Has anyone ever...diodes in the indicator circuit

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zeaphod

zeaphod

Well-Known Member
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Belfast, Norn Iron
Bear with...
After tinkering with LED indicator bulbs recently, it seems that because of the way the tell tale (dash) bulb is wired across left and right circuits, there is enough leakage across this bulb to partly light the opposite indicator side - when you switch left, the lefts come fully on, but the rights partly light too.
It looks like fitting a couple of diodes (to isolate the feeds) between the GR and GW feeds to the dash bulb, and earthing the other side will still allow the tell tale to work, but will also isolate both sides of the circuit.
Has any eejit tried this? Am I wasting my time? Do the "proper" indicator units have built in resistors?
 
Hmm. I'd be surprised if it did. If I was getting that I'd suspect earths, as with most Land Rover lighting faults where lights come on together. Have you got a flasher control unit/relay that's suitable for LEDs? Or just the normal one?
 
How would a couple of diodes help?
Why not rip out the dash indicator light (to stop the "wrong side" being dimly illuminated) and plug a 12v buzzer across the LGN and earth on the flasher unit.
This is an MOT pass thing too, audible flasher warning & if its loud enough you can even hear it above all the noise in the cab!
Or use 2no dash indicator bulbs, LHS & RHS, a bit more wiring needed perhaps.
 
Don't fully picture what you are suggesting in my minds eye but I don't think you can achieve what you want with two diodes. If you isolate one half of the warning bulb it wont light, if on the other hand you are suggesting using the diode to 'bypass' the opposite side indicators then aren't you only just adding another diode in parallel with the existing indicator diodes? As you are suggesting one end of the diode is connected to earth (you didn't mention if it was anode or cathode) I'm assuming you are paralleling the diode with the indicators, if it is the cathode you earth then as soon as you apply power to the indicator the diode will effectively short it to earth and either burn out or blow the fuse / relay. Can you post a rough drawing of what you are suggesting?
 
An other solution may be to add a load resistor in parallel to each set of indicators (something like 12 ohm, 20 watts) as that should provide sufficient load to stop the opposite side lighting as long as the relay can take that load 9assuming you are using an LED one)
 
Last edited:
zeaphod said:
Bear with...
After tinkering with LED indicator bulbs recently, it seems that because of the way the tell tale (dash) bulb is wired across left and right circuits, there is enough leakage across this bulb to partly light the opposite indicator side - when you switch left, the lefts come fully on, but the rights partly light too.
It looks like fitting a couple of diodes (to isolate the feeds) between the GR and GW feeds to the dash bulb, and earthing the other side will still allow the tell tale to work, but will also isolate both sides of the circuit.
Has any eejit tried this? Am I wasting my time? Do the "proper" indicator units have built in resistors?
Click to expand...

As an electrical engineer I can confirm this is not a mad idea but one that could solve your problem. As you have quite correctly discerned this would stop the leak back at the telltale light.

However, I suspect that to be honest this may be more of an earth issue, it is only now showing it's ugly head as LED's require such a small current. I'd clean up the earths and see what happens as the earth should be the easiest route 'home'!
 
Thanks all. At least I'm not mad to have thought of it. I don't think there's another earth source - the dash bulb uses a resistive earth through the non lit side from the indicator bulbs. The load resistor should work too, but this seemed neater.
 
9acd78b208e6f601ecb3c736eb7f380e.jpg

Hope this image attaches. It's back to front - of course, the camera on this thing is front facing only! Anyway, the bulb shown is the dash telltale. It normally has a feed from each side of the indicator wiring, gr and gw. These will be cut at the plug, and the feeds connected in series with a diode. The ends of the diodes will be connected to one side of the bulb and the other will be earthed. This isolates both sides of the indicator cct in normal operation. Current flow is restricted by the bulb.
 
Thanks!
As I've got the attention of a few folks who seem to know their way around, would a pair of 1N4001S work OK? My electronics training happened 30 years ago, I'm a bit rusty. Maplin is handy, are their own branded diodes OK?
 
Any of the 1N4000 series diodes will work, all are rated 1A, from memory the '1' has a PIV of 50v going up to 1000v for the '7'. Whatever you can get will be fine in this application.
 
diode conns.jpg

plug conns.jpg

earth connection.jpgJust to finish this off, I installed the diodes this afternoon, and it's all working OK. The attached snaps show the connections (poorly). The connections are all soldered and heat shrinked with the exception of the earth - taken from the hazard switch supply without cutting the wire. This is soldered and taped up. No leaking of power to the non switched side, and the LED indicators are much brighter than the older type. IIRC the diodes were about 50p from Maplins.
 
Zeaphod,
I want to do the same mod to my Defender but I can't quite understand what you did. Can you explain more clearly?
1. I understand that you took the GW wire and you grounded it. Confirm you did this by splitting the wire and then grounding the split off wire?
2. I understand you Split the GR wire, and placed diodes in the parallel wires, but then where did those go?
Boltonbits sells a mod for this which looks like they just run a ground wire to the back of the light harness for the turn indicator. Are you familiar with that mod?
Thanks.
G
 
g chand said:
Zeaphod,
I want to do the same mod to my Defender but I can't quite understand what you did. Can you explain more clearly?
1. I understand that you took the GW wire and you grounded it. Confirm you did this by splitting the wire and then grounding the split off wire?
2. I understand you Split the GR wire, and placed diodes in the parallel wires, but then where did those go?
Boltonbits sells a mod for this which looks like they just run a ground wire to the back of the light harness for the turn indicator. Are you familiar with that mod?
Thanks.
G
Click to expand...

The way I understand it is, there are 2 positive feeds to the rear of the bulb. One for each side, both green with a trace colour.

Cut both of these green wires leaving around an inch or 2 of tails on the bulb.

Then solder a diode to each of the wires connected to the harness (not the tails still connected to the bulb) note polarity on the diodes.

Once you have the diodes soldered, solder a black wire to one of the tails on the bulb, it shouldn’t matter which one you choose.

Earth the black wire.

Solder the two “spare” legs of the diode to the “spare” tail on the bulb.


Should have looked at your profile really. It’s common decency here to introduce yourself in the relevant section too.
 
Thanks Capo,

I already have a working updated Wipac relay. The RDX relay didn't change anything for me. I'm aware of the boltonbits mod but wanted to see if I could wire it myself.

And I guess I messed up on my online forum etiquette. My name is Garrett. I have a Defender 90. I'm not sure what else I need to share. Thanks for all of your expertise!
 
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