I have Crackedbacks harness in my '69 from a couple of years ago. Not sure about the taillights, but will definitely brighten your dash lights up. Would like to do my 2 other cars, but I am not into making it up from a pile of parts.
Dash lights probably due to less current draw so less voltage drop through the switch. I doubt the tail light difference would be noticable.
To really brighten the tail lights you would need to run a fused 10ga wire to the trunk. Three 30A relays. One for the tail lights and one each for left and right turn. If the brake lights are separate from the turn signals, you need one more relay. The short run from the relay to the bulb results in less voltage drop and brighter lights.
