w126 keyless entry installation

[Markjw]

Hi agian,
I have another problem I hope some one can help me with.
I bought a generic keyless entry kit as it had instuctions for mercedes.The problem is the wireing diagram show to break into the common wire, to wire the system up which is supposed to have permanant power. Problem is the common wire is the earth and either up has the power or down has the power depending on whether its locked or unlocked.
I have three wires from the pump Brown wire is earth, Yellow power when unlocked and Blue power when locked.
I have an early model w126 with the pump in the boot is the wireing different in the latter models.
or should I be wirering it from the door switch rather than near the pump. Any comments would be appreciated.
Thanks Mark