I had a previous post looking for assistance with my radio not working when the key is in the “accessory” position. I forgot to mention the radio is new and was bought from a dealer and is an exact match to the old one.

The radio operates perfectly when the key is in “run”.

The accessory wire is providing a full 12v to the radio when the key is turned but, yet, no radio.

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While researching this problem, I obtained these radio wiring diagrams from a dealer so I thought I would post them in the hopes they could provide assistance to others.

They are for my 04 Blazer Zr2.

The radio has me stumped. My only guess is the radio receives a signal from the computer to operate when the key is in “run” but doesn’t receive this when it is in “accessory” and is tied to it being new.

 

It’s not worth pulling your hair out, do it the easy way:

Rewire the plug so the 12v accessory hot feeds into the radio ignition hot wire.



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The OEM radio harness has two power wires: (orange-always hot) dark green (Hot in Accessory or Run). It has others for illumination, etc but these are for primary controls.

My green wire originates directly from the driver door fuse panel and is fed by the ignition wire being fused at this location. It reads 12v when the key is switched to acc or run at this location (door fuse panel).

At the radio and using a digital multimeter, this green wire shows 12v when key in run AND 12v when key in acc. However, the radio only works at “key in run” position even though both provide 12v to the radio.

So, both provide adequate power but radio only turns on if the key is in run.

Unreal

Thank you for replying and a Merry Christmas

 

Take it out and test it on a bench. If both acc and ign hots are working through the same wire, and your multimeter shows 12v in ign and acc, the only thing that could be preventing it from working would be a switched ground.
I always thought these were switched on the hot side

 

I have tested everything and have been working on this for numerous hours.

Everything works even in RAP but the darn radio. My last guess was a ground and your switched ground makes sense. Thanks for pointing me in a direction I had not thought of.

 

When I turn my key forward to run, the wire reads 12v and radio functions.

When I turn my key back to lock position, the radio turns off and wire reads 0.

Finally, when I turn it back toward me one “click” to accessory, the wire reads 12v but radio doesn’t work.

You are correct in they are one wire.

Could this set up still involve a switched ground?

 

Did you get it figured out?

 

No, but thanks for checking.

In talking with people and calling dealerships, It sounds like the radio needs to be programmed to the Vin number on my truck.

However, that does not explain why it will come on with the vehicle running but not in the accessory position or under RAP. It is the same wire coming into the radio and the voltage measures the same from both switched locations/RAP and the grounds test fine.

I will be contacting a person in a neighboring town who is very good with these type of problems. As soon as I find something out I will post my findings in the hopes it can help somebody else in the future.

Happy New Year

 

Well, my local “guru” is stumped. However, I found a post in our Forum from 2012 of the exact same issue directly encountered after a total power loss. However, the post was never expanded.

But, in playing around with my radio, it did start displaying a “Cal Err” message just like the aforementioned post. Everyone has a different interpretation of this with a common theme being a programming issue. I have called 5 dealers and visited 2; all are very uncertain what to do and none had heard of this”Cal Err”.

 

Perhaps you could try PM’ing the poster from the older thread? I know it’s a long run, but you could get lucky