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MG TD TF 1500 - Blinking Instument Lights

I just converted all of my positive earth stop lights to LED's. One of the strange anomalies is that if I have my lights on at night and I signal a turn, my instrument lights blink.
Do you think I might need to rewire my dashboard?

Mort 50 TD

Yeah Mort. Make it look like this :-) Cheers
Peter TD 5801

P Hehir

That looks soooo good, you should have a plexiglass dash so your fine work can show through !
Steve Wincze

Thanks Steve. I guess it's my training as an instrument fitter that refuses to let go. Fiddling around upside down under the dash with wiring all over the place isn't my idea of a good time. I also fitted a 20 pin plug into the harness. The idea being if ever I do have to do any major work behind the dash I'll just remove it completely. Eight machine screws with butterfly nuts, a few cables to choke, speedo, tacho & starter & I'm sorted. The quick disconnect plug is just out of view in the foreground of the pic attached. Cheers
Peter TD 5801

P Hehir

Peter. Though your neat wiring job looks quite tidy I've got to say I'm a bit disappointed in you. That's not the way Abingdon did it. And I throughly you were the "Chief of the Originality Police". JK

Cheers Mate

Bill Chasser

W. A. Chasser

Settle down Bill. :-)

Improve anything that you can't see has always been my motto. I've managed some serious mods to the door locks & strikers by getting rid of all of the wood screws & you'd never know I'd done it. This is just one of many such 'invisible' improvements, including the 4.3, adjustable locks & strikers, removing doors without removing the trim, original thermostat housing refurb, 24433 water pump rebuild, cam, higher compression, better fitting valve springs etc. Apologies Mort for bending your thread. Could your issue be related to a poor ground? Cheers
Peter TD 5801
P Hehir

A mixed circuit of incandescent and LED globes can cause all sorts of issues.

Attempt to run LED trailer globes on a modern vehicle that has incandescent globe failure sensing circuitry and you will observe all types of strange phenomena.

I have managed to achieve a positive result using a mix of technology on my TF however I have been scrupulous in my connection methods.

Peter like your work however I found a propriety wiring loom from an Aus manufacturer provided a satisfactory and tidy outcome.
G Evans

Peter Hehir, where were you an Instrument Fitter, I am ex-RAAF.

P G Gilvarry

Very nice work indeed.
I am going to improve my wiring. It will never quite match your work for two reasons. The first reason is my skill level does not match yours and the second reason is that I have it added quite a few electrical modifications.

Turn signals.
Toggle switch for two modes of electronic ignition.
Power port for my GPS.
Oxygen sensor.
Toggle switch for airhorns and standard horn.
The Dual USB plug.
Battery cut off switch.
Toggle switch for auxiliary fuel pump.
Relays for lights, high beams and airhorns.
Heater fan three position switch.
16 position fuse block.
Warning lights for door locks.

All of the above does tend to complicate the wiring. I like your idea of the 20 pin disconnect. I may need more than one.

Do you have any more photos associated with this work that you can share eating here or direct to my email.
mortres at pobox dot com.

Any information you have on your 20 pin disconnect would also be appreciated.
Mort 50 TD

Peter I was at Williamtown NSW about 100 miles north of Sydney from 69 to 73 at 481 Maintainance Squadron working on general instruments, oxy & finally Mirage Air Data Computers. Before that I was in the Matra section on the missile guidance system. Now that was a great posting. Totally secure hangar requiring a Secret security classification to work there & coded pin access. The shuttlecock court was great & could be taken down in seconds whenever the access horn blasted as this usually meant an officer on the other side of the door. Also saw the moon landing there on an oscilloscope.

Mort the tidying up of the loom just requires some cable ties, a pair of side cutters & a little bit of thought. This is easily within your skill set. If you don't like the position of a tie just cut it off & add another. I'll send you some more pics & info on the plug. Maybe you could split the wiring into 2 looms, the first being the original stuff & the second your list above. Cheers
Peter TD 5801
P Hehir

There is a sub harness for the instruments. I gave one for shipping a few months ago.
Generally with a bit a Lacing like Peter used it looks very nice.
Rather than a multi pin connector I used bullet connectors and joiners as was original. I can remove the pre-wired instrument panel in a few minutes with little problem and the connections tuck under the dash nicely.

Jim B.

JA Benjamin


I must have gone very close to an encounter with you during my RAAF term. I was filling in time at Billsville, 76 Suadron waiting for a high security clearance to access my posting to the MK1 Bloodhound Squadron, was there for less than 12 months to have the boffins declare the missiles were obsolete. Small world sometimes.

G Evans


M Resnicoff

A few years ago I picked up some cheap LED 1157 replacements for my MGB. I found no real difference in illumination (ya get what ya pay for) but I ran them for quite a while. The B is a little different in that it has a seperate bulb for the rear turn signal while the running/park and brake share a dual filament bulb.
Stay with me I'm getting to the point.

When I installed the supercharger in the car about a year and a half ago I swapped out the electric temp gauge for a combo oil/temp gauge. Since it has two openings in the face for the needles the other gauges do not have you can see a small amount of light through the opening when the parking lights are on that you cannot on the stock gauges. After wiring in an A/F meter with a digital gauge and the new gauge oil/temp gauge along with a Vac/boost gauge I noticed that when I stepped on the brake that the dash lighting would illuminate. Odd! I spent the better part of the day checking all of the new wiring looking for the cause. I eventually discovered that there was nothing wrong with the wiring. The problem was with the LED replacements. They would back feed voltage from the brake circuit when energized to the parking light circuit of which the dash lights are part of. My suspician is that is by design of the unit in order you use all of the LED's when a brighter light is called for. What the units should have incorporated into the circuit was a diode to prevent the flow of voltage back though the park light circuit. I imagine there was one in there to prevent all of the LED's from illuminating when just the parking lights were energized.

I put the old filament bulbs back in and gave away the LED's. There are a number of vendors that have purpose made units for our cars that do give superior illumination...Lew Palmer for one who stops by here on occasion. They are pricey compared to the cheap crap I picked up but they are worth the cost...even though I haven't purchased any yet. If you have one units I suggest you send them a note. If you you picked up the el cheapo units good luck figuring out their circuitry. Just my thoughts.
L E D LaVerne

Thank you LaVerne,
I am only engaged in this project because of your initials.
I'll keep you posted.
M Resnicoff

L E D LaVerne

I upgraded the brake / rear lights and also the front side lights with leds. The indicators I left as tungsten filament because at 21W they are bright enough, and as they are only switched on for a short period, the power demand on the battery is minimal. The brake / rear light is a single bulb with dual function. I tried about three pairs of leds before I got the ideal solution. They do need to be tested as pairs I found - its no good just swopping the bulb on one side of the car and testing it. The other issue was finding bulbs that fitted the limited space. Anyway, what I have now work perfectly - bright rear lights that get much brighter still when I apply the brakes. I also fitted a high level brake light in tandem, which I attached to the top of the rear carrier. All this puts much less current through the hydraulic brake switch than the original bulbs did.
The front side lights were easy to find. I have the SVC style modification with two bulbs in the torpedo housing - one 21W bulb for indicators and one led for side. The led replaces a 5W capless bulb and is much brighter and uses 1W or less, but gives a much whiter light than any tungsten bulb. The 21W amber tungsten bulb only just overpowers it when flashing. I'll post images of either bulb if anyone is interested.
I had no issues with dash lights flashing or anything similar. I am using Negative earth.
Dave H
Dave Hill

Thanks, LaVerne. However, I only do the LED inserts for the ST51 (D Lamp), the Lucas 288 for S, V, W, and some Jaguars and Triumph Roadsters, the ST38 (Pork Pie)for the pre-war cars, and recently, the L647 for Mark II MGA and Mini Mark I.

For many others check out

Peter, I spent most of my career at Edinburgh, first as a RADTECHA and then became a Flight Engineer. Early on I did a one year stint at 3AD, before moving to the P-3 world.
P G Gilvarry


Rereading your post about backfeeding through the LEDs, I realize there is another (more likely) path. If the LEDs are on the same circuit as other incandescent bulbs, it is vital that the incandescents are wired EXACTLY the same. That is, all the bulbs need to have their bases on the same side of the battery polarity (normally ground) and the center tip of the bulb wired to the other battery polarity (normally hot). If even one bulb is reversed, it can lead to some very peculiar behavior of the LEDs. This is because the hot lead at the LEDs can backfeed through the incandescents. It seems strange, but try it sometime. Reverse the wiring, say on one of the turn signal bulbs with LED tail lights and you will often see some very bizarre behavior.

I have finished stripping all the wiring from behind dash and replacing it with some homemade harnesses. I used a total of three 12 pin connectors. By disconnecting two of them I can remove the dashboard without disturbing any wiring.
I have checked all electrical devices that I can check without the engine in the car and everything is functioning perfectly.
The LED lights and turn signals are amazingly bright.
The following are some photos of the completed project.
Take a look at the first picture I posted above and compare it to this one.

M Resnicoff

These are the connectors.

M Resnicoff

My wiring position.

M Resnicoff

Mate That is the best approach I have seen to date working on the under dash area of a T series, wish I had the same facilities and ingenuity to do this task prior to floorboards and seats being fitted.
G Evans

What is the fascination with various led bulbs in old cars? If your generator cannot keep up maybe its time to work on it or find someone who knows how to work on it to bring it back up to specification. If you are using some high current gizmo in your car you already have converted to a alternator, which means you have zero need for energy saving leds. If things are so dim at night, maybe you need to go see a eye doctor before you go completely blind. I do understand a lot of people who frequent this and other websites like it are simply trying to sell everybody on their worthless led conversion nonsense. So what is the point?
G Gilly

G Gilly,
Visual safety.
M Resnicoff

Hi Mort,
Don't know if this is related or not, but I put LEDs in my pinball machine. There is an effect called ghosting (I found out because they sell special non ghosting bulbs too) When the blinking light that is supposed to be bright is on, there is also sometimes another unrelated LED or two that will blink very dimly. Keith Murphy

I got tired of needing a flashlight to read my instruments,lol, so I put LEDs in the dash, pos grnd. Wow, for the first time I can read the instruments without squinting. The rest of the car has it's regular bulbs in place. The fog lights are on a relay though coming off the original harness. PJ
Paul Jennings

I rewired my TD last month and for the first time have working turn signals... but the incandescent flashing bulb was impossible to see. An LED fixed that. I'm getting one for the A next.

This thread was discussed between 11/12/2016 and 16/03/2017

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