I'm a bit of a newbie in the automotive wiring department, and I need some help.

I am building a custom overhead console for my 1979 F250, and it will house 4 powered toggle switches, front and rear map reading lights, and glowshift tinted tach and vacuum gauges.

Now the first question: I will be putting in a fuse block under the dash so each thing has its own in-line fuse. Will I need to have 8 positive wires for each port on the fuse block?

Second question: After I run the 8 hot wires up the front A pillar, will I need to run the negative wires back to the fuse block? Or can I just have them ground out to the roof of the cab?

Third: Toggle switches don't need a ground wire going to them, but the thing they are activating do (which I know). Does that mean that I would only have to run 4 negative wires to the fuse block instead of 8?


Thanks
Jameson

 

Yes, you can have a "common" ground. Remember tho, that all your body parts will need to be grounded also.....so long as all the body parts have a connection back to the battery.

 

You do not need negative wires going to the switches. There is a negative all around you, it's anything metal in the truck.

You also do not need negative wires to the switches because they are only switching hot wires. You will have a hot wire coming from a fuse, going into the switch, and a switched hot wire leaving the switch. The only reason you may need a negative wire going to the switch is if the switch is lighted. In that case it will have a extra wire on the switch, but all these extra little ground wires do nothing but give a ground to the internal light in the switch. You can take all these little grounds if you have them, tie them all together and then bolt them to a ground in your console.

The lights for your gauges, and your tach will also need a ground to work. And I am assuming you will be using screws to bolt this console to the metal roof? If so, I would put a terminal somehow under one of the screws that is going through the roof to hold the console in, and run a wire from that to a common point where you can tie all these little grounds together to run the tach and all the lights in the console. No need to run ground wires up the pillar.

You also do not need to run negative wires to the fuse block you are adding for the same reason. Whatever you are running can be grounded wherever it's located to the metal body of the truck.

What are you going to run with these switches? How many amps does each thing take if you know?

 

I only have one filled, a double throw for a police siren. All the others will be running cab lights, fog lights, and a rear cargo flood light. Don't have any of the lights yet, so I don't know what the amp draw is.

What gauge would you recommend? Another guy on this forum used 14 gauge, but he said it was overkill. My plan was to use 18 gauge


Thanks
Jameson

 

If you are going to run foglamps off one of the switches, 18 gauge is going to be too small. I don't know how much the siren draws, but you will be limited by the 18 gauge wire. The length of the wires will limit you also. I am not sure where you were planning to get power for your added fuse box, but the factory wiring is pretty small and can barely handle the truck's original wiring.

What I would do for ease of hook-up, and pretty much all the power you will ever need, is to mount your aux fuse box under the hood near the battery, and also mount relays to your circuits. This will let you run very very small wires and switches up the pillar to the console, and will make it easy to run the heavier wires to your foglamps, siren etc under the hood. The new factory trucks have this system as a option, they are called "upfitter switches".

So what I would do is decide if you want any of your switched added accessories to be turned on and off with the keyswitch of the truck, or powered all the time. If you want both, i would tap into the original fuse box with a very small wire to something that turns on and off with the ignition, and tie another small wire to a always hot point in the fuse box. I would run these wires up to the console.

The first place the switched power would run is to the tach. It would then also run to the switches that would be switched on and off with the key.

The constant power can run to the switches that you want to work all the time.

If you can find a small cable that has 5 or 6 different colored wires inside it, this would be ideal to hook to the output of the different switches, and then run this cable through the firewall, and over to your new relays The small colored wires would go from each switch to each relay, and the switches would just turn the relays on and off.

 

I would buy relays like this.
Surplus Center - 12 VDC SPDT 40 AMP RELAY WITH SOCKET BASE