I have a 1993 Chevy Silverado 1500, 6 cylinder. I don't know when it started but I've noticed that the lights dim and/or my speedometer gauge will jump backwards when I hit the horn. FYI I installed a "BAD BOY" horn about 2 months ago which has a air horn type of set up. I don't know the amount of power it uses but I used the same wires that the original horn used.

You'll need a way to check altenator output. Do you get the same symptoms when other loads are added with the horn, ie: turning on the high beams or holding your foot on the brakes (Brake lamps on)?

It may require a large ampere alternator.

It's important to know how much the alternator is capable of now that you've added loads. It may be too much.

Yes get a FORD... they tend to be perfect in all aspects