Quiet horn has me thinking electrical problem?

So I bought a couple of used horns to replace my quiet Alto one and the driver's side which to be totally appeared dead. The new used horn, when hooked up to a battery, is loud and appears to be functioning. Unfortunately, when I set up in place of the old one, its quiet also. Is there something in my electrical system that is dampening the flow of electricity? I've cleaned all of the terminals in the fuse box and the jumpers up near the hood. The battery appears to have a good ground. I even tried Limey's relay and that shut off one of the headlights and the horn was still quieter than I know it can be. It seems that I'm just not getting enough power. Any ideas?

Horn button completes the ground to the horn. Touch connect the purple white to ground and see it its louder. If so it is the horn button not making good contact or a bad connection to ground. Purple wire may have bad connection also. Relay kit works.

The simple way to clean that contact is to just lay on the horn for about 10 minutes :-) Seriously, it works. Basil

The horn button in the '80 cars switches the power not the ground as is the case in earlier cars. You need to touch the purple wire to volts to make the horn operate. Make sure you have good power from the fuse to the horn button.