Toyota Repair: 89 pick up starting problem, amp fuses, continuity check

Question
Hello, i recently bought an 89 toyota 4x4 pick up.  at the time of purchase
the seller told me that it had a bad starter because sometimes it would not
start.  so the first thing i did was have a new starter put it.  but it continued
to have problems intermittently.  when i turn the key the lights and radio turn
on, but the engine does not turn, and there  is NO clicking sound.  sometimes
if i just wait a while and try it again it starts up. usually however, nothing
happens, no turning of the engine.  I have to jump start it.  i have had the
battery replaced, the alternator checked, and even batter wires replaced.  
whenever i take it to the mechanic or the dealer, they can't find anything
wrong with it, and they are never able to reproduce the problem (of course).  i
really hope you are able to give me some insight.  thank you.

frustrated

Answer
Dominic,
Was there an engine swap at any time?
First thing to do is check the ground (-) wire from
battery to frame/body ground, make sure it is tight fit and clean.
Find ground strap from frame/body to engine, make sure its
tight and clean, if its broken replace it, There might not be one
if engine was replaced or removed.
Make sure both battery clamps are clean, tight, and in good shape.
Follow the positive strap backwards from the battery, make sure all
connections are tight and clean. Check the connections on the
50 and 100 amp fuses, do a continuity check on these wires while
wiggling them.

Let me know.

Tim.
ToyDoc