This question is similar to can i split off another circuit from fuse box to run power to cigarette lighter?, however I want to know the mechanics of mismatching amperage when it comes to fuse tapping:
Let's say I have 2 fuses in my vehicle, a 20 and 30 amp fuse:
And I want the Cigarette lighter to have power only when the radio has power, so I connect them via a Fuse Tap:
How exactly will amperage be shared among a fuse tap?
If the amplifier asks for 25 amps, will this blow the cigarette lighter's fuse? Or will each appliance receive exactly what it asks for?
Conversely, if I connected this fuse tap and cigarette lighter instead to a lower amperage, like 10, what would happen if the cigarette lighter asked for 15 amps?
Is this safe or should I specifically look for another fuse with the same 20 amps?