Tuesday, 18 July 2017

Classic Mini LED indicator (turn signal) lamp replacement.

Still working on the Mini. It's coming along nicely, albeit slowly...

I did have a plan to reassemble things in a nice orderly manner. That's long gone out of the window! The best plan seems to be this:

1) Remove a part from the box.
2) Identify part
3) See if we can if the part, and if so
4) Clean/ paint the part and fit it.

With this in mind, it's recently come down to electrics.

Now the front indicator (turn signals if you're across the pond) / side lamps housings were made by lucas 39 years ago, from a sort of Mazak "monkey metal". Now this alloy doesn't age well, and mine were starting to crack up. Sadly there are long since obsolete, and good original ones now command a high price. Lenses are still available, however.

There are a couple of reproductions available. Some are quite expensive. Most seem to be made from ABS plastic of some description. Ideal. I chose these from Spyda designs, simply on price! (£31ea at the time of writing). Link Here . (Image stolen without permission from Spyda designs, sorry)

They rapidly turned up, nicely packaged.

They are quite a lightweight flexible construction, but this is no problem in use. They fit really well.

Nicely constructed, the PCB features three 1W yellow LEDs for the indicator section, and one 1W warm white, wide angle LED for the sidelight. The observant amongst you will notice there's a TO220 device in the top right hand corner, I suspect it's an LM317 or similar configured as a constant current source for the LEDs. Far better than a dropper resistor, and should ensure our LEDs have a good, long life. Great stuff!

The problem with fitting LED lamps is the dear old Lucas flasher unit buried under the dash. It's a thermal bi-metallic strip kind of thing, and relies on the current drawn by the lamps to operate. A normal flasher bulb is 21W ... these indicators are 3W .... the Lucas flasher unit just doesn't flash... it just stays lit up. This problem is exacerbated by the fact I've installed LED lamps in the rear too...

Because Mini didn't really change much with the times, there's another flasher unit by the windscreen wiper motor too! It's job is purely for the hazard warning lights (Four-ways if you're in the states!) This doesn't work either.

Now we could just shove in some 21W 6.8 Ohm resistors in the circuit in parallel with every indicator lamp (we would probably get away with 10W, as the duty cycle is about 50%), but that's a horrible bodge really.

OK, I thought about a simple 555 timer or discrete astable multivibrator driving a relay, until I looked on eBay. LED compatible flasher relays are no money ....
OK. So I ordered a couple to replace my two relays.... one turned up. Typical. (I've contacted the seller, the other is on it's way!!)

Now our dear old Lucas unit has two pins (actually some have three, but only two are connected), and doesn't give one iota about which way it's connected. This new unit has three pins, and I suspect it transistorised somewhere along the line, and is therefore going to get upset if we wire it up backwards.

The three connections are as follows....
L - Lamp - goes to the indicator lamps.
E - Earth - goes to chassis ground.
B - Battery - goes to the battery.

Only, of course it's not quite that straight forward. If we wired it up like that, our indicators would be permanently flashing, day in, day out....

So .... a quick consultation with the Haynes manual, and a poke round with the multimeter are required....

I will point out at this juncture that Mini had a long production run, from 1959 to 2000. Along the way some improvements were made to the electrics (and some of it wasn't!!). You may have a positive earth car if it's from the 50's or 60's ... you may or may not have hazard warning lights... and of course, Mini was exported all over the world, so local requirements would have changed the wiring...

Anyway... the original Lucas flasher was located hiding under the dash rail....

It's that round tin thing .....

... duly removed...

One side connects to a light green/ red wire. This is in accordance with the Haynes manual... good.

The other wire is blue with a red stripe. It *should* be a solid dark green. I can see further up the loom, that a repair has been made, and it does indeed join onto a green wire....

Now this is where things get a bit confusing. Having thought about this, I (mistakenly) thought this wire would simply supply 12V, via the indicator switch to the relevant lamp. Nope, there's a permanent 12 Volts there.... damn. This is why I have a hated for car electrics diagrams. None of the switches show a position. Scroll back up to the photo of the diagram, and have a look. 26 is the indicator direction switch. 25 is the flasher unit. 153 is the hazard warning light switch. 31 & 31 are the indicator lamps. There's obviously something missing. Some lucas magic going on in the hazard switch? There's no such thing as magic....

No, here's what happens. 12 volts gets to the original flasher unit. It's output goes to the lamps, via the indicator direction switch. Once the switch is made, current is drawn through the lucas flasher, which starts to warm a bi-metallic strip inside the unit. Once it's been on for a second or two, the bi-metallic strip opens the circuit, and starts to cool as no current is being drawn. Once it's cool, it closes the circuit again, and the process repeats.

Right, but what happens to my new flasher unit, if it's getting a supply (and earth) simultaneously? Is it going to sit there clicking away, annoying the hell out of me, even when my indicators aren't on?

As it turns out, no. It actually needs to see a load to operate, exactly like the old lucas unit. Just not much of a load!

So, the dark green wire goes to B, and a new earth wire goes to the chassis and pin E.

Works a treat....

The hazard warning flasher is wired up the same, and works flawlessly too..

Light green and brown goes to L, and the wire from the inline fuse holder, connects to B.

How, back to work.... ;)


  1. A fascinating restoration indeed, I have been following with great interest. How do the Lumens from the LEDs compare to the incandescent units?
    Good luck with the rest of the project and I'm sure that you are enjoying every minute!

    1. The output of the LEDs is damn close to the originals. Huge update coming soon... watch this space!