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Re: [TR] TR3A wire harness (rear) question

To: <triumphs@autox.team.net>
Subject: Re: [TR] TR3A wire harness (rear) question
From: "Randall" <TR3driver@ca.rr.com>
Date: Sat, 11 Jun 2011 14:50:44 -0700
> Problem is when I turn the light switch on, the Ammeter jumps 
> to 30+ and the rear lights are dim and the wires red hot

So, in addition to the short, you've got the ammeter wired backwards.

> The diagrams I have indicated that the two tail lamps are in 
> series with 2 red leads that tie each together, correct?

That's called "in parallel", since each fixture is connected between the red
wire and ground.  But yes, the red wire goes to three fixtures, to the dim
(tail) filament at each corner and to the license plate light in the center.

>  I haven't seen any diagrams that indicate 2 green/purple leads 
> to the right tail lamp, should these be twisted and go to one 
> connection, or is one of them not used?

Check any of the later factory diagrams, they all show the two GP wires.
"Twisting" is not acceptable practice, IMO, instead they need to be soldered
or crimped or both.  And yes, the two wires both go to the same bullet,
which connects to the bright (brake) filament.  However there is no power on
that wire until you step on the brakes with the ignition on, so it's not the
problem.

If you don't have a factory diagram, go to
http://tinyurl.com/286jzzu
and download "Practical Hints 6th Edition.pdf".  The wiring diagram is on
page 49, and the rest of the book is something that every TR3A owner should
have.  (It's basically the factory owner's manual for a later TR3A.)

> I also 
> didn't remember any grounds on those lamps when I pulled the 
> old ones out, and I didn't ground these other, should I start there? 

There weren't any ground wires originally, but I recommend adding them.  I
made up a ground harness from 16 AWG black insulated wire, with bullets for
each fixture (all 5 of them) and a ring terminal for the RH fuel tank
mounting bolt (plus a star lockwasher).  Wouldn't hurt to ground the fuel
sender while you're at it.

However, I don't think any of this is the actual immediate problem!  What
you are looking for is a short between the red circuit and ground.  Since
the rear lights come on (dimly), most likely the short is somewhere else,
like at the front lights.  My next step would be to disconnect the red
circuit to both front lights at the junction behind the horns on each side.
Then if the ammeter still hits the peg when you turn on the switch, you can
try disconnecting at the rear lights (all 3 of them).

-- Randall  

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