electical question 71 f100
Cargo Master
Joined: Oct 2011
Posts: 2,246
Likes: 303
From: Kenner,La.
Amp draw
I do not know how much it will take. Do yourself and the truck’s electrical system a big favor and add a high amp power relay to carry the load.
My favorite relay is the metal ones from NAPA that can carry over 100 amps, they look like a solenoid. I have one on my 67 XL & 68 Ranger.
My favorite relay is the metal ones from NAPA that can carry over 100 amps, they look like a solenoid. I have one on my 67 XL & 68 Ranger.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
Depends how it is wired.
In principle, all amp draws should not exceed 80 percent of the alternator output.
But it depends what is on at the same time. For example, would ya really be running a winch, stereo at full blast, with the AC on?
In principle, all amp draws should not exceed 80 percent of the alternator output.
But it depends what is on at the same time. For example, would ya really be running a winch, stereo at full blast, with the AC on?
Fleet Mechanic
Joined: May 2001
Posts: 1,396
Likes: 4
From: Cupertino
Luv, here are the current-carrying capacities for wiring. I can't find the gauge of the ignition switch wire. I think 16 ga is a good bet. The guys will chime in here.
Under no circumstances should you exceed the wire limit.
https://www.powerstream.com/Wire_Size.htm
Under no circumstances should you exceed the wire limit.
https://www.powerstream.com/Wire_Size.htm
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5th Wheeling
Joined: Feb 2012
Posts: 45
Likes: 0
Blew 20 amp preinstalled fuse to ac/heat that was on same feed as fuel pump. heat on high defrost. so blower was on high, heat was on and ac with fuel pump. i changed 20 amp to 30amp because i figured ac/heater draw was the culprit. AC/heat is electronic control.
May take fuel pump and go direct to battery, have toggle switch in anyway and its not like you would forget to turn off ..you cant hear it from 20 ft away
Logistics Pro
Joined: Mar 2009
Posts: 4,853
Likes: 607
From: Minnesota
That fuel pump should be on a relay to the batt with an activation wire from the ignition. That way the pump will only be on when the switch is in the start/run positions!
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Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
1st, I'll ask if you've done the 3G upgrade or not. The 45 or 60 amp factory alternator couldn't keep up with everything. Especially with the headlamps on.
Now once that is done I think you have to worry more about the wiring than the switch. As Cougarjohn referenced. 2X Fuel pump should be on a relay. Stereo amp(s). As well as an aftermarket A/C motor.
Now once that is done I think you have to worry more about the wiring than the switch. As Cougarjohn referenced. 2X Fuel pump should be on a relay. Stereo amp(s). As well as an aftermarket A/C motor.
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Fleet Mechanic
Joined: May 2001
Posts: 1,396
Likes: 4
From: Cupertino
Luv, you haven't solved any problem by replacing a 20 amp fuse with a 30 amp. You have increased the power dissipated in the wiring by 125%. You are risking an engine or dashboard fire.
Either replace the wire to handle 30 amps (see the chart I put up) or put in proper relays.
The fuse is there to protect the wire, not what you put on it.
Either replace the wire to handle 30 amps (see the chart I put up) or put in proper relays.
The fuse is there to protect the wire, not what you put on it.
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Sam's1967
1967 - 1972 F-100 & Larger F-Series Trucks
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Nov 16, 2015 05:44 PM