From:Dave Hennessey
Subject:RE: Fuse Date:Fri Aug 24 09:57:09 2012
Response to:17729

There was a fuse in the late-1958 and 1959 Model 165, but it wasn't where you'd expect it to be. Look at the wiring diagram for the Model 165 over in the How-To-Restore Chapter 66. The fuse is in the green wire coming from the regulator "F" (field) terminal to the generator. The late-1958 and 1959 Model 165 were the only ones to use this fuse.

The purpose, I think, was to protect the battery from overcharging should the generator field circuit become shorted to ground. Causes of this would include a bad voltage regulator, frayed wiring, or internally shorted field coils. The voltage regulator functions by constantly opening and closing the contact points inside the regulator. The contact points actually connect the generator field circuit to ground. When the generator output increases, the contact points open. As the output drops, they close again. This happens 50 to 200 times every second.

A faulty regulator or other cause of a grounded field would cause the generator to constantly give full output, damaging it, the battery, the wiring, etc.

I really don't know what size the fuse was. The service manual says that a normal field circuit should draw two amps when shorted during testing, so I'm guessing a fuse somewhere between 3 and 5 amps would be appropriate.

People often put a fuse in one of the battery wires to protect the battery and wiring from a frayed wire grounding to the bike's frame or similar situation. I'm guessing the maximum load on the battery from ignition, headlight, taillight and stoplight might be 10 amps, so perhaps a 20 amp fuse would be appropriate here.

Given the limited service most of our bikes experience, if your bike's electrical system is in good shape, you shouldn't need a fuse at all.


What are the pros and cons of installing a fuse on a 54 165 ? What amp would be appropriate ?