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Fuse sizes for lights

9423 Views 15 Replies 5 Participants Last post by  donimbimbo
There may be a more suitable forum for this question but it has to do with lights on a '68 Ford 2000. I have bought a pair of 55 watt headlights & a 35 watt rear work light. I have 20A capable switches for both. My question is what is the appropriate size fuse for each of these loads?

TexasFire :thanku:
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55 watts divided by 12 volts equals 4.58 amps. You need to allow for a surge of about 10 percent, so .4 amps plus the 4.58 means a 5 amp fuse should be good for each 55 watt light. But since you no doubt will run the two front lights from a single switch then a 10 amp would be fine, and you could go to a 15 or 20 (the max capacity of the switch). DO NOT OVERFUSE AND USE THE PROPER SIZED WIRE FOR THE LOAD.

Use the same formula to calculate the load of your rear work light.

Now for the $64 question - where exactly will you be getting the power for the switches?
- Straight off the battery? (bad idea and you can accidentally leave them on when you turn off the tractor.
- Straight off the ignition switch? (real bad idea as the ignition switch isn't built for that kind of continuous current)
- Via a relay (the best idea is the relay is picked by the switch, which is in turn powered by the ignition switch. The relay then switches current to the lights directly from the battery).
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Before you wire the lights to that aux tab let's make sure the ignition switch is rated for that much current.

Anyone know?
Sorry, I stated that wrong, I would power the light relay (if I choose to run one) from the aux tab on the switch. I have no idea what its rated for, but its a brand new aftermarket switch that I picked up from Steiners that has an on - start - aux position.

Nope, my fault. You did say you will wire straight from the battery.
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