headlight electrical problem

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headlight electrical problem

Postby Benedict90 » Fri 23.07.2021, 17:39

Hi folks,
my right headlight doesn't come up anymore, it's not the motor (I just restored it in autumn) and it's not the fuse above the steering wheel. I have no voltage at all on the cable when I turn on the headlights, the left side works fine. Do you have any tips where the cable is most likely to break or what else it could be?
I hope you can help me.
Greetings,
Bene
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Re: headlight electrical problem

Postby Rambo » Fri 23.07.2021, 19:43

Have you downloaded the relevant electrical diagrams ?
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Re: headlight electrical problem

Postby Simon_P » Fri 23.07.2021, 23:47

Do the lights light up or are they dead as well?
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Re: headlight electrical problem

Postby Benedict90 » Sat 24.07.2021, 06:57

Thank you for your answers.
Yes, I got the electrical diagrams.
And yes, the lights light up.
A month ago I had the same problem and after a short drive it worked again.
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Re: headlight electrical problem

Postby Simon_P » Sat 24.07.2021, 11:45

Check and clean the connections on the headlight module and continuity from there to the lift motor.
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Re: headlight electrical problem

Postby Benedict90 » Sat 24.07.2021, 18:09

Thanks, I've already checked the plug, it wasn't that.
I was just about to continue looking for the error, but it works again.
I think that's it when people say a car has character :P
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Re: headlight electrical problem

Postby KenCarson » Sat 24.07.2021, 18:54

I wonder if use it or lose it applies. Switches and relays need to be exercised regularly. Glad it's working so if it ain't broke don't try to fix it :-)
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Re: headlight electrical problem

Postby donsladek » Sat 24.07.2021, 20:28

Simon_P wrote:Check and clean the connections on the headlight module and continuity from there to the lift motor.


Also check your grounds - try jumpering from a known good ground to the motor ground.
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Re: headlight electrical problem

Postby Tuga2112 » Sat 24.07.2021, 21:07

headlamps control modules are one of those units that seem to be failing more often in the most recent years. and your description soudns like your going to have a transistor burned in the unit.


the topic has already been covered a few times. I Believe i am one fo the very few who replaced electronic components in the board to fix it but brit car nut may be able to sell you a brand new module.

anyway just for reference and help with your research take a look at this post
viewtopic.php?f=35&t=26938&p=348559&hilit=mosfet#p348559

this is where someone was having similar issues and i have added my 2 cents of experience when i fixed mine by removing the old transistor and replacing with a newer one of better ratings all around.

some people in the forum frown on my work because the new trnasistor is not attached to the board for heat sinking purposes. that is correct. but given the energy dissipated by the transistor i used compared to the original technilogy from 30 years ago, i found it to be overkill to heatsink the component when it was producing a lot less heat than the original one did (i think it was 8% but i would have to recheck all datasheets to confirm that)
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Re: headlight electrical problem

Postby Simon_P » Mon 26.07.2021, 19:35

Tuga2112 wrote:some people in the forum frown on my work because the new trnasistor is not attached to the board for heat sinking purposes.
Yes, never mind it can only fail, fall off or catch fire. Colin Chapman said if it works it isn't a bodge.

Tuga2112 wrote:i found it to be overkill to heatsink the component when it was producing a lot less heat than the original one did
would the power required, and hence the heat generated not be the same?
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Re: headlight electrical problem

Postby GeoffSmith » Mon 26.07.2021, 23:06

Simon_P wrote:
Tuga2112 wrote:some people in the forum frown on my work because the new trnasistor is not attached to the board for heat sinking purposes.
Yes, never mind it can only fail, fall off or catch fire. Colin Chapman said if it works it isn't a bodge.

Agree about heatsinking but I'd still bolt it down as vibration will eventually shake the solder joints apart or crack the pcb tracks.

Simon_P wrote:
Tuga2112 wrote:i found it to be overkill to heatsink the component when it was producing a lot less heat than the original one did
would the power required, and hence the heat generated not be the same?

On resistance (Rds(on)) is a lot less than the original. Drain current is the same (to a first approximation) so the power dissipated in the MOSFET is a lot less and the package can take it so it doesn't now need any heatsinking.
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Re: headlight electrical problem

Postby Simon_P » Tue 27.07.2021, 01:22

Makes sense. I saw that the original component got too hot and thought that it was working with the stall current.

So rather than implying a thermal incident by saying "...or catch fire" I should have said: Yes, never mind it can only fail, fall off or cause an electrical fire.
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Re: headlight electrical problem

Postby Tuga2112 » Wed 28.07.2021, 11:55

GeoffSmith wrote:
Simon_P wrote:
Tuga2112 wrote:some people in the forum frown on my work because the new trnasistor is not attached to the board for heat sinking purposes.
Yes, never mind it can only fail, fall off or catch fire. Colin Chapman said if it works it isn't a bodge.

Agree about heatsinking but I'd still bolt it down as vibration will eventually shake the solder joints apart or crack the pcb tracks.


I did not consider Vibrations as another reason to glue the new mosfet to the board.
Whenever it fails again (and i guess how long till that happens will be judge of how much of a problem vibrations really are in such lighweight items) i will reattach a new one by gluing into the board
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Re: headlight electrical problem

Postby Tuga2112 » Wed 28.07.2021, 12:07

Simon_P wrote:Makes sense. I saw that the original component got too hot and thought that it was working with the stall current.


that is one of the main reasons the original ones fail.

Simon_P wrote:So rather than implying a thermal incident by saying "...or catch fire" I should have said: Yes, never mind it can only fail, fall off or cause an electrical fire.

There's no exposed wires in the board,
I'm pretty sure the possibility of an electrical fire is reduced compared to the original unit due to the reduced internal resistance in the mosfet.

Im not saying what i did 2-3 years ago was the perfect fix, If i was to do it again I would do it differently, but I only dabble into things to the extent im confurtable with, and im happy to revisit work if it proves to be dangerous or fails again.
So far, that module is still going strong. im just expecting sometime soon the opposite side original MOSFET to fail, when that occurs, i can correct the instalation of both.
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Re: headlight electrical problem

Postby GeoffSmith » Wed 28.07.2021, 13:57

For a bit of background, take a look at this.
https://www.youtube.com/watch?v=I4Jcf3YbaoA
I've witnessed some interesting system level trials on ~1 tonne equipment - the vibration tables were monsters and subsystem resonances were eye-boggling.
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