someone told me that the 2 most common problems that cause an intermittent starting problem on an 89 4x4 V-6 Toyota [mine is automatic, 3VZE engine] are (1) bad battery cables, and (2) a defective park-neutral switch.

where is the park-neutal switch ??? and what does that part do, and why would it cause an intermittent starting issue?

It prevents you from starting in gear.

I'm fairly sure it's in the base of the shifter assembly (but on some vehicles it is located on the transmission where the shifter linkage attaches). If it gets loose/out of alignment it will not let you start the engine.
To find it check a service manual (see service manual sticky at top of main page).

do you have to replace the whole shifter to replace the park-neutal switch, or is the park-neutral switch just a tiny item in the park-neutral shifting assembly?

anyone have any idea what it costs to change the park-neutral switch on 89 4x4 toyota V-6 automatic?