Two totally different problems and solutions for the 2 problems. The horn circuit has nothing to do with the dimmer.
1. Unplug the green wire from the horn(s) and take a hot wire from the battery + to the terminal. Does the horn blow? If so you will need to go up under the dash and locate two things. The flat wiring coming down from the turn signal switch. Connect a test light to a power source and the probe to the black wire at the end of the connecter. Press the horn button. Does the light come on? If not the problem is in the horn button. If it does the problem is probably the horn relay located just above the e brake release.
2. When you pull on the turn signal lever to dim/brighten do you feel a resistance and hear a click? If not problem is in the column.
I TAKE BACK MY FIRST STATEMENT ABOUT BEING TOTALLY DIFFERENT. Is there play up and down side to side in the steering wheel?????????????? If so fixing that might fix both problems.
Agree w/464Elky....dimmer switch in column actuated by rod from signal lever sounds like not making contact. If your steering wheel (tilt?) is indeed loose, a tightening of the three bolts inside may solve your problem. Horn may also be a related issue.