How are auto piggy back fuses connected to the fuse block.

[EmJayAre]

I am getting conflicting information on piggy back fuses that I am using in my Honda CRV and Ram Promaster 3500. I assumed that the piggy back fuse connector was a bridge between the hot and the ground bus in the fuse block and hence was independent from the fused circuit that was using that slot. In my experience the add on circuit provided by the piggy back is always on inspite of the fact that the circuit using the slot is switched by the ignition. By the same logic I can't see why it matters what amperage the circuit using that slot was before the piggy back was inserted provided you keep that fuse in its proper spot on the piggy back. Please correct me if I have this all wrong! Thanks

 

[DPG]

It's not a bridge between positive and ground. It's just picking up the live and feeding it to the spare fuse.

And yes, the circuit you feed from is irrelevant (assuming you pick one which is live at the right time of course), it is the rating of the piggy back fuse which is relevant to your new circuit.

 

[EmJayAre]

Ok, that makes sense. There is the question of 'which one is live'. The only fuse slot that I have found not on all the time is the window washer which is only on if the wipers are on. The seat heaters which come on with the ignition are on all the time through the piggy back circuit. I tried all the slots and they are all on all the time except the window washer. This should be so if the fuse block were live all the time and the circuits individually controlled by the ignition switch. I haven't had the fuse block out and I don't have a wiring diagram so I'm just trying to figure it out. Thanks for any thoughts

 

[DPG]

You might find that some of them do actually switch off after a certain time. A lot of modern cars have phased shut downs and it is not uncommon for a circuit to stay live for ten minutes (for example) after the ignition is switched off.