What Frank said. Use a 20 amp fuse. Hook it up and blast it with the
car running at cruising speed for 10 seconds (which will seem long) or
however long you plan to use it. If the fuse blows, install the
relay.
Reasoning:
If the horn draws 18 and the wire can handle the load, it will be
fine. If the wire can't properly handle the load, it will get warm.
Normally wire has very low resistance. As wire is overloaded it gets
hot and the resistance increases. If your wire increases in
resistance enough to draw that extra 2 Amps then it will blow the
fuse. Also, if the fuse blows, check for smoke and/or burned wires.
This is sometimes referred to as "the smoke test".
A stock horn probably draws less than 5 Amps. If you have a stock
charging system an 18 Amp horn will probably dim the headlight a
little. This might be a good thing as you will get a visual flashing
light effect to go with your audible train horn.
|