Honda Rescuer

My 92 Accord LX sedan auto transmission (the standard one not the fancier
version) will not shift out of 2nd gear (for a while it was staying in 3rd
gear). Reverse works fine. The dash lights show multiple lights at the same
time, usually the 4th gear indicator is on along with the one you are shifted
into. For example when first turning it on the park and 4th gear lights are
both on. Fluid is pretty new (Honda fluid). This is the third time this has
happened over the last year but the first time it has not fixed itself in a
couple of days.

I'm told it is probably the computer. Is this likely and if it is where is
it located. I called a junkyard and they will sell me one for $20.00 but I
have to dig it out myself. Is it worth the effort to try to swap the
computer out without professional on-site diagnostics to confirm what the
problem is?

Thanks for your help.