Toyota Repair: Landcruiser electrical, neutral safety switch, electrical search

Question
Dear Mr. Ritter,

We have a 1995 Landcruiser.  We have had trouble with the check engine light always being on.  The dealership ran the diagnostic code and what came up was p1780, neutral safety switch. They replaced it, but the light continued to come on.  We went back to the dealership because the part was still under warranty.  They ran the diagnostic code again, again it was p1780, so they replaced the switch again, but the light still came back on.  Finally they said we needed to replace the computer. We got a second opinion from our private mechanic, and he also said replace the computer, so we did.  Guess what?  The light still came back on with the same code for the neutral safety switch.  So now they've taken out the new computer (to get us a refund), replaced our old one, checked the switch again, and are going to do a more thorough electrical search tomorrow.  Is there anything that you know of that it could be?  We are concerned that we won't pass smog (we are in California) with the light on, and that if something really goes wrong (like with the O2 sensor) we won't know it because the light's already on.  Any ideas or advice you have would be greatly appreciated!

Thank you,

Liz Wing

P.S.  It's taken me almost three weeks to be able to get through to ask you this question.  When I go to your page to ask questions it always says that you're maxed out, so I'm very happy to have finally gotten through!

Answer
Since the problem is not with the neutral start switch and not the computer for reasons you have already mentioned the only other cause is the wiring harness between these components.
One trouble area that can cause strange problems is in the wire harness just behind the EGR valve, if the harness is too close to the hot EGR valve it can burn the insulation and cause all kinds of weird problems so have them check for that possibility.
If you need to contact me again please do so with direct email( 3weeks is a long time but I can only answer so many questions a day) and it seems that I'm the only toyota tech here volunteering at this time, please contact me at
tedrttr@yahoo.com for further assistance.