This post is to help anyone who has a device in the trunk that has a high impedance input, for example an audio amplifier. The car in my example is a 2004 V70. It should work on any P2 Volvo from 00 to 04. I'm not sure about 05 to 07 models. IMPORTANT: THIS CAN NOT BE USED AS A POWER SUPPLY, IT CAN'T SUPPORT HIGH AMPERE!
After installing my Subwoofer using its high level input connected to the rear speakers, I realised the amplifier would only turn on if 12V was applied to the remote turn on input. At first I just used crocodile wires to connect them but for a permanent solution I consulted the internet. It turns out there is a fuse (#16) in the rear fuse box that supplies 12V when the ignition is on. For some reason, this didn't work for me so instead I took the fuse box off the wall and looked behind:
![Electrical wiring Automotive tire Audio equipment Gas Cable]()
I tested all the connections until I found one that works. Turns out, it's the yellow one at the very top next to the red one. All you have to do is connect a another wire to it as shown:
1: make sure the battery is disconnected, then cut the wire and don't forget to put the shrink tube on before soldering:
![Circuit component Electricity Audio equipment Computer hardware Electrical wiring]()
2: solder all the wires:
![Circuit component Electronic component Computer hardware Electronic engineering Electrical wiring]()
3: slide the shrink tube over the soldered area and heat it with a cigarette lighter or heat gun:
![Electrical wiring Audio equipment Electronic engineering Cable Computer hardware]()
4: cover the area with electrical tape:
![Circuit component Audio equipment Electronic engineering Cable Electricity]()
5: put the fuse box back while making sure you don't clamp the wire behind.
I hope this helps someone in the same situation as me. I have already tested my wiring and it all seems to be working fine. If you don't know what the resistance of your turn on switch is, you could always solder in a 10k resistor in series to make sure you don't overload the 20 year old wiring.
After installing my Subwoofer using its high level input connected to the rear speakers, I realised the amplifier would only turn on if 12V was applied to the remote turn on input. At first I just used crocodile wires to connect them but for a permanent solution I consulted the internet. It turns out there is a fuse (#16) in the rear fuse box that supplies 12V when the ignition is on. For some reason, this didn't work for me so instead I took the fuse box off the wall and looked behind:
I tested all the connections until I found one that works. Turns out, it's the yellow one at the very top next to the red one. All you have to do is connect a another wire to it as shown:
1: make sure the battery is disconnected, then cut the wire and don't forget to put the shrink tube on before soldering:
2: solder all the wires:
3: slide the shrink tube over the soldered area and heat it with a cigarette lighter or heat gun:
4: cover the area with electrical tape:
5: put the fuse box back while making sure you don't clamp the wire behind.
I hope this helps someone in the same situation as me. I have already tested my wiring and it all seems to be working fine. If you don't know what the resistance of your turn on switch is, you could always solder in a 10k resistor in series to make sure you don't overload the 20 year old wiring.
