Trying to change the radio in my 78 F100 and need help with the wiring. Can anyone give me the breakdown of the wires that go to the radio? Maybe a wiring diagram? Need information so I don't fry the new radio!!!

 

if its like my 78, the factory radio grounds into the dash where it mounts, but there is a ground behind the instrument panel that is nice and out of the way, just put a ring terminal on some 12 gauge wire and run it back there. The factory radio, as far as I can tell, didn't have a continuous power lead because there were no presets or clock or anything. Mine just had a 2 wire plug, one for ignition switched and one for illumination on off (goes on with lights). The radio I installed was a shaft style radio with no clock, so I wired both continuous AND switched power to the radio off the single switched power lead on the factory plug. Finally, there was one last 2 wire plug that goes to the factory dash speaker, which i didn't use. I ran aftermarket wiring to the doors and put a pair of 6.5's in.

If you want continuous power, you SHOULD be able to tap the cigarette lighter. My cigarette lighter wasn't working, and when I removed the cluster and etc I learned there was like 10 feet of wire wired up to it in th dash with no less than 4 wire nuts on there running to a blown fuse in the fusebox that should have switched power on with the ignition (not continuous as the factory cig lighter was). I simply wired it into the radio switched power because I only plan on using it for a cell phone charger and for my satellite radio. If I had wanted to plug anything with more draw in there I would have used a relay as the factory fuse for the radio circuit is like 7.5 amps.

hope that helps.

 

btw, purchase and learn to use a multimeter, you'll never fry anything again.

 

The original radio used a two-wire pigtail. Blue with red stripe is dash illumination. Yellow (I do not remember the color of the stripe) is accessory power (hot when the key is in RUN or ACC). The radio grounds through its mounting bracket as stated above.

Nowadays, most modern head units require constant 12 volts, and use the switched power source as a turn-on signal. You can pull constant 12 volts from a pigtail behind the glove box; the wiring is green with a yellow stripe. You can also run your own wiring, just make sure whatever you end up using is fused.

As stated above, a multimeter will help you double check everything and determine what is powered and when.

 

Thanks for the help, fortunately I have a multimeter and use it frequently. That being said, owning and using a multimeter has never stopped me from frying anything. The biggest problem I am having is the previous owner (my cousin, deceased) installed a "newer" 1980's radio along with a booster and a few other items, a siren/pa system? so I have plugs and a rats nest under the dash and want to make sure I sort it out correctly and have everything in its correct place.

 

I am installing a SAT/iPOD/MP3 radio for now (until I can afford the retro one from LMC. This is why I want to make sure I get the wiring correct, along with adding a power outlet.

 

x3 on what they said about a multimeter. It was one of my first purchases for my old 78 F-150. It helped me solve my alternator woes in less than 10 minutes.

Well worth the 20$ I spent on it (used, but works like a champ).

Grab yourself a mutlimeter because these trucks are infamous for wiring issues because of all the grounds they have.

 

The radio power wire is Black with yellow stripe

It should have a noise suppressor as part of it.




My suggestion is to run a fused 12 gauge wire from the battery side of the starter relay, to a special power block behind the dash then set up all your extra power needs to it.

The same goes for a ground block .

 

I wouldn't. I hate it when I see an old car and someone didn't understand electricity so they just run wires off the battery for everything. Its a lot cleaner (and easier to trouble shoot) when you use the existing wiring. As long as its in good shape thats what I'd stick with. And I'd get rid of the aftermarket crap you don't want. The dash wiring on these trucks couldn't be any simpler.

 

Agreed.

No, it's not. It's yellow with a black stripe. You've misinterpreted the diagrams.

The noise suppression capacitor should be under the hood, tied off the coil or the voltage regulator. It doesn't make sense for it to be in the dash.

This makes no sense to me. All of the sheetmetal is grounded.