Wiring issues with indicators and rear lights

[peterc]

Hi guys.
I have a query over my cars wiring due to some weird results when testing the new LED rear lights.
To save time climbing in and out of the car I chose to disconnect the two wires from the brake light pressure switch and add a link wire across their ends thus giving the system the impression that I was pushing the brake peddle. I'm sure that I have done this before when checking the brake light circuit/ pressure switch.

During the testing of the new LED's I had a conflict on the brake and rear light circuits.
E.g. Rear lights would not work whilst this link wire was in position on the brake light circuit !
Rear lights worked OK if brake circuit loop wire removed.
Brake lights worked OK without the rear lights on.
Indicator lights worked OK except that there was a slight pulsing of the brake light intensity.
I have checked the wiring back to the fuse box and seen no evidence of shorting out.
I decided as the final test of the day to just re connect the brake light switch and then try everything fully connected.
Yes, it all works but the intensity of the brake lights definitely indicates an small amount of interference when the flasher is working.
So any suggestions where to look for this interference.
Peter C

[nikbj68]

Hi Peter. Have you done these checks with the engine running? Might be less obvious with 13+V than purely battery voltage. There was always likely to be a small drop in the constant lamp when another flashes using filament bulbs, what is the equivalent wattage of these LEDs?
You could try a heavier gauge earth wire, direct to the chassis as near to the lamp as possible, pity it`s not possible to run a separate earth for each light.

[peterc]

Nik,
It is a thought but the LED's are meant to draw far less power than the old filament bulbs aren't they?
Trying more earths at the moment but will try with engine running.
Peter C

[nikbj68]

My version used x25off .33w LEDs, which is over 8watts total, (they were damned bright, but the beam angle was too narrow, rendering them virtually invisible from 20 degrees off-straight!) so if Paul`s are similar or more, then you might expect a drop in the constant light.
There is no lighting of the brake LEDs when the Indicator flashes is there? (without brakes on...)

[peterc]

Hi Nik.
Looking through the lens I would say absolutely no indication of any lighting up of brake LED's when their circuit is off and the indicators are flashing.
I've checked both sides.
So do we think I'm just being over sensitive to the fluctuation caused by the mass of LED's.
By the way it didn't make much if any difference with the engine running as far as I could see.
Peter C

[nikbj68]

OK, one last test. Cover the indicator as well as you can, and see how much the brakelight dips when you can`t actually see the indicator flashing. There may be an amount of 'optical illusion' adding to perceived drop in brakelight. If you`re still not happy with the brightness of the brakelight then, I`d suggest removal & benchtest, to confirm if it is a vehicle-based, or LED assembly-based issue, then follow the appropriate path from there... Good luck.

[goldie]

The lights have Voltage regulators that need a good 12V to work properly.
They should be steady when the engine is running or the Battery is well charged.
A non-fully charged Battery can cause this when the Voltage at the lights gets below 12V

[peterc]

I have just heard from Chris the designer of the LED lights who also suggested a battery was not 100% but it has been constantly on a battery monitoring system. Voltage just checked at 12.79V so pretty good and this was after starting to engine earlier and not having yet reconnected the monitoring system.

Nik, I was checking the brake light with the indicator covered by my hand to avoid the optical illusion. I had thought that there might be an element of light contamination across the length of the lense so I checked the opposite brake light to avoid that possibility.

Next job to check voltage drop between front and back of the car which should indicate if there is any dodgy connections.
So still hunting.
Peter C

[peterc]

The voltage shouldn't be lying and indicates a fluctuating voltage on the brake light circuit when the indicators work.
11.2 to 11.8V but a constant 11.8V when indicators switched off so I am not imagining the pulsing.
At least Chris confirms that I won't be damaging the new light boards whilst I continue to investigate. I always have visions of busting diodes or something with reverse feed.
Difficult to get a reading on the indicators whilst they are flashing as the meter can't react quick enough but suggest that there is definitely a problem on that circuit as it couldn't get over 10v.
Heh Ho under the bonnet and dash tomorrow I think.
Peter C

[spiyda]

Peter,

those voltages are way lower than they should be.
I would start by checking earth connection continuity all the way back to the battery negative terminal.
you can measure the actual return path resistance by using a wire as the return connection to the battery terminal,
then measure the wire resistance with your meter and subtract it from the first reading.

You should be able to do the same with the power wiring, but I would disconnect the battery first.

Chris (-=Spiyda=-)