51 12 volt conversion
Elder User
Joined: Mar 2003
Posts: 788
Likes: 1
From: Hendersonville, TN
Maybe a bit more info on the rest of your setup? Changed other stuff? (12V ignition coil, starter, battery, bulbs, etc?). The pump should have a wire that's hot with the ignition on, run through a 2-wire oil pressure switch at minimum, or a late-model's fuel pump relay, which ties into the oil pressure switch. The alternator's wire should be about a 12 gauge and run directly to the battery hot side(either the cable or at the starter solenoid) and should have fusible link a bit larger than the alternator's rated current output.
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
Buddy,
A 12 Gauge wire for the alternator will work okay as long as it doesn't put out more than about 60-70 Amps. Personally, I prefer 10 gauge and if the alternator happens to be a 100 AMP, consider using 8 gauge wire. This is not a place to skimp on wire size as bigger is always better. Also be careful if you are running an ammeter as most only register 60 Amps. A 100 amp alternator should NOT be run through an ammeter anyway if that's what you have. Use a voltmeter instead. Being from the old school, I've never worried much about tieing an electric fuel pump in through an oil pressure gauge...and use either an inline 20 amp fuse or run the power from a 12 volt relay that is fused. Just mount it as close to the tank as you can and feed 12 volts to it from a source that's hot only when the switch is in the "on" position. If the pump has a metal housing it will ground to the frame or you can run a ground wire to any good ground. Run at least a 12-14 gauge wire to the relay and a 14 gauge off the relay to the pump. If you wire it direct without a relay, use 12 gauge all the way back.
Vern
A 12 Gauge wire for the alternator will work okay as long as it doesn't put out more than about 60-70 Amps. Personally, I prefer 10 gauge and if the alternator happens to be a 100 AMP, consider using 8 gauge wire. This is not a place to skimp on wire size as bigger is always better. Also be careful if you are running an ammeter as most only register 60 Amps. A 100 amp alternator should NOT be run through an ammeter anyway if that's what you have. Use a voltmeter instead. Being from the old school, I've never worried much about tieing an electric fuel pump in through an oil pressure gauge...and use either an inline 20 amp fuse or run the power from a 12 volt relay that is fused. Just mount it as close to the tank as you can and feed 12 volts to it from a source that's hot only when the switch is in the "on" position. If the pump has a metal housing it will ground to the frame or you can run a ground wire to any good ground. Run at least a 12-14 gauge wire to the relay and a 14 gauge off the relay to the pump. If you wire it direct without a relay, use 12 gauge all the way back.
Vern
Elder User
Joined: Mar 2003
Posts: 788
Likes: 1
From: Hendersonville, TN
Good points GNW, on the factory Ford trucks, higher output alternators always use a voltmeter instead of an ammeter for these reasons. I always preferred voltmeters anyway. I had a Chevelle that I put a Holley electric pump on, and ran it direct to a switched 12V, and it was fine, but sometimes annoying when switching the key on to work on it. It is cool though to simply switch the ignition to "on" for a second before starting and know your carb is full.
