I have a pair of SP2XT speakers. The woofer works fine but the horn doesn't work on either cabinet. I checked the driver and saw no damage.

Your woofers are probably blown. To check plug a 1/4 inch or speakon into the speaker cabinet with the two bare wires exposed on the opposite end and touch with a 9volt flat battery if the driver doesn't move ir sound it's blown

In Peavey cabinets, the lower woofer is always Yellow + and Blue - and the horn is always Red + and Black -. On the middle 15" the remaining two wires would be White + and Blue -

High side speaker input jack defective, as they are switch also and if you plug the wire from the amp in full range and no hf sound but connecting directly to the bi-amp hi does, then your female 1/4 plug at crossover is defective for sure.

They used what is a called a "Miter Fold Machine" to cut the cabinet from one long piece to something you can fold up that looks like your cabinet.

The short answer is they did not mean them to be serviced. However the two methods you can use to get into it are,
1- locate the corner where the ends came together and try work them apart,

2- get a sber saw (mistakenly called jig saws these days) to cut a window in the back of the cabinet. Save the insert and attach it to larger piece that fits over the hole- you will change the tuning of the speaker slightly, but the larger panel with the cutout attached will bring the volume back close to original and the overlapping edges of the patch cover should be sealed to the cabinet. Paint them flat black like the originals and they will look better when done.

Check the crossover network for cracked solder joints, specially pay attention to the female1/4 jacks as they are very tricky since they are switches also, you might be surprised...

Open the unit and remove one wire from one of the woofer terminals and using an ohmmeter check the resistance between the terminals. It probably should be between 6 and 16 ohms... they don't give the specs on the speaker... if it is very high or infinite resistance, the voice coil is blown and you be re-coning or buying new speaker. These are close in speakers and intended for a small room for studio listening while mixing. If the speaker is OK, then the bass amp in the cabinet has a failure... pray, as that is cheaper to repair than a speaker.

Usually the colors you will find are red and black pair and yellow and white... USUALLY the red/blk pair go to the tweeter horn with red going to the + lead of the horn drivers. Usually the yellow/white pair go to the woofer with the white going to the + lead of the woofer in Peavey speakers... HOWEVER you never know if someone has rewired the cabinet so going by colors is NOT the best way to go... This should have the "soundgard" circuit in it and the lead that goes throught the lamp and resistor that is NOT connected to the inout jack is the TWEETER + lead. The pair that connects to the inout jack DIRECTELY is the woofer leads and the TIP connection of a 1/4 inch jack is the + woofer lead. Verifying these connections is the best method.

This is a bi-amped speaker. That means it has a separate power amplifier driving the bass woofer and treble horn. They have a low-level electronic crossover to separate the frequencies to the appropriate speaker. The electronic crossover is the least likely to fail... so you need to do a test:
You will need to open the unit and using an ohmmeter check if the woofer speaker voice coil is open or has continuity...It should be around 6 to 16 ohms. If it is above that, the speaker itself is blown and will have to be replaced. If the speaker has continuity, then the bass amp has failed and will require repairing by person that is adept at electronic repair. Before opening the unit you MIGHT be able to diagnose whether the speaker itself is blown by seeing if the woofer generates a thump when power is turned on or off. If it does, then likely the speaker is OK and the problem is the amp, otherwise the tests above need to be done. Usually these plastic cabinets are held together with seveal scrwes from the back. Some are in :deep "wells" and will require a very long shaft phillips screwdriver... and they often are long screws that wear one out unscrewing them. A genlte pry after removing the screws will separate the back and the front.

does the cab have a horn like the one in the photo if it does then you must think again.

you must try to get a replacement crossover or get a speaker geek to fix it for you its not so hard you can get the burnt out components fro radio shack / maplin so on. most of the blown components will show damage or smell like they are burnt because thats what they are.

the cross over plays a very important job in the fact that it filters of the top frequencies so you only get subs on the bottom 12's bass / mid on the top 12's and hi frequencies on the horn.

you will loose all the quality if you go direct and could easily blow things up especially the horn.

this speaker cab looks like a Kenny i had and when working then they are fantastic. i blow one of the sub 12's and the cross over survived so unplug the speakers and test them 1 by one with a little power from an amp and a small amp that does not matter if it gets damaged

Best to have it reconed ! The speakers need to be matched pair.

If you are using these for music instrument(s) make sure they are intended for that use. Home stereo speakers won;t take the power that music instrument speakers are designed for by a factor of say four.

If these are mis-applied, don't waste money repairing, but buy instrument grade cabinets.