Cannot get my horn to work on my "68 GMC

[gipper]

I have a nearly restored 1968 GMC Stepside. It had an aftermarket steering wheel in it which the horn was never installed. I found an original steering wheel and installed along with a new turn signal switch. I know that the switch is installed correctly. I cannot get the horn to work. If I put a jumper from the battery to the horn, it works. I have a brand new horn relay and the red wire at the horn relay has power. The black horn wire under the hood is not connected to anything, the green wire is plugged into the horn and the red wire runs to the positive post of the battery. I tried grounding the black wire under the hood and that did nothing. I need help!

[Longhorn 70]

can you run a jumper from 12 volts to the coil of the horn relay? You can tell which is the coil by using a DMM in the ohms scale on the low range. Touch the ohm meter lead to the case of the horn relay and the other lead to each tab on the horn relay. The one that registers is the coil. Make sure the relay is grounded and touch 12 volts to that same coil lead. You should hear the relay click. if not, you have found the problem.

If it does click, when it is clicked, touch the ohm meter leads to the other 2 terminals. It should read close to 0 ohms. If not, there you go again.

Good luck