring issue though, what kind of undertail is it?

 

this one

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