Switching for additional headlamps via existing front fog lights cabling…

Hello guys, I just signed up here because I just started the project, that I want to mount additional headlights on my Forester Sf BJ 99. I want to have a switch in the interior where I can turn off the additional light permanently or if this switch is on ON, the additional headlights should only light up when the long-distance headlights are switched on… I actually thought that I could get this Bastlerei, but now I am in front of a Puzzles that I cannot understand…. I would like to use the cabling of the optional fog lights in order not to have to put a new line. I also found the corresponding connection on the left side of the steering wheel behind the dashboard. The cabling coming from the battery forks in the schematic and goes into the engine compartment into the relay box and also to the dashboard (this is thus the switch lights up when the light is switched on, but would be in m from the relay box in the engine compartment the line comes back to the dashboard and waits there to be connected with the switch to the mass … Now I thought I understood everything correctly and tested it before connecting again with the voltmeter, my results: Test from plus pole in the relay box on mass –> 12 volts …check, Well that was not understandable to me: I now close the two contacts on the dashboard via the voltmeter together I have a voltage of about 0.5 – 0.6 volts if I have switched on to II with the headlight light, if I switch down to I even 4.6 volts and at 0 I have no current flow…. Now where do these voltages come from when the two contacts are not connected at all in the relay box, or it has to come from somewhere else, because otherwise 12 volt should be measured with the contacts on the dashboard…???? Unfortunately, it doesn’t look good for this, or there is a small crack in this cable mix somewhere where there are miscurrent flows…Wouldn’t be good for the whole electrical system in this case, wouldn’t it? Thanks for your help I’m already curious what comes to mind In the appendix you’ll find the schematics