Thread: After market head unit p38

What model Range Rover do you have?
Some only had a basic sound system & used a garden variety Eurovox head unit.

It has the Harman Kardon setup with 3 speakers and amps in each door + Sub in the back. Its a late 99 4.6

Think you need to have a look around the internet. Seem to remember seeing something about needing some kind of adaptor to connect to a non standard head unit. Not sure why thisd was though. Also that there are differences between the two head units that were fitted and this will impact on what you need. This is though from memory so may be wrong or incorrectly applied.

I fitted one to my P38, I had to track down which original wires powered up the amps and I then hooked them up to Ignition, chopped the original plug slightly and it fitted to the loom I had, I also got the radio antena adaptor from Jaycar.

Cheers and hope that helps

I am getting there slowly and have found out that there is a grey and black wire on the original radio wiring that is the power feed for the Amps. This can be connected to the blue, electric aerial power lead from an after market head unit and switches on the amps with the head unit. The speaker outputs need to be attenuated before reaching the amps (whatever that means). My understanding is the speaker output from the after market unit will already be amplified so needs to be Un-amplified. Without the attenuator this will cause interference and high volumes with low head unit volume. There is a circuit diagram on another board that describes how to make the attenuator involving 5 separate resistors. I have e-mailed this to an electronics wiz I know and he says its unnecessarily complicated and my understanding from his reply is a 580 ohm resistor across each of the speaker wire + and - will work. I am now awaiting confirmation from him.
Any views on that?

Wikki, An attenuator is effectively the opposite of an amplifier, though the two work by different methods. While an amplifier provides gain, an attenuator provides loss,

Have just got the info back on where the resistor needs to go. It goes inline on the + pos wire of each speaker feed between head unit and amp. The Ohms resistance is not critical and might need to be different for different powered head units. The advice was to start with a 330 ohm 1w resistor, then if still to loud increase the resistance to 580 ohms or more. Sounds very easy and better still cheap.

if your amps need an 'attenuated' signal just use the RCA signal outputs on the deck instead of the speaker connections. it will give you the right signal, all you will need to do is buy some rca plugs from jaycar or similar and solder leads onto them. assuming you buy a 'good' head unit it should have front, rear and sub rca's.

My unit only has RCA`s for fronts not rears so this is not an option for me. As the 4 Resistors are only 10c each from Dick Smith Its almost free.