Sorry to butt in on this but I was reading this thread and it seemed to me
I could provide a simpler solution:-
As I understand it you have +12 for 15 seconds from the up relay
and +12 for 15 seconds from the down relay, if this is the case you can just
connect the up relay output to the “signal” wire on your antenna and link
this also to the “always live” wire through a diode (This must be able to
take full motor current- a 1N5400 is 3amp, this should be enough) NOTE the
always live connection you have at the moment should be removed. Then
connect the down relay output also to the “always live” wire - job done.
It should should then operate :- up output connects to both sending the
antenna up, both then go off and the antenna stays where it is, down relay
goes on just connected to the “always live” sends it down.
I can email a diagram if my explanation is a bit hard to follow.
1991MY Daimler(VdP)131k miles. & a sticking original antenna