No. You have a bad connection or faulty horn drawing too much current.
Please check if horns are a matched pair. You should typically have a high and a low note one although not relevant to issue. Check each horn individually in each location, noting that second horns connectors will have suffered corrosion whilst not in use. Note also that cables light green/white are permanently live via fuse 6, 10 amps, so you could check it's seated properly. The other purple/black ones are the switched ground connection via horn push. Check all is well there including cleaning slip ring with wheel off. Although it was obviously adequate for one horn, a dirty contact may add enough resistance to limit volts with current draw from both horns.
Although you didn't mention, if you have bought a pair of very loud after market horns they will draw extra current so a relay may be necessary and an increase in fuse size to match. The instructions should explain. This is certainly the case with air horns. Don't fit supplied relays always use quality diode protected ones.
