LED installation problem on my WO 4.5L

[Chris Card]

In order to improve the side and indicator lighting and, at the same time, cut down on electrical drain, I’ve installed LED bulbs all round. Some time ago I did the tail and brake lights with no problems. However, changing the indicators has given me a real headache. Any advice would be gratefully received and the problems are listed below.

1. The car is wired negative earth.
2. The front indicators are in the side lights and the LED “bulbs” are twin filament, giving white side lights and orange flashers. The LED tail flasher “bulbs” are single pole, and I’ve had to convert the previous twin pole bulb holders (live and earth) to single pole, creating a new earth to the chassis, having disconnected the original one.
3. The new LED “clicker can” has three pins, whereas the old “normal” one had four pins, so I have what seems to be a spare earth.
4. I have wired the LED can, as instructed, with power to 49, 49a to the indicator switch, and P to the tell-tale buzzer, and the indicators will work. However, if I switch on the electric fan, dash lights, wipers, fog lights or horn, none of which now work (they do if fed from a test circuit), the indicators stop working in sympathy.
5. I’ve checked that I have power to the auxiliary switches, but when I switch them on, the power “disappears” and the + (and -) terminals seem dead.
6. The fog lights and the horn are wired through separate relays.
7. The side, tail, brake and head lights all work as before.

Chris

[John Murch]

Chris, I can offer no help, but you have my most sincere sympathy with your problem! I assumed that these things only happened to me.
John

Ps
Draw a wiring diagram of the set up, somewhere two + or - must be meeting! And speak with the supplier of the flasher unit, is the spare terminal for a dash repeater light.?

[Charles R Simmers]

What model Bentley are you working on?
Can you draw a rough schematic of what you've done so far?
LEDs should be a straight-forward swap.
Also, the source and part number of the LED units you are using would be helpful.

Best,
Chuck

[Steve Welton]

I wonder if the car has one of those DB10 relays fitted?
This allows rear brake lights to act as indicators. Used on many cars in the 50's & 60's including MG's, Austin Healey's, AC's & TR's. There was one on my 3L which created difficulties when fitting LEDs.

[Robert Craven]

I've sometimes found (particularly on other cars) that weird faults where lights do strange things when a combination of lights is switched on are due to (sometimes obscure) earthing faults. A connection or joint can be good enough when low current from just one item flows through it, but higher current from more than one item causes the problem.
A meter will show the correct voltage, but a meter takes so little current the faulty connection doesn't become apparent.

[Chris Card]

Robert - my guess is that it is an earth problem, but how to identify it . . .?

Chris

[Robert Craven]

Chris,
Perhaps you can run a stout long lead from a good earthing point with a crocodile clip or similar on the other end and connect it in turn to the various lighting points which should be earthed and see whether it makes a difference at some particular location.

[Christopher Carnley]

Maybe you need to split the earth connections with the frame, and make more earths close to the individual fittings. Return polarities may be unbalanced.
Robert is right about the quality of the earth connections.

[Chris Card]

Many thanks for your input and, in response to Chuck's request for a circuit diagram, I've been constructing a .jpg file from the tatty photocopy that came with the car. It was professionally rewired in 1992.
The flasher circuit is on the diagram and it emanates from a live junction box that it shares with the wipers, dash lights, and fan, all of which are affected, so I guess there's a clue there somewhere.
I've not changed anything apart from swapping the flasher can for an LED friendly one, rearranging the earths to the rear flashers (single, instead of twin pole "bulbs"), and ending up with a spare lead from the original flasher can that had four instead of three terminals. The spare seems to be an earth, but . . . . ?
I'm still completely foxed and getting too b....y old to be lying on my back under the dashboard, with my feet hanging in the air over the backs of the front seats!

Chris

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[Charles R Simmers]

Let me study this. I'll get back to you tomorrow.

-Chuck

[Chris Card]

Chuck. - many thanks. I believe the schematic to be basically accurate but, subsequent to 1992, the body came off for restoration and retrim (also by James Pearce), later, an overdrive was added and other mods to the wiring may have been carried out by different people, so . . . .

Chris

[Charles R Simmers]

Chris,
All the affected circuits seem to tie to the positive junction box. I assume you have already checked the box for any shorts to ground and cleaned all the corrosion from the contacts in the box and the fuse block. Also, are fuses 4,5, and 6 intact?
What happens if you disconnect the 49 terminal of the flasher? Do the other circuits work then?
If they don't work, pull fuse 4 and feed +12V directly to the junction box. Any effect?

Let me know the results of the above tests and we'll get further into it.

Best,
Chuck

[Chris Card]

Hi Chuck - I've been a bit tied up with other "stuff", but what I have established is that everything running off the 10amp fuses works. Nothing works properly on the 35amp circuits.
I pulled the feed from 49 as you sggested, but that had no effect on the semi dead circuits
My multimeter indicates consistent voltage everywhere, it just dies when anything is switched on. I just ran a check on the wipers by connecting a feed direct from the battery and they worked fine - the same with the cooling fan. Running bypass earth leads has no effect.
I'm still completely foxed, but getting better at crawling under the dasboard without cracking my head on the pedals or dynamo!

Chris

[John Robins]

Hello Chris,

We've never met, but if your hairstyle is similar to mine, can I suggest wearing a balaclava!

[Charles R Simmers]

Hi Chris,
OK, so there is nothing obviously wrong with the indicator circuit.
It sounds to me like a high-resistance wire or connection between the battery, combo-switch, and the positive junction block. Your multimeter read +12VDC until a load is connected. then, it drops to zero. This can be caused by a corroded or dirty connection, a pinched or partially cut wire. or a loose connection. You are going to have to backtrack from a non-functioning load back to the battery.
You have already checked the loads themselves and they all work when feed a good, clean +12.
1. Hook the loads back up to the junction block.
2. Pull fuses 4,5, and 6 from the fuse box.
3. Feed the junction block with a direct wire from battery positive to the junction block.
4. Does the wiper and dash lamps work now?
5. if Yes, the problem is further up the line.
6. Apply 12V to the output of fuse 4 terminal.. Does the wiper and dash lamps work now?
7. If Yes, bad wire from fuse box to junction block.
8. If No, reinstall Fuse 4 and connect 12V to the input to fuse 4. Does the wiper and dash lamps work now?
9. If No, bad fuse.
10. if Yes, the problem is further up the line.
11. Apply 12V to the output on the combo switch. Does the wiper and dash lamps work now?
12. If yes, bad wire between combo switch and fuse box.
13, If No, I give up since all other circuits emanating from the combo switch are working.

Good luck,
Chuck.

P.S. Multimeter will show full voltage even if a very small current (< 1mV) is flowing. So they are not very good at diagnosing weak connections or wires.

[Chris Card]

John - I'm not sure about the style, but more hair would probably help!

Chris

[Chris Card]

Chuck, you are a genius! The problem is an arking negative terminal on fuse 4, which has corroded/welded the terminal. It must have been gradually happening over a long period as I can't unscrew the terminal. I will now have to source a new fuse board and reconnect - unfortunately it's in a very awkward position, high up on the inside of the fire wall. I think it will require one of the more athletic positions from the Karma Sutra! I'm investigating . . .
The LED installation seems to have been a coincidental red herring.
As a thank you for your time and advice, I've attached a virtual bottle of 12 year old single malt. Enjoy.

Chris

[Charles R Simmers]

You are very welcome and thanks for the 12 year old.
-Chuck

[Chris Card]

I've just finished wiring in the new junction box, replaced a short length of burnt wire and, hey presto, everything works - except my back! Chuck, I can't thank you enough for your input into this. I was barking up the completely wrong tree by searching for a dodgy earth, instead of a lack amps due to a faulty/burnt connection at the fuse box.
As it all happenned as I changed the indicators and side lights to LED, I assumed that the problem must be associated with that change. Your bit of lateral/logical thinking has saved me endless fruitless hours of looking in the wrong place.
Thanks again.
Cheers.

Chris

[Charles R Simmers]

Glad to help. It's something I do every day. I'm an Automotive Electronics Engineer for a large semiconductor company. Most of my day is taken up with diagnosing customer design, implementation, and production problems.

All the best,
Chuck