When you first turn the key on its normal for the fuel pump to cycle a few times then stop....without starting engine....when you then try the horn, the pump cycles everytime?
If that is the case, you should retrace where your horn relay is getting power, both on
the horn button side and the horn side. It might be tapped into the power to the fuel pump either wired that way a pinched harness shorting 2 wires together.