1990 heritage softail ignition switch diagram
 

I put a new ignition switch on the bike and hook the wires back up and now the brake light is not coming on. Not sure which wire controls that.

The ignition switch divides power into three circuits (there are three circuit breakers under the dash panel. they are ignition, lights and accessories. The brake light is powered by the accessory circuit.

The brake light works only when key is turned to accessory and then I turn it to lights/on its light up red and stays solid but when pressing break it doesn't go off and on just a constant red light

Try this site using your VIN
https://serviceinfo.harley-davidson....cle/lookupForm

https://cimg8.ibsrv.net/gimg/www.hdf...ba95066c79.png
Brake light gets power from the ACC circuit breaker thru an Orange wire

When you are checking your brake light are you checking with both the foot lever and the hand lever??