My Garmin G-III PLUS (or other) GPS shuts itself off when I hit a bump in the road (or while I am jogging with it or while I am riding with it on rough pavement on my bike,  etc.).     What can I do to fix this.

This <in my humble opinion> is a design defect in several models of Garmin GPS receivers which Garmin should correct.  As of  February 2000,  Garmin has opted to offer a "spring wafer" which fits between the batteries in the battery compartment which does correct the problem.  It is a bit "Rube Goldberg" but it does seem to get the job done.

If you will telephone Garmin at 800-800-1020 and state your problem,  they will send you the "spring wafer" device at no charge.

While you are there,  you might ask them why they allow this design defect to continue in ongoing production units instead of going ahead and adding the battery bypass capacitor (or whatever) that it would take to actually FIX the problem.

Joe Mehaffey

George Treible (Email HERE) has discovered another problem that was causing
intermittant operation of his G-III PLUS with sensitivity to vibration.  George's
information follows.

"I took the unit to my workbench and pulled out my multimeter.  Measuring
resistance across the + and - battery posts on the door should measure zero
resistance.  In fact I was measuring an open or a swinging (telephone jargon
for changing readings) high resistance short!  Looking at the positive
terminal where the negative coil spring wire winds around the post seemed to
be the likely culprit.  I gently removed the spring wire from the post with
a needle nose.  Once removed I was able to tighten the "noose" a little
using the same needle nose.  I also noticed what appeared to be a small
amount of corrosion in the groove of the positive terminal; this might be
expected on battery posts over time.  I used some WD-40 to spray it clean.

I re-attached the coil spring to the post and again measured resistance:
solid short/0 ohms.  I placed a fresh set of batts in the unit and it now
works like new!!

Lessons learned:

1) The connection between the positive battery post and the negative coil
spring is pressure fitted - it's not a soldered contact so it's susceptible
to eventual corrosion or loosening over time as was mine.

2) When I was a switchman for Ma Bell our motto was "look for the obvious."
This is a pretty obvious problem waiting to happen once you understand the
makeup of the posts on the battery door.  I'd predict a lot of III+ units
beginning to have this problem."