[TR] TR250 LED tail light problem

Wed Nov 13 05:31:20 MST 2019

I seem to remember seeing those also, somewhere, some years ago, etc., etc. I can’t tell from the description if the following bulb holders have the grounding tab or not.

https://www.spitbits.com/store/51-BULB-HOLDER-STOP-TAIL-LAMP-MK3-GT6-2req--P2247.aspx 

Alex Thomson

’73 TR6

’71 GT6

From: Triumphs [mailto:triumphs-bounces at autox.team.net] On Behalf Of Brian Kemp
Sent: Wednesday, November 13, 2019 12:15 AM
To: Roger Elliott; triumphs at autox.team.net
Subject: Re: [TR] TR250 LED tail light problem

I seem to remember once upon a time, somebody made a light socket with a ground wire or a ground tab.  I looked a few months ago for my GT6, but couldn't find it at the usual vendors.  I imagine you could add a ground wire, but some of my sockets are pretty bad, so I was looking for new ones that already had the wire.

On my TR6, I did have a socket that didn't conduct well to ground.  The problem was the connection between the metal base and the metal fingers.  I just hit the area with a wire brush in the Dremel then soldered the two bits together and it fixed that problem.

Brian

On 11/12/2019 2:38 PM, Roger Elliott wrote:

I decided to give up on the issue.  

There did not seem to be much of a voltage drop across the battery - about .05 volts as near as I could make out.  It's possible that either the meter or myself were not quick enough to read accurately.

As far as I could tell there is not a ground terminal on the sockets.  There was about .009 volts between the lamp housing and the battery.  I did run additional wires from the lamp housing to a ground (to the tank mounting bolts).

The brake/tail lights still varied with the turn signals, in opposition, got brighter when the turn signals were off.

Tested the lights with regular brake lights instead of LEDs. I noticed the brake/tail lights still varied with the turn signals.  This is when I decided to give up and just live with it.

Oh, the third brake light that I have wired in - power from the brake lights and grounded to the body flash when ever the brake lights and turn signals are on (like the brake/tail lights in opposition.

Thanks for your help.
Roger

On 11/3/2019 4:37 PM, Randall wrote:

Yes, that’s the idea.  You want all the lights on (including turn signals) during this test.

What you’re looking at is how much voltage drop there is through the ground path.

-- Randall

From: Roger Elliott <mailto:elliottr at rmi.net> 
Sent: Sunday, November 3, 2019 1:26 PM
To: triumphs at autox.team.net
Subject: Re: [TR] TR250 LED tail light problem

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
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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