[HarryM1BYT]

I've just spent a good weeks worth of my odd bits of spare time on this, including lots of trips up the garden path, but the end result has certainly been well worth the effort....

I originally started with my Mk II 75, fitted with all of the separate bits of a Hi-Line system kit, including an Hardon Karmon amp and the 10x HK speaker system, including subs.

On installing a Sean DD, you disconnect 2x separate 8pin ISO plugs (a brown one and a gray one) from a combined twin 8 pin black ISO socket, behind the radio. The brown one feeds audio from the DD directly to the speakers. Its other half, the black socket is/was the output of the HK amp.

The gray 8 pin, which now feeds all of the supplies to the DD, originally was the main supply to feed the items in the boot - via its other half the black socket. Once that plug is unplugged, the HK amp will have no permanent 12v (purple/pink) and no ignition switched 12v (AKA the remote) (purple/yellow). [Edit] I also now have some sort of reception on AM, not good, but reception on the move. Previously it was complete noise, end to end.

For the 4x twisted pairs, for my initial tests, I decided to try to use network cabling. That proved itself to be NOT adequate and caused some terrible distortion. For my final install I used 0.5mm cable red and black, twisted together into wire pairs using a battery drill to put the twist in. Once installed and tested, that sounded fine.

The speaker pairs are as follows:-

Rear right - blk/grn blk/or
Front right - blk/purp blk/blu
Front left - blk/whi blk/slate
Rear left - blk/brn blk/red

For its audio input, the HK amp expects speaker level inputs, such as most standard radios would provide - including the DD. As originally wired by Rover, the input to the HK amp came directly from the radio module, mounted in the wheel well, with the HK amp mounted close to the fuel filler in the boot. The output from the HK ran to behind the radio, to the 2x 8 pin black ISO socket, then via the brown 8 pin plug to each door speaker.

To get the HK amp back into full working order is fairly simple and took around three hours of effort, in the freezing cold and the dark of my drive - once I had satisfied myself what was going on with the wiring of the original system.

Basically you need to run 4x pairs of speaker wires (8 in total) from the back of the DD, to the HK amp in the boot. Ideally these should be 4x twisted pairs, to prevent noise pick up. One pair used per channel, four channels - front left, front right, rear left, rear right.

At the front, if you happen to have a spare 8 pin brown ISO plug, they plug into the socket where the brown 8 pin ISO plug fits on the DD. The brown 8 pin is then plugged back into its original socket in the 2x 8 pin black socket. All you are doing is individually linking each colour of wire, to exactly the same colour of wire at both DD output and the HK amps input plug. The HK amp uses two plugs to connect it to the loom, the one with the fewer number of pins contains all of the speaker input wires. Be aware that EXACTLY the same colours of 8 wires is repeated on the output plug.

Now the easy bit, the power feeds need to be sorted out....

Behind the radio on the original Rover part of the loom, the gray 8 pin ISO plug has a purple/pink 12v permanent live and a purple/pink 12v switched 12v. These need to be individually linked across to the very same colours of wires, on the black twin 8pin ISO.

Basically all that was missing - was the speaker output of the DD needing to go to the HK amp in the boot, to feed it with audio. The output of the HK amp then goes to the front of the car emerging on the twin black ISO socket, so if the brown 8 pin ISO plug is plugged back in the amp will once again feed the speakers. Because th gray power feed plug has been unplugged from the twin black ISO plug to plug into the rear of the DD, you loose all feeds to items in the boot - so you link across the power between the plug and the socket (purple/pink and purple/yellow).

There - if anything seems unclear, please let me know.

Since writing this, something has occured to me....

The feed for the radio antenna amp in the back window is the Purple/yellow switched 12v. As part of trying to diagnose the poor reception of the Sean DD, I tested the purple/yellow to make sure it was live and it did seem to be. A quick check on the radio's reception last night, after getting the HK amp working, seemed to indicate that the reception was very much better than it had been previously, so I'm now wondering if when I checked that purple/yellow it might not have had a proper 12v feed going to it, that what I was seeing on the meter was just a bit of stray pick up. Until now, I have not been able to pick up Radio Aire FM - which is a fairly weak station to try to receive here anyway. After doing the HK amp circuit mods, Radio Aire FM became almost listenable. It might just have been reception conditions last night, but worth keeping in mind I think.