Many questions seem to arise concerning this seemingly simple component, such as "Where is the main power feed?' or "How do I replace this with the more modern blade type fuses?" First, there is no 'main power feed'. Here is how the wiring is on the 65/66 Mustang fuse box.
In the bottom left corner of the picture there is a contact with a black wire with a yellow stripe attached to it. There is a black/yellow wire coming from the hot side of the starter solenoid, the same terminal that the positive battery cable is attached to, which comes through the firewall, splits into three wires, one black/yellow, one black/orange and one yellow. The black/yellow wire on the fuse box is the black/yellow wire coming from the starter solenoid. This is constant power, whether the key is on, off or in the accessory position. The power is always on, thus, the term, 'Constant Power'. (insert smiley face.) You will notice that this contact has two round thingies on it. If you flip the fuse box over, you will see that one of those round thingies is the hot side of the fuse for the cigarette lighter/emergency flasher circuit, and the other is the hot side of a circuit called 'Dome'. A 65/66 Mustang does not have a dome light. This is the interior courtesy lighting which comes on when you open either door. On the other end of the Dome fuse is a green/yellow wire. This green/yellow wire goes out to the driver's side door jamb switch. On the other end of the cigarette lighter circuit is a blue/white wire. This goes out to the lighter, and splits off before it gets to the lighter and also goes to the emergency flashers, if your car has the emergency flashers. Not all 65 model Mustangs had emergency flashers.
On the middle fuse you will have two blue/red wires. One of them brings power directly from the headlight switch and the other goes to the instrument cluster back-lights. Those are the ones that come on when the headlights come on, not an alternator/generator warning light, or the oil pressure warning light.
In the top right corner, there is a black/green wire. This brings power from the ignition switch when the key is in the on or accessory position. Again, the wire is attached to a contact plate with the two round thingies. The one on the top is the hot side of the accessory fuse. There should be a wire hanging out of the front of the fuse box on that circuit which supplies keyed power to whatever accessories are plugged into that wire on the other end. The other round thingy, marked by the brown/green arrow, is the hot side of the heater fuse. There is a brown wire coming out of the other end of this fuse. If you have three speed heater fan, this wire goes out to the fan motor. If you have a two-speed, center-position/off heater fan, this wire goes to the fan switch. The fuse box of a 64 1/2 is a little different in a couple of ways. I'll address that one in another post.
So, as you see, power goes to the fuse box from three different places, the starter solenoid, the ignition switch, and, the headlight switch, and the systems that get power from one are pretty much completely isolated from all of the others. There is a little more involved in replacing this with a blade type fuse box than just removing this fuse box and sticking the new one in. The new one needs to either have a provision for isolated independent power feeds for different circuits, or, it needs to be more than one fuse box.
8 comments:
Super information. I wanted to cut my old block out and replace it with a new style one. Your write up made it a snap to use a generic 5 circuit block from the auto parts store and wire it right up correctly.
Thanks
Joe
I'm happy to hear that you found the write-up to be useful. There are a lot of advantages to the more modern style of fuse box.
I just rewired my 65 mustang with. Brand new wiring oem kit, though I thought the fuse box was a newer sale box. It's not . What's your recommendations to install a newer box? This blog is awesome! Thanks, God bless, Mike Diaz Nor- Cal.
The easiest way would be to have one fuse box with constant power, which has the black/yellow wire feeding it constant power and the emergency flashers/ cigarette lighter on one circuit, and the courtesy lights on another. You would still have a couple of slots left over on this, so you could also route the wire that supplies power to the headlight dimmer switch through the box on one slot and the taillights through another. Take a second small fuse box for the keyed power stuff and have the dark green/black wire supplying the power to the box and have the keyed power stuff. This way you would also have slots for things like a phone charger, power amps for the sound system, etc.. Whatever you wanted to run in your car. The blue/red wire for the instrument lights you would want to just put an inline fuse and skip the actual box, since this is a dedicated circuit that is simply power in/power out for the dash lights.
It's actually quite simple and not at all expensive. Just make sure that you use fuses of the same amp load as the originals. If you have something that seems to keep blowing fuses unless you go with a higher amp fuse, you have a problem somewhere and the fix is not simply use a heavier fuse.You have a short somewhere, or excessive resistance for some reason, something. The fix is to fix it.
Troubleshooting why the back up lights in my (dad's actually) 65 mustang do not work. Been reading Chiltons and 65 Ford Shop manuel, but your diagram is great. Thanks. On fuse box, no power to 2.5 interior light fuse, and one half of cig lighter. Also trying to understand how starter neutral switch is involved. I'm a novice. Any tips from my ramble appreciated.
troubleshooting back up lights on 65 Mustang. So far, found out no power to 2.5 fuse in box for inst. lights and 14 fuse on one side of cig lighter. I think power to backup lights come from starter neutral switch.
65 backuplights are down. All other fuses accesories working now. So...back to how to check 65 backup lights. Found 4 red/black wires going into Starter Neutral switch, which I believe is the power that goes back to red/black lights for two back up plus power & ground for Starter Neutral switch. Yes?
Hi again. The switch doesn't have a main power-in and fround, like some switches. It's just a wire taking power through the switch. If the switch isn't in the right position, the power stops there because it doesn't have anywhere to go. When the switch is in the right position, the power just passes through, on the red/blue wire to the starter solenoid,and, on the black/red wire to the reverse lights.
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