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MG TD TF 1500 - Installing LED Tail Lights in TF

Installing LED Stop & Brake Lights
A Saga of Unintended Consequences
by Don Harmer

After Geoff Kent's inspirational Tech Session in March on “LED’s, Owls and the Quest for Enlightenment” we decided to outfit my TF with LED taillights. Scott Sewell presented a somewhat easier LED solution for those of us that use 1157 or 1156 bulbs in the tail and side lights as in the TD and TF
superbrightleds.com offers non-polarized dual intensity high power LEDs in white, yellow and red in the 1157 bulb. If just replacing the tail lamps, the original flasher may be used. If the side lamps are replaced also then a suitable flasher must be added if you have turn signals.

The installation was easy as it just required removing the old incandescent 1157 bulbs and inserting the new superbright non-polarized 1157 based led bulbs. A test showed the tail-lights, stop lights and the turn signals all worked without installing a LED compatible flasher.

Pleased with the ease of conversion, we also installed positive ground, screw based dash lamps from Moss. You could finally see the instruments at night. After all our conversions we closed up the garage.
Fast forward a few days. I went to get the TF out for a run and had trouble starting it. Even with using starting fluid it would run only a few seconds and shut down. Drove my Detroit iron instead.
Thus began a search for the problem, was it a gummy alcohol based gas causing fuel line or filter plugging, or some other fuel problem?

Checked the power to the pump and cleaned connections. No help!! still would not start.

After removing the fuel line at the carb and seeing only a single click of the fuel pump when turned on, we decided that my 40 year old SU pump had finally given up the ghost and ordered a new solid state one from Moss.. When the new pump arrived Scott installed it and the new pump didn’t work either. DANG! Tested both pumps directly connected to the battery with jumpers !and both worked.

Was the tank filter or the line to the pump clogged? We were set to drain the tank, clean filters, blow out fuel lines. etc.

Then I remembered a similar problem on the MGB when the fuel pump ground at the license plate was bad, but the pump worked until a taillight burned out.
We tried a separate good ground to the pump and it chirped happily away.

Changing the taillight to non-polarized LEDs had created the problem somehow. WHY!!!!
To understand, one must look at the grounds. The fuel pump, tail lights, gas gauge and license plate lamps are all grounded by separate wires to the 5/16 bolt that secures the spare tire carrier to the frame, creating a stack of 5 eyelets and two washers. held on by a single nut. If dirt or corrosion keeps these from getting a good connection thru each other and to the frame then the pump is no longer well grounded. However a path thru the tail light filaments to the hot lead of other bulbs in parallel and thru them to ground can occur (so called leakage currents).
Note that the front marker light, dash lights, and perhaps the license lights filaments are all in parallel providing a low resistance path to ground.

Installing the “polarized” LED’s inserted diodes in the leakage path that prevented current flow thru the other bulbs to ground. So now the fuel pump no longer had a path to ground. and could not work.

Unintended consequences!

Electrical problems are almost always grounds!!
Don Harmer

Great write up Don on LED's and the checking of electrical faults. Useful information when the time comes for me to install LED's - especially for the rear tail lights.
Frank Cronin

Don, I looked at their site, can you tell me which bulb you used. I looked at several 1157's and they all showed as polarized.
MG LaVerne

LaVerne

I just checked, and my bulb, 1157 LED Bulb Dual High Power, part # 1157-R3W-G is listed as out of stock, (discontinued)

They also list #1157 X 18 T (140 Lumens) and 1157 X 1W G (70 lumens) as nonpolarized but not sure these are equivalent.

I have an inquiry in to support to see if we can get the original bulb.

Will keep you posted

DANG!
Don Harmer

Dang is right...I had my wallet out for set at the prices I saw.
MG LaVerne

I used positive ground LEDs from www.litezupp.com..
$27 each.

Simple swap out. Flasher also worked - enough resistence in the front signals on my TF.

Best upgrade ever ;-)

Dave
D Moore

An email to Superbright fpund that the bulbs I had specified above have been withdrawn for "Quality Control" problems. I was unable to find an equivalent brightness bulb in their non-polarized offerings.

Google search led me to Amazon, and JDM Astar 800 Lumens Superbright AX-2835 Chipsets 1157 LED Bulbs at $16,99 per pair in red. white and amber Also in 1156 versions. All these are non-polarized (work in positive or negative ground systems)

Not only are they brighter (800 vrs 170 lumens) but they are much cheaper ( $8.50 to $29.00 per bulb)

They also sell 6 ohm resisters to correct current draw for flashers if needed.
Don Harmer

Thanks Don.
MG LaVerne

STOP THE PRESSES

The JDM Astar 800 Lumen bulbs from Amazon ARE POLAR and can only be used in Negative Ground systems

The description of the "Xenon White" in the ad says they are non Polar but I just tried them in my TF and no light.

The red and amber have an identical description but omit any mention of polarity.
The "Brilliant Red" also does not work in positive ground cars ( I tested it also)

They both work OK in my B-GT neg ground

SO my above solution was false, based on the near identical product specifications, one of which falsely claimed non polar

I'll keep looking
Don Harmer

Don,
I confirm your last post above. I contacted JDM Astar via e-mail and they confirmed polarity on all their lamps. This was their reply:

"Dear Mort
Our 1157 led are polarity sensitive , can not work on positive ground system. Do you know how to rewire to negative ground ? almost 99% 1157 led bulb on the market are polarity senstivite. If we have non-polarized bulb in the future , we will let you know
Sincerely
IVey"


I have also been in contact with Jim Thompson from LiteZupp. This is one of his responses:

"Morton,
The LED's need to point in correct direction. If the glass lamp points up or down you will need the LED's mounted in one our right angle housings.

LR57RP -- Red Positive Ground
LR57AP -- Amber Positive Ground

If your glass lamps straight forward or backward you will need the following.

L57RP -- Red Positive Ground
L57AP -- Amber Positive Ground

Let me know if I can provide additional information.


--
Jim Thompson
LiteZupp Industries, LLC
VBTek, LLC
817-337-0562
jimt@ieee.org

80 TR7 73 Stag
Smithy Granite"

I will pursue this one and post the results.
Mort
Mort 50 TD (Mobius)

Doh! I ordered two sets of these bulbs, one for the TD, one for the TF. Maybe I can take them apart and reverse the polarity. If they were only one pole bulbs I could just swap out the wires. Grr. Oh well...
-David
D. Sander

This thread was discussed between 25/04/2014 and 09/05/2014

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