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Discussion Starter · #1 ·
So I just converted all of my lights to LED using kit from Classic Car LEDs Ltd - very impressed, especially with the H4 LED bulbs.

Indicators didn't work initially with the original relay and I had to get an LED relay from them.

Now all is well, but randomly the tell-tale on the speedo only flashes when the engine is running, and not when the ignition is on but engine off. If I switch back to incandescent bulbs, it works fine. Tried with a battery charger connected, still doesn't work - requires the alternator to be creating juice to work.

Not really a major problem as I don't need the dash indicator when not driving, but anyone have any idea why it behaves like this?
 

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Discussion Starter · #3 ·
I'm not sure it is - the issue is present all the time. Needs the engine running and alternator producing a reasonable output to light up - very strange.

Even more odd, is that if I ground the bulb somewhere other than the speedo, it flashes fine even without the engine running... Possibly something to do with the way the oli/gen/indicator bulbs on the speedo are grounded?
 

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I'm not sure it is - the issue is present all the time. Needs the engine running and alternator producing a reasonable output to light up - very strange.

Even more odd, is that if I ground the bulb somewhere other than the speedo, it flashes fine even without the engine running... Possibly something to do with the way the oli/gen/indicator bulbs on the speedo are grounded?
The 3 tell-tale lamps at the bottom of the speedo are unusual because they have a constant live 12 Volt feed, (when ignition is turned on), and are operated by switched earth contacts.
Your test confirms that to make the indicator tell-tale work with the LED driver, it needs to be isolated from the live feed to other 2 lamps, and run the indicator tell-tale with a separate permanent earth and feed it with 12V from the LED driver.
A plastic bulb holder like the one on the Left, instead of the stock metal one, (on the right), would do that nicely.
Automotive lighting Gas Auto part Metal Titanium
 

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Discussion Starter · #6 ·
OK - so it was a bit more complicated than that! Managed to find a bulb holder (used in old 911s and 356s), and realised that simply grounding the flasher relay output just causes the relay to be on all the time with the dash light flashing.

Next idea was to put it on the other side of the indicator switch - i.e. use the 12v flasher feed from the indicator loom. This works fine, but to have it working for both directions requires diodes in the circuit - otherwise you end up with hazard warning lights!

This gave me a good idea. I had a random dash switch not connected to anything (put in by a previous owner), so connected that up to bypass the diode on one side. Open the switch, turn the indicator to that side and hey presto - hazard lights!

Final wiring diagram (ish):

Handwriting Slope Font Rectangle Parallel
 
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