Mk4 subwoofer rca?

Do you have the original sub from factory?

And if so, do you have the external amplifier (premium audio)?

That we need to know to get the correct wiring diagrams for any substantial help.

Anyway, the original sub is not wired in the Quadlock. There are no pins for that. Either there is a separate plug in the radio unit or it is wired to said amplifier.

If you need a VIN for a car with that, I can offer one.

First of all: I don't know if the genuine Mondeo Subwoofer comes with an additional Amp or is amplified by the radio unit. And if your head unit does amplification or not. In the first case you'll need to connect your RCA signal to the connecting SW amp. RCA is just two wires. connect the one that does connect to ground to the outer wire and the other to the inner. You can use a RCA to 3.5mm adapter and just cut the 3.5mm plug.

In the latter case you could try to install an additional amplifier module with for example a TPA3116DA Amplifier. Those are available on amazon for small money.

See for example:

https://www.amazon.de/Hailege-TPA311…l/dp/B0834XJCJG

Although, you only need one of those two modules.

On aftermarket units, Speaker Ground often is just vehicle ground. If it's a high end unit, Speaker ground is shared between all the outputs, but not the chassis. Just check with a continuity tester, on which side of the plug all outputs have the same potential.

Quadlock is nothing else but a frame for up to four connectors, one for basics like power supply, one for the standard speakers, and two smaller ones for auxilliary things, for easy use combined in that frame. The pin usages of each individual connector is mostly standarized, but a sub output is not included.

Jimmy: both ways, it depends from the country or market for the car. To my knowledge, in Germany, the sub is only available with the external amplifier (premium audio). In other markets could also be wired directly to the speciallized radio with the 5th connector outside the quadlock frame.

The original sub is a two-coil speaker, connected with four wires. It is not clear if it's one pair of wires and one coil per stereo channel (left and right), or if it is a mono sum signal, sent out by two amp circuits parallel for reasons as max load or cooling issues inside the amplifier.

Okay, you have the original external amplifier. Then the signals run as follows:

1) the radio / navi unit simply sends right and left channel front and rear to the amplifier, using the 8 standard wires in the quadlock connector, as if it would do to standard speakers in the car doors. The radio / nav unit does not know anything about a sub.

2) the amplifier processes these inputs, sums up the channels for the sub and the center speaker, filters out high frequencies for the sub, and sends them to all 10 connected speakers respectively.

If you want to continue to use the original sub and center, you will have to retain the external amplifier. You simply plug the quadlock into your new radio or nav device to connect all standard speaker outputs to the amplifier as it was before. You only have one issue: The setup of the amplifier is done via CAN-Bus from the radio / nav unit as "human interface". If that "interface" is swapped, the amplifier may not be controllable, or may even refuse to start. That needs to be evaluated in "real life".

Maybe. I'm not shure. I don't have that equipment myself, my knowledge is based primarily on the wiring diagrams.

There are other users here who are more into programming issues.