The horn works fine when the car is running, but when the car is off, it works about 20% of the time. Embarrassing when I'm at a show and someone wants to hear the horn and it won't work. Is the horn relay the issue?

that's where i would start. if that doesn't solve it you'll have to bust out the volt meter and trace the power in both running and not running. what's the wiring like? original, repro, mess of splices and tape? have you ever taken the wheel off and looked at the horn switch? it could be the spot where you 'park' the steering wheel (70 was the first year for column mount locking wheel isn't it?. it could be worn or not making contact.

Wiring is original and in good shape. I've had the steering wheel off to replace the ignition switch and everything looked fine. I didn't think about the spot where the steering wheel "parks". I'll have to stop the car with wheels turned a little bit, and see if that changes things. I think it's the relay, but couldn't think of anything else. Thanks.

By the way where is the relay on a 70. I know a 69 has it out by the horn. Guy in my club says in 70 it is under the dash?

What mike said, grab your meter & get after it when it ain't working to find the part time open. As you know wires in a circuit lose continuity at the terminals/ends & I'd check all of em & seperate the pull apart connector under the steering colume & ohm it to see if the problem is under the steering wheel. I would think that the relay is still on the firewall but you'd easily spot it if it is

Had that happen about 30 years ago. It was a little corrosion on the contacts right at the horn hub on the wheel. Relay is bolted to the underside of the bottom of the dash, between park brake handle & steering column.

and i'm pretty sure 70 is the first year for a locking wheel which would put the contacts in the same spot everytime.

Will a RR horn work without a relay? I want to put one on something that just a has a 12 volt wire going to it for the beep beep sound.

If you used an add on momentary contact switch & wires of adequate gauge it'd work. The steering wheel contact, grounds the wire so there would not be a way for the steering wheel contact to open/close a hot 12V power in feed wire which the add on momentary contact switch would do. Not sure if that is what you are asking

for it to go beep beep you need to push the button twice...LOL