Need Electrical Help
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Senior User
Joined: Apr 2012
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From: Spencer Mountain, NC
Need Electrical Help
I'm in the process of adding a fuse/relay box (Escort) under the hood of my 74 F100 to power my electric fan (Volvo) and my headlight upgrade. Have already done the 3G upgrade. Am wondering what additional circuits I need to prewire for future use. One additional circuit would be for an aftermarket air conditioning I would like to install later as funds allow. What size fuse(s) and gauge wire(s) should I use for this? Also, should I power my electric choke from this box and if so what size fuse and wire gauge? Can anyone think of any additional circuits I may need? All assistance is appreciated.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Any future-proofing you may want to do comes down to YOUR needs and wants; no one else can predict that for you.
Fuse rating for the AC clutch and blower motor will depend on what you install. The aftermarket vendor should provide a recommendation.
What kind of carburetor are you running?
Fuse rating for the AC clutch and blower motor will depend on what you install. The aftermarket vendor should provide a recommendation.
What kind of carburetor are you running?
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Senior User
Joined: Apr 2012
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From: Spencer Mountain, NC
I can't think of any other circuits I will need other than the ones I listed in my original post which is why I am asking for input on any other circuits others may know of that I may need. I don't plan on an outrageous stereo or any other power hungry systems.
I'm running an Edelbrock 4bbl on a 351 Windsor ahead of an AOD transmission.
I'm running an Edelbrock 4bbl on a 351 Windsor ahead of an AOD transmission.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Gotcha. Other common things people go for are lighting loads (push bar, roll bar, etc) or electric fuel pump. Heavy-duty lighting loads will probably want to stay out of an auxiliary fuse box though and run through separate relays. I see you already listed electric fans, which is the most common.
To give you a frame of reference for the current draw of the Edelbrock choke, I run mine from the hot-in-RUN power to the (now gone) idle stop solenoid. That circuit is protected by a 7.5 amp fuse, which has never blown in the 6 years I've had it hooked up. You can measure it exactly with a multimeter to get an exact number and size the wiring off that.
To give you a frame of reference for the current draw of the Edelbrock choke, I run mine from the hot-in-RUN power to the (now gone) idle stop solenoid. That circuit is protected by a 7.5 amp fuse, which has never blown in the 6 years I've had it hooked up. You can measure it exactly with a multimeter to get an exact number and size the wiring off that.
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Senior User
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From: Spencer Mountain, NC
Thanks FMC!
You've answered my question(s). This truck is a 2wd so won't be needing auxiliary lighting with the possible exception of fog lights. I'll go ahead and prewire a circuit for them. Don't plan on an electric fuel pump. Will check Vintage Air's web site for wiring criteria for their AC units. Do you see any advantage in setting up a "hot on run" circuit through a relay for the electric choke?
You've answered my question(s). This truck is a 2wd so won't be needing auxiliary lighting with the possible exception of fog lights. I'll go ahead and prewire a circuit for them. Don't plan on an electric fuel pump. Will check Vintage Air's web site for wiring criteria for their AC units. Do you see any advantage in setting up a "hot on run" circuit through a relay for the electric choke?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
It depends on what other loads the choke shares power with. Typically an electric choke does not draw enough current to require a relay. One would use a relay if he or she wishes to add a load to a circuit that can't handle the added load current. In that case, the load current is replaced by the relay coil current (much lower). The relay contacts then bear the load current.
According to the wiring diagram I'm looking at, a '74 still has a hot-in-RUN power source to the idle stop solenoid (BLUE wire), but it does not appear to be fused in all instances. The idle stop solenoid power is the ideal location for the choke because the carburetor that would have used that is replaced by the Edelbrock. If it's not fused, you'll want to add a fuse. You certainly could use this BLUE wire to instead trigger a relay that powers the choke, but it's most likely overkill and added work. The important thing no matter what is that the power source is fused, even if all the circuit does is power a relay coil. Fuse size is a function of the current-carrying capacity of the load and the wiring itself.
Here's a rather comprehensive sticky in the Electrical forum: https://www.ford-trucks.com/forums/1...-and-type.html
According to the wiring diagram I'm looking at, a '74 still has a hot-in-RUN power source to the idle stop solenoid (BLUE wire), but it does not appear to be fused in all instances. The idle stop solenoid power is the ideal location for the choke because the carburetor that would have used that is replaced by the Edelbrock. If it's not fused, you'll want to add a fuse. You certainly could use this BLUE wire to instead trigger a relay that powers the choke, but it's most likely overkill and added work. The important thing no matter what is that the power source is fused, even if all the circuit does is power a relay coil. Fuse size is a function of the current-carrying capacity of the load and the wiring itself.
Here's a rather comprehensive sticky in the Electrical forum: https://www.ford-trucks.com/forums/1...-and-type.html
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