Outer Limits 4x4 Board

Hi Guys
I have just fitted a rebuilt 3L to my 1990 Hilux, all is working great except it is now killing batteries????
Something is now staying on (drawing current) when the ignition is off. Is is enough to kill a Z704wd overnight (completly flat)
I am runnning out of ideas.
The battery leads spark when the key is off.

put an ammeter in series with the battery, and with the ignition off, start pulling out fuses and watch the meter. when the current disappears, you have found the bad circuit. if it still draws current with all fuses pulled, then the problem is in the starter motor (unlikely) or in an accessory that is wired straight from the battery. keep disconnecting until you find the circuit.

try your alternator first then all your aftermarket accesories