I just changed my bridge pickup into a D Activator (DiMarzio) from DD HB-102, but where did I go wrong?

Although my soldering skills are, well, I don't have any, never even soldered before, I think I managed to connect the pickup. But the sound I get out of it is much weaker than it from the neck pup.
It's just two humbuckers, no coil-taps, two tones and a volume.
Sounds like the pickup is too low trying raising it the bridge pickup is usally as close to the strings as possible without interferncing from hitting it while playing.
I've been imitated so well I've heard people copy my mistakes. -Jimi Hendrix
Perhaps you accidentally wired in parallel
RG351DX - Bridge Dragonfire Screamer, Mid+Neck Fender Hot Noiseless
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AMT E1 > Joyo AC Tone > Dan'o EQ > Shimverb > Digidelay
Nope, I is not a matter of the pup height.

How could I have done that parallel installation? I checked the diagrams from Dimarzio and SD, also the ones telling which cablecolour is which in them.
Then I installed them the way the older were - so does it mean that the ground cable switched places with the hot cable?
Yeah, got is solved. Had to change ground and hot wire - duncan designeds have a different colourcoding on their wires...

But now, as I was playing a bit louder with my band, there's this little highpitched sound if I'm not playing anything and touch the strings.
Grounding sucks, probably?
Could be grounding or a cold solder joint. More than likely if the noise stops once you hit the strings it has not been ground properly. If you followed the diagram correctly I doubt it is a lack of you not grounding it, but rather bad soldering. Trust me, I practiced on a beginner guitar when I was soldering, I am still not that great at it, but I am getting better.
Gibson LP traditional and DC standard, PRS S2 Custom 24, Schecter Banshee 7
EVH 5153, Mesa DR Tremoverb combo 2-2x12's
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Think it might be a bad soldering, yeah. I'm not sure whether it was a good idea to solder the ground wire to a metal screw where all the other groundings were and then the bare wire to a back of a potentiometer. but I think it also made the noise only when I was playing facing the amp, so have to live with it for a while now.