1990 nissan maxima wiring diagrams

if anyone knows where i could find a downloadable (free) copy of any engine or transmission wiring diagram for a 1990 nissan maxima (australian model) i would be very appreciative. The maxima seems to be running in fail safe mode with the gear changes being restricted to sertain speeds except when the pedal is fully on the floor. I have checked the diagnostic codes of the computer but only comes up with 'normal operation'. I have checked the wiring under the dash and the previous owner had basically mutilated the wiring. 

Any help on this topic would be appreciated as I am at witts end and don't want to be taken to the cleaners by an auto elec.

i already have the haynes manual but it doesn't go into detail on the transmission apart from throttle cable adjustments and neutral start switch test (throttle cable for previous models n/a 1989 or newer and no problems with neutral switch. the elec diargrams in the manual only cover headlights and radios but don't go into detail on the engine transmission diagrams.

i heard the chilton's version of the manual goes into more detail than the haynes so i guess i will have to chase that one up.

thanx for reading and replying as any advice is always better than no advice. :)