Hi René, according to the wiring schematic the only items that are powered in the first ignition switch position (ACC) are the horns and radio. There is a single light green/white cable from ignition switch (pin 4) that splits at the fuse box (after fuse 6, 10 amps) to feed these two items with cable colours remaining light green/white. Your only option is to identify either of these two cables and splice in. I would suggest the radio feed would be the easiest/nearest.
