Hi,

I am not sure what you mean, as far as I know for the XJS the head unit contains the amplifier, think that is true for all the XJS's regardless of age.
Were you thinking there was a separate amplifier elsewhere in the car?

The only odd thing I have heard about is the use of a common earth (not even sure what it means) that means you have to rewire the speakers if you fit a modern head unit.
I am not sure what years it applies to but I had no problems on my 1989 car when I replaced the original head unit so would think you would be OK.

Hopefully someone else will have some more concrete information.

Cheers
Mark

Hi Matt,

When you say you used a harness do you mean to adapt the Jag wiring to a format for the new head unit?

If so could you try wiring a speaker directly to the output wires on the head unit? This would prove if it is the cars wiring that is introducing a fault. On mine each wire was cut and matched to the correct wire on the unit rather than use an adaptor.

Whereabouts are you based? Probably nowhere near me 

Cheers
Mark