Hi JAY,

On 03-Apr-04, JAY EMRIE wrote to GEORGE WHITE:


 JE> GW>
 JE>> one). Two types of flashers now. Then for vehicles towing a
 JE>> trailer with turn signal lights an even different flasher was
 JE>> needed - one that would operate properly (flashes per sec) both
 JE>> with and with out the trailer - commonly called a HEAVY DUTY
 JE>> flasher here. My 89 Ford van used this method as did most
 JE>> vehicles I came in contact with. I haven't looked at my 92 Ford
 JE>> Crown Vic nor my 92 Chevy PU - which I use to tow a trailer. The
 JE>> PU came with a towing package which may have included a flasher
 JE>> that takes care of the trailer. The trailer has two bulbs in each
 JE>> the left and right tail light.

 JE> GW>The towing package was probably no more than two relays to
 JE> operate the GW>lamps (one for each side) and a current sense relay
 JE> in the feed to GW>sense the trailer lamp current. These days this
 JE> can be just a winding GW>round a reed relay, the trailer lamp
 JE> flasher inicator is driven by GW>this relay. Probably set up to
 JE> indicate "good" if a lamp works, and if GW>there are two it
 JE> probably won't tell if one of the pair fails.

 JE> Since the trailer light feed is a tap off from the rear tail,stop
 JE> and turn signal light of the tow vehicle (in other words in
 JE> parallel) how would a relay get into this picture? I've wired many
 JE> vehicles to supply the trailer lights - there is no way the
 JE> trailer lights can operate a second relay. ONLY the increased
 JE> current in the lamp circuits (tow vehicle and trailer combined)
 JE> causes the flasher to work. Sadly, I have never taken a Heavy duty
 JE> flasher apart to see how they work, simply because I have never
 JE> had one to fail and I wasn't about to take a good one apart. :-)

If it is a dedicated flasher the rules are different. I was just
talking about the kits I've installed in my family's cars when we
fitted a tow hitch. They just tapped into the rear stop, tail and turn
circuits too. However the turn signals went into a unit that also had
a power feed (ideally ignition switched but it didn't need to be) and
an earth connection (needed for the relays).

George

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