Glow Plug Relay Seat Leon 1M TDI

Hi, I have a Seat Leon 1M TDI with the MB ARL engine. It also has a coolant pre-heater, which is original equipment. I'm now looking for the relay that controls it, and I've checked under the water tank cover in the driver's footwell, under the trim, etc., but I can't find it. Can anyone tell me where it is located? Thanks.

Above the brake fluid reservoir, on the splash guard, there's a small box where both relays are located. They are relay number 53 (small setting) and relay number 100 (large setting).