Fuse Change for Horn Circuit.

Well here's some info for you I gathered from work computer this morning. The NEC lists various types, closest for automotive wiring I would imagine SIS which is used for control power and switchboard wiring. All other conductors are solid in the table, NFPA 70 latest revision (2020) listed below. There are many factors that will play into the calculation as these are base values. Temperature, number of conductors, raceway/conduit install, etc. These are for free air which will likely be used in most automotive applications.



Here is some further info for base ampacities from NEMA WC 73-2000 (R2018).

 

Use this calculator, it allows you to set the % voltage drop you will accept. Can also select 12V or 13.8V.

https://www.wirebarn.com/Wire-Calculator-_ep_41.html
I installed dual bass tone PIAA horns (2.7A each per specs) and one thing I can tell you is that tiny horn wiring is 22awg at best and possibly smaller. Toyota doesn’t want to spend money on copper and voltage drop be damned. With a 6-8ft run I’m sure I’m over a 5% voltage drop, one day I will put on some ear plugs and measure it with my DMM.
The wire isn’t going to melt for the short time you put up to 10A or so on it but you will have a hella voltage drop and therefore your horn won’t be as loud as it could be with adequate wiring.

 

Thanks Guys.

I have put the project on hold. Life has intervened to change plans.

The refrigerator died. Just purchased a new unit. It'll be delivered on 1/11. Meanwhile, everything that was in the frig/freezer has been moved to the unheated garage. The garage is a giant frig/freezer this time of year. Temperature is hovering around 28*F.....with a downward trend. Fortunately, we didn't lose any food.

Yeah, I'm thinking I may need to run 18-20 awg wire to feed the 4 tone system. 4 PIAA horns, each at 2.7 A. Prolly have to dig back to the fuse box to run the wire.