Fuel pump relay location and position

Car started up as normal, turned car around and started to reverse up step incline, lost a little power dipped clutch gave it some more power, put car in 1st gear and started to move forward and engine cut out and wouldn’t restart. Had a diagnostic laptop on it and the only fault present was intermittent key problem, but the mechanic was using the spare key, when I got home we used my key, no faults present! After the mechanic worked on it for a hour or so he thought there was a problem with the fuel pump he checked the pump in the tank was working via his laptop and we could hear it, but on putting the key in and cranking it over couldn’t hear anything, he used a little brake cleaner to attempt to start engine ran for a couple of seconds, he thinks it may be the engine fuel pump and have the injectors tested, after he rechecked for any faults again it came up with low fuel pressure. I spoke to another guy and he said he had the same problem and he replaced the fuel pump relay which solved the problem, he also said that it would bring up low fuel pump pressure when trying to start vehicle with this problem due to fuel pump not working, I then rang my Audi dealer to buy a new relay but needed the part number of the relay to supply the correct relay but wouldn’t advise me the location or the position of the correct relay, any help would be greatly appreciated.