[TR] TR250 LED tail light problem

[Roger Elliott]

HI Randall,

Thanks for the information and the tests.

I just want to check something on the tests since my electrical trouble 
shooting ability is very limited.

This section is also done with the lights on, right?:

To check for grounding issues, I suggest running a wire to the negative 
battery terminal or negative starter cable, so you can connect the 
ground lead of your DMM to that.  Then you can probe at the rear lights, 
to see how well they are actually grounded.  0.2 volt is probably 
acceptable, anything more than that represents a problem that could be 
fixed.


Thanks,
Roger


On 11/2/19 4:07 PM, Randall wrote:
>
> There may not be a good solution, Roger. The incandescent turn signals 
> draw a fair amount of current, which is likely more than the stock 
> alternator can deliver (along with tail lights and so on) at idle.  So 
> it may be that the battery voltage is dropping from 13+ volts 
> (alternator supplying all power to car) to  12.6 volts (battery 
> supplying some of the power) and the LEDs you’re using are sensitive 
> enough to show the difference in voltage.
>
> To check, connect a good voltmeter or DMM to the battery, then watch 
> what it does when the tail lights and flashers are both on.  If I’m 
> right, you’ll see the battery voltage sag in time with the turn 
> signals.  The only fix would be to convert to a more modern 
> alternator, that can keep up with the lights at idle.  (I’m not 
> certain, but I think there is a Lester unit that would look and fit 
> the same as the stock Lucas but give more current across the board. 
> Check with the Jaguar folks.)
>
> Another fix might be LEDs that use an active current source (so are 
> much less sensitive to supply voltage), but I have no idea where to 
> buy such things.  I made my own using a simple 2-transistor active 
> current limiter.
>
> To check for grounding issues, I suggest running a wire to the 
> negative battery terminal or negative starter cable, so you can 
> connect the ground lead of your DMM to that.  Then you can probe at 
> the rear lights, to see how well they are actually grounded.  0.2 volt 
> is probably acceptable, anything more than that represents a problem 
> that could be fixed.
>
> I’m not sure how the TR250 tail lights are wired.  On my TR3, all the 
> rear lamps ground only through their mounting screws, which go into 
> clip nuts fastened to the sheet metal.  Very insecure, especially if 
> the sheet metal has a fresh coat of paint.
>
> However, each lamp has a terminal inside the housing for a ground 
> wire.  So, I made up a ground wire that daisy-chains across all the 
> rear lamp holders, then leads around the trunk to one of the fuel tank 
> mounting bolts.
>
> -- Randall
>
> *From: *Roger Elliott <mailto:elliottr at rmi.net>
> *Sent: *Friday, November 1, 2019 12:50 PM
> *To: *triumphs at autox.team.net <mailto:triumphs at autox.team.net>
> *Subject: *[TR] TR250 LED tail light problem
>
> Here's the problem.  When the tail lights are on and I use the flasher,
>
> the tail/brake lights flicker with the flasher.  They don't go on and
>
> off but the get brighter and dimmer.  When the third brake light is
>
> hooked up it does the same thing.
>
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