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Car Stereos/02 Trailblazer OS-2C-BOSE wire location


QUESTION: I have the os-2c-bose for my 02 Trailblazer with bose and on star and the radio died out of no where. Now I pulled the relay that came hooked up to the adapter harness (OS-2C-BOSE) thinking it was the cause. I lost the relay and cant for the life of me remember how to re-wire the harness back to the radio. My HU is a Kenwood KDC-BT358U. All im trying to fix is the deck right now I just need to know where the wires go because I cant get the unit to turn on anymore. I can rig it and get power by putting negative,constant, and switch together so I know its not a fuse or connection. So either I cant wire it right or my amp blew.

Thank You,

ANSWER: Hi Ryan,

I'm not quite clear on what's going on with your installation.  Are you still  using the OS-2C-BOSE, but just missing the relay?

If it helps, here's a link to the installation manual for the interface:

If I'm understanding correctly, the head unit will power up when you hardwire the accessory power input to the constant power feed, but not when connected through the adapter?  The relay is necessary to make the adapter work properly--it's used to boost the current capacity of the module's accessory power output.  Because there's no key-switched power wire in the adapter harness, the module generates an accessory power source for you, but the module's output can't handle too much current.  PAC uses the module output to trigger the relay, which then connects the new head unit's accessory input to the constant power source (fused in the vehicle at 15 amps).  

If the problem is that you're missing the relay, you can purchase a replacement at any auto parts or car electronics store.  It's just a standard Bosch-type SPDT relay.

If you have a multimeter handy, you can test the voltage of the module's accessory power output (red wire in pin #1 of the 18-pin harness, as shown in the manual I linked above).  With the key on, you should be getting 12 volts on this wire.  If not, the module's accessory output circuit may have failed.

Hope this helps; if not, feel free to send a follow-up question with more detail about your problem.



---------- FOLLOW-UP ----------

QUESTION: OK so far I have the manual you gave to me. If I'm correct my switch (red) goes to 86 from PAC and switch (red) to 30 from HU to relay. My ground (black) goes to 85 from pac and my constant (yellow) goes to 87 from PAC to relay. Now there is from PAC the remote and amp trigger. Do they go to same color on HU because everything I'm being told is to reverse wire them and I can't understand why. If it is my accessory output that has gone bad where is this located... in the rear fuse console. Can I use a 40amp relay to just test connections and if I can get it to work get the right relay. The PAC comes with 2 yellow and black so I assume one to head wire and other for relay but if you look at manual it says for both switch (red) wires to use same relay connection and on the top of manual it shows for the Switch (red) wire to go to #30 on relay connection. Wasn't a very upfront manual because it doesn't even explain which wire to connect the PACs amp trigger wire too. And yes I am still going to use the os-2c-bose. Hope this helps you get a better picture because I am lost in this one. I really do appreciate your time.
Thank You

Hi Ryan,

First of all, I'll go over how the relay works so you'll have a better understanding of what you're doing when you're wiring it up.  

On a relay, the 85 and 86 terminals are called the "coil" terminals.  Their function is to activate the relay.  If there's voltage on one terminal and ground on the other, the relay will activate.  Once the voltage or ground is removed, the relay turns off again.  So the red accessory wire going from the PAC piece to terminal 86 is just activating the relay.  If it's working, you should hear/feel the relay click when it turns on, and again when it turns off.

A relay is really just a switch.  When it's turned on, it connects terminal 30 to terminal 87.  When it's off, the connection is broken.  So when the relay activates, the head unit's red accessory wire (connected to 30) is connected to the yellow constant power wire at 87.  

This is all you need for your head unit to power on--a ground connection, voltage on the yellow constant power wire, and voltage on the red accessory power wire.  The amp trigger and remote wires have a function that we'll go over, but they aren't necessary to make the head unit switch on.  So if your problem is that the head unit isn't turning on at all, then your troubleshooting should start with those three wires: red, yellow, and black.  

The picture on the PAC web site isn't very clear.  I see that the manual diagram appears to show two wires coming out of each of the pin positions for these three connections:  one for the relay, and one for the head unit.  That's correct for the black and yellow wires, but I don't think it's correct for the red wire.  In other words, the black and yellow pins at the PAC module should each have two wires:  one connected to the relay, and one to the head unit.  However, the red pin should have one wire connected to the relay at terminal 86, while the red accessory wire from the head unit should be connected to terminal 30.  There shouldn't be a direct connection of the red wire between the head unit and the PAC module--the only connection should be through the relay.

When I mentioned the possibility of the accessory output having failed, I was talking about the accessory wire coming from the PAC module.  There isn't any radio accessory output in the vehicle, because the Trailblazer's factory radio is controlled by the data bus system.  That's one of the reasons you need an adapter module like this in the first place.  If the relay is wired correctly but isn't clicking on and off with the key, or if you aren't finding voltage on the PAC's red wire with a multimeter, then it might mean the PAC's accessory output is bad.  

Now, as for the amp trigger wire: you should only be making connections to the 18-pin PAC harness.  The 16-pin harness (the one with the vehicle plugs) shouldn't be altered at all. So the blue/white wire in the 18-pin harness is the only connection you need to make (you can ignore the blue "antenna" wire in the 18-pin harness).  The blue/white PAC amp trigger wire should be connected to the blue/white "P.Cont" wire in the Kenwood harness.  This is the connection that makes the PAC module activate the factory Bose amplifier, but it's not required for the Kenwood head unit to power up.  In other words, if this wire isn't properly connected (but the rest of the wires are) then your head unit would power up, but you wouldn't hear any sound.

Finally, if you're still having power problems, be sure to check the vehicle's radio fuse.  It's a 15-amp (blue) fuse in position #41 in the fuse box under the rear seat.  The Bose amplifier also has its own fuse, 20-amp (yellow) in position #11; however, a blown fuse in this location wouldn't affect the head unit power.

Hope this helps!


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