Does anyone know how to fix a horn on a 90 accord LX?

 

It depends on the problem, so you have to troubleshoot first.

What other problems are you having with your car right now? Did this problem occur right after any work done on the car?

The easiest thing to check is the fuse for the horn. The cover for the fuse box has labels. If the fuse is good, then try switching the horn relay with an identical working relay nearby.

 

Ok, this has been a problem since I got the car. Is this found under the hood, or dash?

 

The problem may be:

• under-hood Fuse No. 25 (20A);
• wiring;
• horn switch;
• poor contacts or connections at the horn slip ring (located inside the steering wheel).

Your 1990 Accord doesn't have or use a horn relay.