Got my sparto today. It has two wires, red and black. I am reusing the existing harness, andI assume red/red black/black, which wires from the old harness control the brake light function? Any help might prevent me from having to find a multimeter.

 

Well your description of where these wires are is a bit cryptic, but if it's just the switch circuit for the brake light YES.
red 2 red, black 2 black

 

Well, I know that red/red/ black/black does power the brake light. I am trying to figure which wire(s) power the running light.
Not sure if I want/need full time rear light though.

 

Huh?? you need a better description of where these wires are and what the F you are trying to acomplish. Rear light for what? Running light? Brake light? if the answer is both, you will need 3 wires unless you have a module that drops the voltage for the running light.

 

I would just randomly hook them up.

 

O.K. problem solved. All hooked up.