On Fri, 9 Oct 2015 10:53:50 -0400, Stormin Mormon
wrote:

I've got a Chevrolet van that doesn't run when
it's wet out. Earlier mechanic had done some
diagnosis and looking around in the wiring
harness that goes from the engine to the computer.

Makes me wonder if there is water getting in
to the wiring harness, and that's what makes
it not run when it's wet.

What's a good way to seal this, to keep water
out? Duck tape? Scotch 33 electrical?
First things first - good spark plug wires. You have the potential
for 60,000 volts there - that voltage will leak theough anything that
is not perfectly waterproof. New wires with silicone dialectric past
in the coil boots and the plug boots (and distributor boots if it
still has a distributer)
12 volt wires don't leak appreciably through insulation that is wet or
dry. If they are going to short wet, they will short dry too.
Low voltage (sensor) connections are working on 0-5 volts - so again,
moisture won't short them. If anything, take the connectors apart and
clean them. A bit of dialectric grease hear usually won't do any harm
either and will keep moisture from getting in and corroding
connections. Moisture on low voltage stuff is more likely to cause
corrosion and open circuits than shorts. The new plugs we've been
telling you to put in for the last 2 years will help too as the wide
gap and rounded electrodes of worn plugs requires a lot higher voltage
to jump the gap. A good sharp well gapped plug will hold your
secondary voltage down around 45000 volts - a lot easier to keep in
your wires. Also make sure the cap, if a distributor model, and / or
the coil towers are prisinely clean..

Thes steps will make even a 6 volt chrysler flathead start with a
water hose pointed at it.