Some car stereos have "floating ground" speaker outputs, with electrically active negative wires. Installing high-power stereos like this in a car with factory-installed speakers that are wired so that all negative speaker terminals return to the dash on one or two common ground wires requires you to wire through a floating ground adaptor. This will cut power in half, but save you from having to rewire your speakers.
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Things you need
- Stereo wiring instructions
- Floating-ground adaptor
- Wire nuts
- Wire stripper or cutting pliers
- AA battery
- Car-specific speaker wiring harness adaptor
Plug the speaker wiring harness adaptor into the wiring harness behind your dash.
Trace a path from each wire in the harness adaptor through the plug to the speaker wiring of your car, to determine which positive wires go to which speakers. Use the harness adaptor's instructions or the car's own wiring code as a guide.
Press the bare wire end designated as the negative or "-" speaker return against the negative end of your AA battery, and briefly touch the left and then the right positive speaker wires against the positive end of the battery: Each time, you should hear a scratching sound through a speaker. This will confirm which wire goes to which speaker.
Connect the floating-ground adaptor to the front speaker outputs of the stereo if you have just front speakers. If you have just rear speakers, connect the adaptor to the rear speaker outputs.
Twist together the stereo speaker output wires with the floating ground adaptor input wires using wire nuts sized correctly for 18 gauge wire. Attach left negative to left negative, left positive, marked +, to left positive, and the right-side wires accordingly. Attach the left side positive of the floating ground adaptor output to the left side speaker positive wire, the right side positive of the adaptor output to the right speaker positive wire, and the ground wire of the adaptor output to the speaker negative common wire. .
Follow Steps 1, 2, and 3 of Section 1. If all speakers share one ground, it requires use of a separate fader, not covered here. Otherwise, go to the following step.
If the two front speakers share one ground and the two rear speakers share the other ground, connect the front stereo outputs to one floating ground adaptor and the adaptor's outputs to the front speakers as in Section 1, Step 4.
Connect the rear stereo outputs to the other floating ground adaptor's inputs and the adaptor's outputs to the rear speakers as in Section 1, Step 4.
Tips and warnings
- Speaker "ground" is the same as "negative," marked "-"
- Many car stereo shops stock floating ground adaptors. They also are commonly available from a variety of online sources. The same applies to buying a speaker wiring harness adaptor.
- A speaker wiring harness adaptor has on one end a plug that inserts into your car's specific speaker harness socket and on the other end wires with bare ends.
- Do not common-ground a floating ground stereo without an adaptor: that will destroy either the output transistors or your speakers.
- Do not twist the wire nuts on too tightly, or you will break the wire. Twist them on until the wire ends completely disappear into the nuts, then test them with a light tug.
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