Jag XK8 seat motor

[Vinpetrol]

I have a Jag XK8 2001 . When I took it home a couple years ago the drivers seat won’t go back or forward. It has a module under the seat and this is clicking when I work the switch either way . I’ve checked the plug with 2 wires going to the motor .
When I push the switch one way one of the wires is live . When I push the switch the other way the other wire isn’t live .
The little black box beside the motor has 2 wires in it . Does it look like they should both be going live when the switch is pushed either forward or back . ?
What is the little black box for ?
Should I try a live feed down both these wires to see if the motor moves ? Do you think one wire should be an earth , but if that’s the case how does it change direction ?

 

[Gecko]

It doesn't look like a relay to me. Looks like a noise suppressor (maybe).
If you put your meter onto continuity (beep) position, I'd guess terminals 1 - 2 and 3 - 4 are connected (at all times)

Are you sure it is 'this' box that is clicking?

Found a diagram that shows the UP and DOWN relays are separate

You definitely need to bookmark this page, if you haven't already:

JagRepair.com - Jaguar Repair Information Resource

Jaguar Auto Repair Directory

www.jagrepair.com

Adding to what I've said above
There are two relays, but they work together.
In the 'normal' state, both relays ground both sides of the motor. When you select a direction, the corresponding relay toggles, providing 12V to one side of the motor (while the "other" relay provides the ground path).

So - first test - can you check (when nothing is powered) that both sides of the motor are connected to ground? (my suspicion is the ground wire is floating)

Do you have seat heaters and do they work? (they share the ground connection, so would be an easy test).

Aaaaannnd .... I just reread your post - your problem is the forward/back motor, not the up/down (correct?)

That complicates things - I'd still start by checking the ground connections. Disconnecting the motor and feeding it directly with Gnd/12V one way and then the other would be a good confidence check.
If you have the "5-motor seats", the diagram will look like this: