Wire Gauge VS Amp Load

Here’s a quick and dirty guide as to what wire size you should use on your bike. There are a lot of factors involved in wire size, such as amp load and length, but the following is just fine for almost every bike out there. Don’t forget if you use switches to look at the amp rating on them. I’ve also run across 40 amp breakers and the bike was wired in 16 gauge. In a case like that the wiring stands a good chance of being toast before the breaker pops. With the exception of electrical pigs like dressers with all kinds of gadgets on them, A main breaker should be no more than 30 amps and on really stripped down choppers and bobbers, with kick start only, I sometimes use just a 15 amp breaker. Using a fuse, especially a little glass one is totally bullshit. If your are stuck on the side of the road because you ran out of fuses, you deserve to sit there in my book.

Back in the early days, right up until like the early 80’s, 14 gauge wire was the norm. Then as wiring harnesses got more complicated and you had to fit more wire in the same space 16 gauge is the standard. I think some of the wire size has gotten smaller because the manufacturer is cutting costs, although there is small weight advantage reading up on airplane wiring there was also an electrical advantage, although that might be due to the fact airplanes use 24 volt systems.  Personally I like 14 gauge for main connections, like battery to ignition switch and the power lead coming from the generator or alternator,  and 16 gauge for the rest.

  • 22 gauge       5 amp
  • 20 gauge       8 amp
  • 18 gauge       10 amp
  • 16 gauge       20 amp
  • 14 gauge       40 amp
  • 12 gauge       100 amp
  • 6 gauge         150 amp
  • 4 gauge         > 200 amp

Some average loads

  • head light               8 amp
  • tail light                   2 amp
  • ignition system     2 amp
  • horn                          4 amp
  • starter                      100 amp