I would check using a volt-ohm meter to see if your pickup has a DC Resistance reading. If they are stock pickups and checked to be working properly than I would try a few little tricks. First, if you have two or more pickups in your instrument and are of the same shape, I would put the one with the highest DC reading in the bridge position if you need more power from that position. If you play a lot of Jazz or mellow music, you may want to use the hotter pickup in the neck position.
At times the magnets in a pickup could be faulty or de-magnetized and need to be checked by a reputable repairman with equipment to check magnetic gauss (strength) polarity (north or south) and orientation (direction of magnetic field within the coil or bobbin). Sometimes magnets are put in wrong and will make the pickup sound weak and thin. If a turn of the magnet wire or coil is broken the pickup can sound thin and bright. Even though the coil is broken and you get no DC resistance, you can still get a small amount of inductance or induced current to the amplifier. If the coil is broken, the coil will have to be repaired and this will usually restore the fatness and fullness in a pickup.
Make sure there are no shorted wires or components in the circuit. A capacitor in series with the output of a signal will make a pickup sound thin and brighter. I would remove one side of a pickup to be tested from the circuit so it doesn't affect other components that could be faulty or hooked up wrong.
WRITTEN ON JUNE 12, 2015, BY