How to connect an external amplifier to an Android head unit
Front pre-outs are the white and red RCAs on Harness A, pins A4 and A6. Rear pre-outs are the white and red RCAs on Harness C, pins C3 and C4. The amplifier turn-on lead is the blue wire on A1. Harnesses A and C ship with the unit and only get connected if you are running an amplifier.
What this gives you
Four channels of clean line level out of the head unit, so an amplifier drives the doors instead of the internal output. On a 70 Series that is the difference between losing the music at 100km/h on corrugations and still being able to hold a conversation with it on.
The same harnesses also carry a separate subwoofer output and a 5.1 centre channel, so the amplifier is not the ceiling of what the unit will feed.
Before you start
- Harness A, the front audio pre-out and AUX harness, and Harness C, the rear audio pre-out and centre channel harness. Both are supplied.
- Four RCA leads long enough to reach the amplifier, and a thin wire for the turn-on lead.
- The amplifier already mounted and its power and earth run, because the head unit end is the small half of this job.
- The battery disconnected before you pull the fascia.
Step by step
- Work out how many channels you actually need
Front only is two RCAs off Harness A. Front and rear is four, adding Harness C. A subwoofer is a separate output again on A16 and does not use any of these four.
- Connect the front pre-outs
On Harness A, A4 is the front left pre-out and carries a white RCA plug. A6 is the front right and carries a red plug. Run those two to the front input pair on the amplifier.
- Connect the rear pre-outs
On Harness C, C3 is the rear left pre-out with a white plug and C4 is the rear right with a red plug. Run those to the rear input pair. Skip this harness entirely if the amplifier is only doing the front.
- Run the turn-on lead
A1 on Harness A is the external amplifier control and the wire is blue. It goes to the remote or turn-on terminal on the amplifier. Without it the amplifier either never wakes up or stays on and flattens the battery overnight.
- Leave the speaker wires alone unless the amplifier is doing that speaker
The 16 pin main plug still carries the four factory speaker pairs. A speaker driven by the amplifier should not also be wired to the head unit output.
- Set the gains with the head unit volume high, not low
Bring the head unit up to about three quarters of full volume on a track you know, then raise the amplifier gain until just before it distorts. Setting gain against a quiet source is how people end up clipping every time they turn it up.
- Check balance and fader before you blame the wiring
If one side or one end is missing after the install, check balance and fader on the head unit first. It is a faster check than pulling the dash apart.
If it does not work
- Amplifier never powers up: check the blue wire on A1 is on the amplifier remote terminal, not on a permanent supply.
- Sound from one side only: check balance on the head unit, then check the white and red RCAs are not swapped or half seated.
- A whine that rises with engine speed: that is an earth path problem, not the pre-outs. Take the amplifier earth to a bare chassis point rather than a factory bolt with paint under it.
- No sound at all from the amplifier: confirm the head unit still plays through its own speakers, which separates a head unit problem from an amplifier one.
Worth knowing
Harness A also carries an AUX audio input on A5 and A3, white and red, so a second source can go in without touching the amplifier wiring.
Related guides
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