Installed EMG 57/66 into and Ibanez PS 10-2. Plugged all wires as shown in the instructions. Had to install a longer stereo jack plug. Now I only get bridge pickup. Cannot get neck pickup to work.

i believe you need a 1/4" unbalance plug for the amps input. Basically a guitar cord. If I am understanding the question. ? or if you want to know the actual "input jack",Maybe it is lacking or missing? than that would be a "1/4" unbalanced input jack". good luck, I hope this helps.

it you're replacing a passive pickups, you'll need to find a place for the battery (that'll be the hard part)
EMG specifies 25k pots, you might need those
plus a 'stereo' 1/4" output jack to switch the battery off when you unplug the guitar.
if you're not using the EMG routing bus (connector block thingie) yo want to wire it something like this

Some hopefully easy fixes : Input jack could be the problem, or connection from the amp to the speaker. Does the speaker hum a bit with the volume up almost all of the way without anything plugged into the unit? If not, check the connection from speaker to amp.

If it does hum slightly when u crank the volume, check your input jack -- it might be jacked up (pardon the pun) and you can fix that easily by soldering in a new one.

Not hard - just wire up one pickup and leave the other one alone. The active pickup will have wires that say "output + and - " - just use those to connect to the same place you would attach a passive pickup. Also, an active pickup will need space for a battery (9v). I weould consult EMG pickup installation for diagrams. You will also probably need to replace the guitar jack with a TRS, where the ring is a "killswitch" for the battery when the guitar is disconnected.

Try this diagram set: http://www.emgpickups.com/skin/frontend/emg-2013/default/pdfs/2-tw-2v-1t-only.pdf

If the sound you when plugging in the headphones is coming from the main speaker, it is just the interupt contacts on the headphones are making or breaking contacts. This can be a good sign if there is volume to it.

Make sure the plugs you are using are the right length for jacks in the Ibanez as there are 5 lengths in use.. If this just developed, the length issue is not a concern. If the jacks are loose, snug them down, it may be a faulty ground relying on the chassis contact with the jack.. It may be a broken wire. It can also be a dirty switch contact or dirty level control, especially the standby switch. make sure they are clean with some contact cleaner. Make sure your level is turned up too,

If you have effects, or a preamp on the guitar, make sure they have fresh batteries or good power connections and are not on mute.

The input cable MUST be a TS (unbalanced cable) to turn the unit on. The sleeve of the input cable is what connects the battery. If you use a TRS cable at the input it likely will not turn on. A TRS cable has a tip, ring AND sleeve like many 1/4 inch stereo cables.

The batteries are turned on by the guitar cable being plugged in. If they run down with the cable out, the contact of the "ring" part of the jack is shorting. The "ring" contact is shorted to the sleeve contact to turn on the battery. If you leave your guitar cable in for a day or two, the batteries will run down.

The half-way cord is the clue. Read up on unbalanced and balanced lines and TRS connectors.
One of these requires TRS connections and the signal is being carried on the RING of the TIP-RING-SLEEVE connector. Plugging in half-way the TIP touches the ring pickup contact. The emgs one MAY use TRS type cables and there may be a reason the signal and hot of these are reversed. If I could find schematics on all this equipment I could unravel the exact cause. You could make an adapter with a Stereo 1/4 inch plug and a 1/4 inch jack by wiring it to swap the tip and ring between them to use for connecting to the emgs guitar. ALSO verify you are using the SAME type guitar cable for both.OFTEN a TRS cable will NOT turn on the electronics when plugged into a guitar. Use an unbalanced instrument cable unless you have the XLR type output. Use of an adapter from the XLR type cable into the Boss will usually not work.

Realize that when you plug into the one jack it disconnects the fingerboard pickup from the mix.

DO NOT USE "stereo" cables as it is intended to use TWO MONO cables, one for each side of the stereo.

IF you plug into the one jack that will connect to the bridge pickup, it will disconnect the fingerboard pickup from the mix BUT leave the fingerboard on its own jack.
That same jack will have BOTH fingerboard and bridge pickups IF the second jack (bridge) is not plugged into.

This is according to the schematic. If you find that yours works backwards, then either the schematic is wrong OR your guitar pickups may be electrically swapped.

The fact that the pedal works in the on /ff is not a complete exhoneration.

Due to certain possible failures the pedal can still be at fault. Test the resistance of the switch and leakage resistance.

The two inputs may have different electrical characteristics where one would tolerate a partially defective switch and the other would not.

Use an ohmmeter to test the pedal before drawing conclusion.