I had one owner just install a new RPM relay with it burning up on first power up. He sent me photos and it looks like the MOSFET driver for the WUR is cracked. Also had another owner asking about this fuse modification because it was documented on the old forum.
The RPM relay powers three things. First is the fuel pump but it also powers the heater in the WUR and the lambda relay signal wire (coil power). We have seen a few WUR short circuits inside on the heater circuit and that still does not blow the 20 amp fuel pump fuse. This may also be a reason some fuel pump fuses get overheated.
My solution is to fuse the WUR heater with a 3 amp fuse. I only fuse the WUR so if the fuse blows (your WUR shorted) it will not affect a long drive home. If I fused both the WUR and the lambda relay wire with one fuse your engine would run rich or lean on that drive home. You would know when the WUR fuse has blown when your engine takes a long time to warm-up so checking the fuse is not necessary.
The problem with this installation is they used two yellow/red wires. One powers the WUR the other the lambda relay signal. So I guessed and cut one of those yellow/red wires. Then measure the resistance of that wire (not the RPM relay side) to ground. If it reads about 20 ohms then you have the correct wire to fuse. Another check is to pull the connector off the WUR and the resistance should go to infinity.
Get a fuse socket with wires at the auto parts store and some 3 amp fuses. Install that fuse between the two yellow/red wires you cut that goes to the WUR. One end to the RPM relay wire and the other end to the wire to the WUR.
Note my photo. I guessed wrong and my first cut wire needed to be spiced back.