I'm rewiring my 69 RR and wondered if I need to add the horn relay back into the wiring. I'm using a Ron Francis wiring kit and there is no mention of using a horn relay.

I'm not familiar with any of these aftermarket wiring kits, but I certainly would wire in a horn relay. Horns draw a considerable amount of current, and depending on the relatively light wiring, and relatively poor contact through the horn button and slip rings is pretty dicey

It is not current that is the issue with horns, it is polarity. The horn button connects a ground, BUT the horns are already grounded. The horn relay basically converts a negative to a positive.