View Full Version : 100-4 fuse size

Arch 93
11-04-2002, 08:16 PM
O.K. ...... this started as what I thought was a simple question, but I'm receiving differing answers. The question; what is the proper size fuse for the 3 speed overdrive? I'm hoping for a majority opinion.

Dave Russell
11-04-2002, 10:22 PM

Not sure what you are refering to. Do you mean the car's fuses or the overdrive specifically.

If the car, the Hundred has a 50 amp fuse for the horns & a 30 amp fuse for everything else. If you wanted a separate OD fuse, a 15 would probably do.

Note; the British fuse sizes , eg. 50, are the amps required to blow a fuse. US fuse sizes are the amps that the fuse will carry without blowing. The equivalent to a British 50 amp in US is about 30-35 amp. A british 30 amp is about 15-20 amp US.


Arch 93
11-11-2002, 08:48 PM
Hello Dave:
Thanks for your reply. What I'm getting from others is that there are two fuses; one for the horn and one for everything else, except the overdrive, which is not fused. This all started when a mechanic I had do some routine maintenance stated that the O.D. wasn't working because a fuse had blown. If the above is correct, his diagnosis is not possible. He finally found a broken wire, but I want to be sure that I don't install fuses which are too large. I gather from your reply that if I install U.S fuses, it should be a 35 amp fuse for the horn and a 20 amp fuse for everything else. Am I anywhere close to correct?
Thanks again.

Dave Russell
11-11-2002, 10:31 PM

You are correct on the above.

Many owners are not comfortable with the minimal fusing of the original cars. The entire front side light, tail light, license plate light circuit is not fused at all. These long wires to the back & front are quite vulnerable to getting grounded/shorted. Especially the license plate light which would only require a small rear end bump to cause a short, wire burning & possibly a fire. A remedy is to splice in an inline fuse holder with 15 or 20 amp fuse for the tail/side lighting. Connect the fuse in line with the red wires on the back of the headlight switch. (The blue goes to the headlights)

Also people get nervous about the un-fused fuel pump wire which can get grounded easily. Connect an inline fuse in the white fuel pump feed wire at the "A3" terminal of the fuse block. You can do the same with the OD feed wire where it connects to "A3" although most people don't fuse the OD circuit.

If all of this sounds like too much fooling around, just hope for no short circuits & carry a 1A, 10BC fire extinguisher.


Arch 93
11-12-2002, 07:47 PM
Thanks for all your help Dave. It looks like I found a project for next summer.