[OMFBullet]

I was keen to upgrade the indicator tell tale, I felt the poor visibility was a safety hazard and reading a few posts it seems other have had a few issues too. Checking things out it seems that inserting an LED bulb is simple, if a little fiddle removing the housing from the base of the speedo. Full left hand lock and easing with a screwdriver helped a lot. The LED worked fine - but only with one side flashing.

The tell tale is fed by two wires, the power feeds for either the left or right hand flashers. The bulb is earthed via the dead feed. However LEDs are polarity conscious and therefore will only work in one direction. I gather that AC, rather than DC, LEDs are made that would have solved the problem but I couldn't find any. Plan B is a diode kit, £9 from a well known auction site. In essence both feeds go into one wire via diodes, one way valves as it were, preventing power flowing back. These feed into one of the wires to the tell tale, the other tell tale wire runs to earth. If the bulb still doesn't work then turn it round to adjust the polarity. Mine also needed a little fiddle as well to ensure a good contact.

I fitted mine in less than 30 minutes. Taking the headlamp off made life easier in terms of accessing the tell tale wires. I cut these, fitted the bullet connectors and patched in the harness. The earth ran to the speedometer bracket. The bulb holder was inserted back in the speedo and for good measure i also replaced the neutral light. Job done in less than 30 minutes at a cost of around £12.50 for bulbs and wiring kit. 

I attach a few images to show the basics. Apologies if I am walking on well trodden ground here, but posted in the spirit that it may help somebody else. 

[Nitrowing]

Good stuff!
I fitted LED indicators too, along with an LED repeater - which only blinks when 'Left' is selected 
I didn't bother following up a fix but it's nice to see you've done it 

[Haggis]

Halfords led 501 work just fine.
Does not say on the pack that they are bi-directional,  but they are.
They flash correctly for left and right and is much brighter.
I also fitted them to the high beam and neutral positions.

https://www.halfords.com/motoring/bulbs/501-white-led-car-bulb-halfords-essentials-twin-pack-724090.html

[OMFBullet]

That’s interesting, wish I had known that. They must be AC bulbs as the feeds are left and right live. I searched high and low for bulbs of this type but with no luck. I bought a pack of ten LED bulbs but have avoided replacing the high beam until I have driven at night. I read on another forum that there is a possibility that it could be too bright, similarly with the dial illumination. I am now thinking about an LED stop/tail light.

[Nitrowing]

am now thinking about an LED stop/tail light.

I replaced the pilot lamps for LED. Very noticeable difference.
Tail lights are worth doing too, I haven't got a photo though 

[Ove]

+1 for Halfords. I was lucky, didn't cross my mind I might introduce the problem you found.

It is a safety issue, I've left my indicator on without realising (I think the cancelling motion needs a more deliberate push then previous bikes) and had someone pull out on me, thinking I was turning off.

[OMFBullet]

As with Nitrowing I too replaced the pilot light bulbs with LEDS, another pack of ten for about £4, and they are certainly much brighter. I did take a photo at the time of the before and after and the difference is very clear.

[AzCal Retred]

The bulbs aren't particularly AC adapted so much as just polarity protected. They have a diode bridge internally so they don't care about socket polarity. The flip side is that the hardware store is full of low wattage LED 12 VAC "Malibu lawn lighting" hardware that works fine on 12 VDC...

[Adrian II]

All-DC lighting on the UCE/EFI models, AzCal.

A.

[AzCal Retred]

Right you are Adrian, but the single turn signal indicator bulb needs to be bi-directional, as it grounds back thru the unused side lamps when the turn signal is selected. An incandescent doesn't care, but OMFBullet had constructed a very nice work-around to make his LED indicator lamp work. Unfortunately Haggis pointed out that there were already bidirectional/AC versions available that rendered all that nice, creative work moot. Still, a worthy effort. 

[AzCal Retred]

A secondary issue is that the bulbs serving as ground path have to pass enough current to reliably light the indicator bulb AND operate the flasher. LED's may or may not accomplish this. If you have an electronic flasher, there is likely no problem. Anyway, I ended up using two incandescent bulbs in the front trafficator lamps. I figured they were easier to keep track of. My new 80 MPH speedo won't have any of that indicator mess in it, so problem solved, I can go back to all LEDs. Hi/Lo can always be checked by looking at the switch, and I'm pretty sure I can figure out if I'm in neutral.   

[JohnnieK]

Hi/Lo can always be checked by looking at the switch, and I'm pretty sure I can figure out if I'm in neutral.   

My C5 is often in neutral without the neutral light showing.

[Nitrowing]

My C5 is often in neutral without the neutral light showing.

My ElectraX too 😅