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1990 F150, bought it used and aftermarket radio in it didn't work, wiring looked pretty iffy. Went through all of it with a diagram and got radio working again. After a couple weeks radio starts acting funny, would turn off and on when I pulled the parking brake. Finally stopped working altogether. Today pulled the head unit and tested on battery, wouldn't light up, figured it's no good. Swapped in another head unit and it worked like a charm. Turned off power, swapped out fuse #8 with a new one (had a 20a fuse in there and wanted to get a proper 15a in) and went to check radio again. Same thing as before, no light/power on new head unit. Take it out and check it on battery, nothing. I'm confused now, has anyone had a problem like this before?
I'm going to try testing the head unit again with a speaker attatched, I'm wondering if it just killed the display? There where no blown fuses, in box or on radio. And I didn't hear/smell any blown capacitors. I'm still unsure how this happened, i didn't disconnect the negative battery terminal before pulling/replacing #8 (constant 12v?) fuse. I'm wondering if that had something to do with it? But it still wouldn't explain why the first head unit started acting funny and finally stopped working.
Guts telling me it's something with the fuse box, old head unit would cut out when I released parking brake (vibrations maybe? Loose connections?) New head unit was working fine until I turned off key and pulled the #8 fuse. Had a 20a fuse in there while testing (it was closest) and after I got it going i walked over to shop and grabbed a 15a fuse to replace.
You tested both radios out of the truck and neither work now? What brand radios?
Fuse size wouldn't have any cause for radio failure. Lose fuse/fuse panel/corrosion would have issue with power loss, but not sure why radios are dead now?
Do you have power at the radio plug now? I assume the radio has two power input(key and constant). Do you have power at both? Did you hook both to the battery when you tested it?
When you went through the wiring with the diagram did you use a meter to measure voltage and ground potential? Did you actually trace the wiring back to the source?
In the first post you said "I pulled the parking brake. Finally stopped working altogether." That sounds like wires in the wrong place, just ***** nilly "oh here is a 12v source" not paying attention to what the source is. The hot wire might be run to the dimmer wire for the dash lights thus if you have the dash lights dim you will get low voltage to your radio.
Fuse #8 is for your dome, cargo lights and warning buzzer Fuse #11 is your radio Fuse and should be 15 amps
But anyway you may need to either trace the radio wires back to the source and correct anything that is not right or abandon them altogether and start over. Physically run new 12 volt hot (through a fuse) and a new ground to the metal frame of the truck.
Byronbgs, connected aftermarket radio to wires out of harness for original radio. Did poke around with a volt meter, one was constant hot, one was switched. Thought I had the right ground. Fuse number 8 and 11 are both related to radio.
