1990 K5 Blazer Stereo Wiring Help

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Feb 8, 2012
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Tacoma, Washington
Every bit of wiring the previous owner touched on this truck is all kinds of wrong. Ever since I got the truck, the stereo turns off when I turned on the headlights, and after wiring the headlights correctly....the radio does not turn on at all. I went in yesterday to fix the wiring and get some tunes back to no avail. He wired speaker wire directly to every speaker, then tied them into the headunit harness, AND he messed up the constant 12v and ignition 12v wiring so badly that I cant discern which is which and what I am missing. I got all of the speaker wire figured out, but am still having trouble getting the head unit powered. Pictures below.

Here is what I started with:
R7mWHPS.jpg


Here is where I am running into trouble getting power:
Rnw9ejU.jpg


The speaker wire is in the background, but in the foreground there are 3 wires (from L-R), a brown wire, a black wire, and an orange wire. I assume the black wire is the ground, and I know the orange wire SHOULD be the 12v constant, and I have no idea what the brown wire does. I have traced the orange wire to the fuse box and it has not been toyed with, and the black is the ground in any GM I've installed a stereo in, so we're good with those (right?). What does the brown wire do, and why am I missing the yellow (accessory/ignition) and grey (dimmer) wire. I have tried powering on two different radio, and checked the fuses to make sure none were blown. No luck. Any tips?
 
OK, I will throw my 2 cents in from my years of experience installing radios and alarms. FIRST get a meter or at least the very least a test light or test probe.
Dark brown is almost always the parking light circuit. So if you test it, it will probably read as GROUND, but then turn on the headlight switch and it will show as 12 volt positive. This is NOT the same circuit as the gray illumination circuit wire. That gray wire actually varies in voltage when you roll the dimmer switch wheel up and down on the headlight switch. Orange is usually 12v positive, yellow or pink is usually 12v positive only with ignition switch on.

Your rear speaker wires should be a yellow and dark brown, a light blue and dark blue, and the front speakers should be a light green and dark green, and a gray and a tan. Now be careful with those gray wires because it's very easy to get the gray speaker wire confused with the illumination circuit wire. So be sure to test it wit a meter or probe. If you have any doubts still, then run new wiring. Run a ign wire and a constant 12v to the ign switch harness at the steering column, that the best way to grab a good power source. But be sure to add a fuse right where you splice in.
 
ScottyBoy said:
OK, I will throw my 2 cents in from my years of experience installing radios and alarms. FIRST get a meter or at least the very least a test light or test probe.
Dark brown is almost always the parking light circuit. So if you test it, it will probably read as GROUND, but then turn on the headlight switch and it will show as 12 volt positive. This is NOT the same circuit as the gray illumination circuit wire. That gray wire actually varies in voltage when you roll the dimmer switch wheel up and down on the headlight switch. Orange is usually 12v positive, yellow or pink is usually 12v positive only with ignition switch on.

Your rear speaker wires should be a yellow and dark brown, a light blue and dark blue, and the front speakers should be a light green and dark green, and a gray and a tan. Now be careful with those gray wires because it's very easy to get the gray speaker wire confused with the illumination circuit wire. So be sure to test it wit a meter or probe. If you have any doubts still, then run new wiring. Run a ign wire and a constant 12v to the ign switch harness at the steering column, that the best way to grab a good power source. But be sure to add a fuse right where you splice in.
Click to expand...

I have a continuity probe, but those three wires are giving me different results when I turn on the headlights. I really need a multimeter. From your post scotty, it sounds like he somehow wired the parking light circuit as the constant power source, just not sure why its not giving any power to the headunit now even with the headlights off. Oh well. Yeah, I have un-mangled the speaker wiring - hopefully they are still connected correctly. Just not sure what to do since I have no grey illumination wire.

Here is what I'm being told to do over on the K5 forum:

If you're using an aftermarket head unit, which it sounds that you are ditch all the factory wires for the stereo. They aren't worth the trouble.

Wire the speaker wires directly to the HU harness.

Look at the fuse block, you'll see a few open slots that are labeled either ING or BATT. You will need a few of the stock connections to securely tap into the fuse panel but they are easy to collect from junkyard or somebody parting out a PU, suburban or K5. Just use your multimeter to double check there is the right power at the terminal you want to use and remember to add an in line fuse to protect the wire.

For the ground there is a spade block way up on the drivers side a puller kinda behind the far left hvac vent. Or you can ground right to the dash too.
Click to expand...

So, I will just start over. I already traced a good existing IGN wire (orange), I will make my own ground on the firewall, and will run a constant wire to the fuse box. Just not sure what to do since I have no grey illumination wire. Could I trace my dimmer switch wiring to some block and then tap into that?
 
Or start at the fuse box and go from there since it hasn't been toyed with

sent from my glade air freshner
 
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