As Hawk suggests, the GM OE designed ammeter is actually a millivolt meter and indicates the voltage drop between the horn relay buss bar and battery junction block of the red wire installed.
One would need an aftermarket ammeter and #8 AWG wire and install ammeter between the disconnected red OE wire and the relay buss bar.
One would need an aftermarket ammeter and #8 AWG wire and install ammeter between the disconnected red OE wire and the relay buss bar.
