I know things... A lot of things.
Join Date: Feb 2015
Motorcycle: GSXR 750 K4
Re: Voltage regulator fried .
+1 to what Bill said above. When you disconnect the ECU, you don't just remove this one part, but break a lot of other connections, both immediately, through the disconnection of the ECU couplers, as well as indirectly, since the ECU controls power to certain devices (such as the fuel pump). You should therefore determine, as far as possible, that the ECU is indeed the root of the problem before replacing it. Note that the K6/7 service manual I have seems to have the fuses wrong in the wiring diagram. Fuse #4 is labeled as the ignition fuse, but is obviously the signal fuse. The ignition fuse is fuse #3 with the O/Y wire coming out of it, which soon enters into the unlabeled box next to the fuse box, (call it the sidestand relay or ignition interlock box) and emerges O/B, then turns O/W at the engine stop switch, and from there powers: the ignition coils, the cooling fan relay, the fuel pump relay, the ECU and the immobilizer (if equipped).
Try disconnecting all of them, except for the ECU and see if the fuse still blows.