Located under the car, in the brake line running to the rear brakes. Automatic transmission. I can’t find it in my manual either. Any ideas?

 

I think it is a brake pressure differential actuator that basically detected a difference in pressure between the w brakes in the rear and if it does, it will illuminate a warning light on the dash ⚠️. They can be reconditioned, I believe.

 

It is the "anti-creep brake valve solenoid" and only found on automatic cars.
It shows up clearly on MK1 wiring diagrams but is difficult to discern on MK2 wiring diagrams. It doesn't seem to get mentioned in workshop manual texts.
If pulling up to a stop using the brakes and the throttle is at idle, the switch on the throttle and a pressure switch will trigger this valve to hold brake pressure in the rear brake lines.
This stops the car from creeping if the brake pedal is released.
Once the throttle is actuated (as from taking off from a stop) the valve is opened, pressure released and normal braking is resumed.
It's a bit gimmicky and if it doesn't work then you have to keep your foot on the brake when stopped like most automatic cars.

 

I wondered what this was, saw it - the wires are disconnected, but mine was automatic but dealer converted to manual later in life.

is that a common thing?

 

You can leave it there without any electrical connections and it will not worry you. That is what I have done in a MK1 I converted from auto to manual.
The alternate is to remove it entirely and substitute it with a bit of hydraulic line. Not really worth the effort.
Cheers

 

So Auto>Manual Conversions were common?

Only down side is it leaves 3 holes in the trunk lid

 

I have two MK2 autos and on both I have discnnected these solenoids as I found them to be unnecessary with the brakes being held on when you might not want them to be.

 

Might be nice if they were fitted to some modern SUVs when you're sitting behind them at traffic lights at night.