My friend recently got into guitars and bought a Les Paul Special II, he asked me to change out his pickups for some Seymour Duncans he bought and I told him I had virtually zero experience with wiring but he decided he'd let me tackle it.

Anyway, long story short, I installed them, adjusted them, etc. but now the volume is super low. like, I have to crank the amp up quite a bit more than I used to just to get a decent sound out of it. It sounds a lot better than the normal pickups it came with, but I'm confused about the volume thing. I know these pickups have diagrams for guitars with 4 pots, and this guitar only has one volume and one tone control for both pickups. Could that be an issue?

I'm pretty lost, lol.
Les Paul Player!
How far are the strings from the pickups when fretted at the 12th fret?
go to the SD site and get the proper wiring diagram.
Fact: Bears eat beats. Bears beats Battlestar Galactica.
The pickup is probably out of phase. This happens with some seymour duncan pickups. It happened to me in the past. The hot wire needs to be switched with the ground wire. Sometimes even the wiring diagrams are wrong although they are usually right.
My Gear:

Fender Strat w/Duncans
Hand Built(by me) guitar w/Duncans
Ibanez RG321MH
Bugera V22
Peavey Vyper 30 Watt
Xotic BB Preamp
MXR Carbon Copy Delay
Digitech Hardwire Chromatic Tuner
Fender T-Bucket Acoustic
Digitech Bad Monkey