Do you mean that you connected a stereo audio system in the truck?
Try removing the -ve battery cable from the battery post and then connecting a DMM (digital multimeter) set to read DC Amps between the chassis earth and the -ve battery terminal and check what the current measurement is. The setup would be chassis earth > meter lead > through meter > other meter lead > -ve battery post
Normally the meter would show approx 50-75mA.
If it is more than this you have to start pulling the fuses one by one and check what happens to the meter reading after each has been removed and then replaced (so you don't confuse which fuse goes where)
When the meter reading drops to normal you will know because of which fuse it is, the circuit which is causing the problem,
If you don't have a DMM then you could do the same by removing the -ve battery cable, removing a fuse and then see if you get a spark when you replace the cable. If there is a spark, remove the cable, replace the fuse and move onto the next fuse etc.
Do all this with the engine OFF.
If you did install a new stereo system, maybe start with the fuses for it first.