Ok guys, we're working on a 73 F100 with a 460 and c6. As far as electrical add ons, there is an MSD ignition module, a jensen 300 watt amp, a sony A/M F/M CD deck, and factory A/C.
I put this stereo and amp in it over 6 months ago and everything worked fine until yesterday. When I pulled my headlight switch all the out side lights came on, and none of the interior lights worked. I replaced the fuse which was burned in two, pulled the headlight switch and immediately blew the fuse again.
I started unpluging different components trying to locate the short. When I finaly got over to the stereo and unplugged it, the truck quit blowing fuses. I carefully checked the harness for the stereo, and found a bad place in the insulation. I taped it up, replaced the fuse.....everything worked again right up until I plugged in the stereo. The stereo plays great when it's plugged in, I just can't keep a fuse in the fuse box for the dash panel lights.
The wire that is supposed to be hot all the time on the stereo is spliced in to the big yellow wire on the ignition switch. I cut the plug off of my factory stereo for hot with the key on and ground and spliced that plug in to my stereo to make it a plug in deal. It worked perfectly fine like that for about 6 months.
The only thing that has been changed recently is the addition of the factory A/C which has nothing to do with the lights except for the light that goes to the control panel. Other recent additions include a factory cigarette lighter, an ash tray light, and the glove box light. All of the recent light additions were pirated from a 73 XLT in the bone yard and were direct plug ins. Any one have any ideas on where to look for the problem?
Thanks in advance for any help,
Mike

 

Obviously it's something to do with the stereo. You have an earlier model, so I am not positive of the wire color, but on all the 75-up models, the instrument lights all have a lightblue/red feeding them. The original radio harness should have this wire included in it, since the original radio had a light inside it. Your new radio also may have a place for this wire, to dim the display at night when the lights are turned on.

Take the stereo out, replace the fuse, and see if you can find the wire that is hot with the lights on at the stereo plug.

 

Dave,
I completely rewired the stereo and it cured my problem. I hooked the memory wire (hot all the time) to the big yellow wire on the ignition switch that is also hot all the time. I wired the wire that is supposed to be hot in the accessory position, to a black wire with a green stripe on the ignition switch which was only hot when the key was on or in the accessory position. There is a bolt that holds the bracket under the dash that supports the back of the stereo. I put a ring connector on my ground wire and run that bolt through it as a way of grounding the stereo to the cab. When I replaced the fuse for the dash panel lights this time, everything worked like it should. That blue wire with a red stripe that your talking about goes to just about everything in my truck as far as interior lights and accessories.
I just recently added a cigarette lighter, an ash tray light, and glove box light to that blue wire with the red stripe. Would it be possible with the new additions as far as lights coupled with the aftermarket stereo was just more than that wire could carry? Like I say, once I got the stereo off of that circuit everything worked like it should. If you have any further information, I would like to know just for future reference.
Thank you for your response and all your help so far,
Mike

 

Is this a cigarette lighter light, or does it run the cigarette lighter? If it runs the cigarette lighter, that is probably too much for the circuit.

 

Dave, I got the stuff from a 73 XLT to add the actual cigarette lighter, and ash tray light. So actualy....I added both. I also added a glove box light to the same circuit. Looks like I may have over done it.
Thank you for the response and information. I'll know better next time. I think I may be lucky that I didn't burn my truck down. I guess what they say is true....The good lord takes care of those too ignorant to take care of themselves.