ah.. in that case... I'm not 100% sure so best to be asking Stu really, but..

Presumably you have a second ignition amplifier that has to be wired in?
It's quite likely that it will use the normal trigger output on 25 to trigger one amp and 26 (which isn't used on a standard P8 setup) to trigger the second one, with the ground return signal from 24 going to both.
At the ignition amp end the trigger signal (from 25 or 26) connects to pin 6 of the amp and the ground signal return (from 24) connects to pin 3 of the amp.

But please confirm with Stu or someone who has this setup, that it is pin 26 that is used for the second ignition amp trigger.