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TR2/3/3A TR3 Turn signal note


Jedi Hopeful
My son and I installed the steering wheel, stator tube, and control head today and after getting it in we hooked up the wiring, reconnected the battery, and tested the horns (worked fine), and the left and right turn signals (oops). We were using an LED style shop test light and it lit properly when I activated the left or right turn signal on the control panel but it didn't blink as we expected. Hmmmm.... we then buzzed out all the connections to the turn signal flasher unit - all hooked up properly. It just refused to blink. I then tested out the wiring to my turn signal indicator on the dash as well as the bulb - both fine (this is a brand new Moss wiring harness we are using).

Oh well - we guessed we had a bad flasher unit. Beats having to buy a radiator...but wait!

After thinking a minute about that LED test light, I suspected that the flasher unit might need to see some resistance in the circuit, so I hauled out one of the actual front turn signal assemblies and we jury rigged it up instead of using the test light - viola! It blinks! Seems that the flasher unit needs to "see" the resistance provided by the bulb filament in order to actually blink. At least that's my theory. It blinked rather faster than I expected but I just bet that when we get both front and rear lights installed that it will function correctly.

In any case, just wanted to post this in case someone else might be doing a full resto and tried testing their turn signals without actually having them installed on the car.


Jedi Knight
You're 100% correct on that one, Landrum Family! And it's not just TR3s. All old-school flasher units require the load of resistive bulbs to function properly. In fact, if one of the bulbs goes out, it makes the flasher blink faster, alerting you to the problem.

All the guys selling fancy high-tech LED bulbs for your car also have to sell you the fancy high-tech flasher units to make 'em work as turn signals.


Great Pumpkin - R.I.P
That's right. The stock turn signal flasher on a TR3 (as on most cars) is deliberately "load sensitive". It must see a fairly specific amount of current, otherwise it will flash too fast, too slow or not at all. The idea being that it will thus warn the driver something is wrong if one of the bulbs is burned out.

Of course, it has also driven legions of Lucas electrics owners slightly batty, trying to figure out why they work sometimes and not others. If the overall circuit resistance is just a bit high (for example a corroded wire somewhere), the system may well work at speed but not at idle (for example).

One other thing to be aware of; some of the flashers sold as replacements do not in fact work correctly in the TR's turn circuit. They apparently expect the indicator lamp to be connected to 12v rather than ground.


Great Pumpkin - R.I.P
Moseso said:
All the guys selling fancy high-tech LED bulbs for your car also have to sell you the fancy high-tech flasher units to make 'em work as turn signals.
Or in some cases, an additional resistor to make the stock flasher work.

BTW, flashers sold as "heavy duty" typically are not load sensitive. Useful when towing trailers (for example).


Jedi Hopeful
It was a pretty satisfying moment. I suggested that we hook up the actual light instead of the LED-based test light and my son sort of gave me a look. When it started blinking, his expression made it all worthwhile.

A bit of payback for his being right about the need for that #$^%^ steering stator tube that doesn't appear on any TR3 maintenance diagrams :smile:


Jedi Hopeful
Don, we completely disassembled the control head - itty-bitty springs cams, and everything - in the process of fixing a non-functional and sticking horn button, so we learned exactly how the click-off mechanism works. While I'm sure most of you guys already know exactly how all this works, its was new to me. I'll try and create a document with graphics explaining it.
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