You'll see a resistance to ground.  Fuzzy memory says that it's about 5 amps
per brake coil so if you have 2 axles and all 4 wheels have brakes, that'll be
20 amps max.  12.5 volts/20 amps = 0.6 ohms.  Unless you have a very good
meter and low resistance test leads, that will look like essentially a short,
reading anywhere from zero to one ohm.

It'll probably be easier to just hook a lamp in series with a 12 volt source
and probe the socket with that.  The lamp should light at something less than
full brilliance when you hit the brake pin.

The other part of troubleshooting is to analyze what changed.  If they were
working when you put the trailer up but aren't now (and assuming someone
didn't sabotage it while in storage) then the range of possible problems is
very limited.  Even more limited by the controller having power.  Probably
limited to the connector.

You can test the wiring to the connector by connecting a bulb between the
brake pin and ground.  See if the green light on the controller lights.
Manually actuate the controller and see if the bulb lights.

If you have power to the truck connector then there are only a couple of
possibilities that would cause total discontinuity on the trailer.  Connector
corrosion or a wire pulled loose from the connector or cut.  If you find
continuity on the trailer connector from the brake pin to ground then you'll
want to look at the truck.  If it is open then I'd first examine the trailer
cord for damage and then disassemble the connector to look for a wire pulled
loose or corroded.

You didn't say where you are but if you have to put it in winter storage then
you probably have snow and salt.  I'd be taking a good hard look at the
truck's connector.  See if any of the blades have turned green or otherwise
have cruft on 'em.  Clean and degrease the connector with brake cleaner. Get
an ink-type eraser (abrasive) and shine 'em up good.  Apply some waterproof
grease to the contacts to prevent future problems.  Any old non-graphite and
non-moly grease will work - no need for high dollar dielectric grease.

My first money would be on truck connector corrosion, something you might be
able to temporarily clear by inserting and removing the connector several
times.  If that clears the problem, give the connectors a good spit-shine at
the first opportunity.

John

--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
If stupidity hurt then there'd be Aspirin in the salt shakers.

You should read some nominal amount of resistance.  You are reading
through coils.  If the resistance is really high or an open then you
have a bad wire.  All the coils wouldn't go bad at one time.  The fact
that your light is out, indicates an open wire.

Here's Dexter PDF for lots of brake info:

http://dexteraxle.com/i/u/1080235/f/6-8K_Service_Manual_3-08/Electric_Brakes_2-08.pdf

7" brake magnets are 3.9 Ohms; 10"-12" magnets are 3.2 Ohms.

Pete

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Use a small file or screwdriver and clean all of the contacts on both
connectors. Crud gets in them over the winter and its not at all surprising
to lose a connection point. Heck, I've had this happen during the summer
just before pulling out for trip. Scrape the contacts and you are usually
good to go.