Modern Vespa

Wire Gr-Ne Grey/Black Fuse n.3 15A wire Rs Red - to the battery

Fuse n.3 has been blowing for the last year when I hit a hard bump. This fuse is located under the seat on the left side. Typically replacing the fuse has gotten me going right away. This last time the short must be more permanent as it keeps blowing fuses instantly. Tracing the wires out, the red wire goes directly to the battery positive and seems to be good. The Grey/Black wire goes to pin 6 of the throttle body ECU and the fuel injection loads control switch (wherever and whatever that is). I've traced the wire to the ECU. If I unplug that connection, the Grey/Black wire does not connect to ground (short out). If I plug that connection back into the ECU the Grey/Black wire does short to ground, blowing the fuse, when the key is on but not off. This has all been diagnosed with a multi-meter.

Does anyone know the breakout inside the ECU? Is this a common issue for a failing ECU? Or am I looking for another issue? The wiring diagram I have doesn't show any info on the ECU.

Unplug the injection loads relay. If you remove the pet carrier you'll find it on the left hand side. If the fuse now doesn't blow, you likely have a short somewhere in the wiring to the fuel pump, coil or injector.

Did you physically check the red wire all the way back to the battery? Sometimes the insulation gets split where it goes around a sharp metal edge.