So I had originally posted this in the Audio/Video/Mobile Electronics section because I didn't realize this section was here... Anyways:


I am making a custom overhead console for my 89 F250 with the 7.3 diesel engine with the 130A 3g alternator upgrade. I have a very basic understanding of how 12v wiring works, but would like assistance.

On the OHC, I am planning on having a "master switch" that will provide power to the gauges and switches on it. Accessories that I have planned are: my coolant temp gauge, hour meter, manual glow plug switch, push button ignition, and 3 accessory switches (high idle, radio, and bumper fog lights). I also have a voltmeter/USB charger combo ( ) that I would like to integrate.

I purchased a 20 amp (2 prong) "fighter pilot" master switch, with a 20 amp push button ign switch. I currently have a different push button ignition, manual glow plug switch, and high idle already wired with the switches located on the dash, but would like to relocate them to the OHC when I finish it.

I guess my main question is, do I need to wire in a relay or fuses, and where should I wire them in? Also, what gauge wire should I use to properly power everything? Also, will my "master switch" and new ignition switch be big enough (amperage wise)?


I have created a rough wiring diagram (just got off of a 72 hour shift and had a couple beers, sorry if it doesn't make sense).





Thanks!

Daniel

 

Running the ignition switch(master switch) up there has me worried if it's going to supply the whole truck. I am assuming the other pushbutton "ignition switch" will be to crank it over?

It will have to be at least a 10 gauge wire, and that's a long way for the power to run all the way up and around the windshield, through the switch and then back to power the fuse box and other stuff in the truck. I think a relay is called for here.

 

I should have mentioned that I still use the key to turn everything on. The ignition cylinder doesn't work right and won't start the truck. I've replaced it once already and don't feel like going through that process again. The master switch on the OHC will just be for the console.

And yes, the push button switch will just be to crank it over.

 

Your 20 amp switch should handle everything as long as you use a relay for the foglights(normally everyone does). I would still use a 10 gauge wire to feed the switch. I am assuming you will want most everything to power on with the main ignition keyswitch, so I would run the 10 gauge feed wire to a 30 amp bosch style relay, and then run from there directly out to the starter relay/battery +. I would install a 20 or 30 amp fuse very close to the battery connection. You could mount the relay out there also, and trigger the relay with the red/green wire going to your low vacuum switch plug on the pass side fender.

Your ignition switch problem is very common, I have a 89 diesel also and it did the same thing. There is a pot metal piece broken down inside the column, it's part number 14 in the picture below.

 

Okay, got it. Thank you for your help.

And that metal piece in the column is a pain to get out, but luckily the key still works in the "key on, engine off" position. I just had to jump it at the starter solenoid the first couple of times until I got the push button in.

 

I reviewed your intended circuit diagram and it's pretty easy to follow. Appears that everything is hot-side switched, so adding relays will be a breeze. In place of each manual switch, the input from the battery positive will go to Pin 30. The output to the device (Glowplug controller, lights, etc) will be on Pin 87. Pin 86 will be to chassis ground, while Pin 85 goes to the switch in the Overhead Console to operate the device in question. It will still be hot-side switched, so the other terminal on the switch will have to be Battery Positive.

I don't know how much current each device will draw, but the bumper lights (assuming 55 watts each) is ~10A. Fuse the circuit for 15A between Relay Pin 30 and the battery positive terminal. The switch needs fused too, for 1A as it's only triggering the relay. I'll take a guess on the other items:
High Idle Solenoid: 1A (won't need a relay unless you want to put one there)
GlowPlug Controller: 10A seems like a good starting place. I don't know much about diesels though, so a more informed opinion is definitely welcome here.
Ignition Switch: Are you only triggering the START function on it? If so, 5A is more than plenty. Is you are triggering the Key ON Circuits, stick with 30A
Radio: 15A is a safe bet. The JVC KW-XR810 headunit in my RX7 has a 15A fuse on it.

A 40A Bosch-type relay and 12awg for the Master switch circuit is the correct choice. The rest can use 20A micro relays and 16awg. You might want to package everything together close to the battery using a fuse/relay panel retrofitted from another vehicle. That way, it will minimize the number of wires you need to run through the firewall. A visit to your local salvage yard might give you some ideas on where to source one from. Be sure to look at the VW Jetta Mk4 (99-05)'s fuse/relay blocks, they're rather interesting pieces