Car Alarms: AST 440, alarmtek, purple wire

Question
Sir:
 I'm attempting my first alarm install and keyless entry with an AST 440.  My question is probably pretty simple for you.  I was wondering if you could tell me if the '02 Toyota Tacoma is a negative or positive door pin?  This is the wire that activates the dome light, correct?  Green and green/white in front of fusebox?  I have instructions that say diode isolate each, and I have no clue what that means.  Then, hook those to the green or purple wire on the alarm, depending on polarity. Also, when reference is made to the ignition harness, is that located in the steering column?  Thank you very much for your time.  R/John

Answer
Sure John,
   For a quick tutourial, have a read on my site at
www.mrinstall.com for form and function, where to put
things, etc. Very handy infor for this. Look at the
4 runner since your's is simular. The dome light is
NEGATIVE as well as the door locks. See in you manual for
info on these, and on relay applications,
see my page at www.relayhelp.com for diagrams of each.

Thr ignition harnes is the heavier wiring coming
off of the key switch itself.

Good reading! I'll help alot!

ALARMTEK