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Looking for some suggestions as I am currently at a loss...

I realised the other day that my dipped headlights on my TR5 were not working. Sidelights work OK and the main beam works OK...

From the foot switch I measure 12v leaving the switch for the dipped headlights and this is confirmed at the bullet where the cable splits to the headlights. When I connect this bullet with the other two to the headlights the voltage shows zero.

Switching to main beam everything works fine and 12v is shown at that connection to the lights.

So, I disconnect and reconnect the dipped lights and suddenly it works - quite happily switching between dipped and main. Switching on and off etc. Return to the car 5 minutes later and the dipped lights don't work again...!!! The car hasn't been touched at all in the meantime. From the dipped lights working, they suddenly aren't - the foot-switch still shows 12v leaving towards dipped beam but they just don't work!

I'm getting really frustrated and pulling what's left of my hair out!

Any ideas what the problem could be?? Hopefully it's something ridiculously simple and will just serve to highlight my complete incompetence! :-)

Thanks,

/A

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Pretty likely this is just a bad joint somewhere and it's most likely to to be the bullet connector.  If the voltage is there off-load but not when the connection is re-established, there is some resistance in line which is 'dropping' the volts when current is taken (your meter probably draws such a low current that it shows full voltage despite that resistance).  I would start by thoroughly cleaning the bullet connector and its socket,  including the  other bullet from the light assembly, and making sure the bullets are making a good connection to the cables.  Also check they are tight  when pushed in the connector.  You may have temporarily 'fixed' it before by wiggling things. 

Multimeters are not the best things to use for fault-finding on vehicle wiring, because they take such a low current.  Much better to use a  small bulb with a couple of flying leads. 

Edited by RobH
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Thanks - I haven't moved to the bulb end of the cables yet, will do that next. I have changed all bullets and sockets already.. The strange thing is that it will sometimes work after reconnecting everything and then not - without touching/moving anything...

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If you have already replaced the intermediate connectors it probably points more to an intermittent fault with the switch. ( I take it the main beams still work OK which probably eliminates earthing and similar problems at the bulb end which are also quite common.)

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Main beams work without a problem and I keep testing at the switch but the voltage at least seems ok each time I switch between main and dipped.

What I am particularly not understanding is that if the main beams are on then I continue to measure 12v at the junction (to both lights). If dipped then I measure 12v to the 'live' bullet but as soon as I make the connection between this bullet and either one or both of the wires for dipped lights then I suddenly get 0v. This makes me feel that the problem is beyond the connection and not at the switch end...? I assume the earth is common to both main and dipped...

 

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If the voltage disappears when you put a load on the wire, the problem is at the source end, not at the load. If there was a short at the bulb end you would blow the fuse and you haven't said that happens. As I said, I think you are being fooled by your meter, which can show 12v even though the connection is bad.

Try testing the circuit with a spare sidelight bulb rather than using the meter. If that lights when connected direct to the switch you can be sure the switch is OK. Then try it at the bullet connector.

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1 hour ago, RobH said:

If the voltage disappears when you put a load on the wire, the problem is at the source end, not at the load. If there was a short at the bulb end you would blow the fuse and you haven't said that happens. As I said, I think you are being fooled by your meter, which can show 12v even though the connection is bad.

Try testing the circuit with a spare sidelight bulb rather than using the meter. If that lights when connected direct to the switch you can be sure the switch is OK. Then try it at the bullet connector.

Thanks! Will try that tonight!

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On 9/5/2019 at 1:36 PM, RobH said:

If you have already replaced the intermediate connectors it probably points more to an intermittent fault with the switch. ( I take it the main beams still work OK which probably eliminates earthing and similar problems at the bulb end which are also quite common.)

Thanks for the help..! Now fixed... The problem was indeed with the switch. I believed too much in the multimeter which measured 12v at the switch for dipped  lights..using my homemade bulb tester there was not enough current to light a low wattage bulb!

I have now learned not to fault find with a multimeter! Have replaced the switch from the one out of my TR4 for the time being until a replacement arrives and all is good..!!

 

 

20190907_102111[1].jpg

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I opened my original switch, as it had a high resistance. After cleaning and some vaseline all was ok again.

Better to have an original switch repaired than hope a new replacement will also last several decades. And so much more rewarding.

I tested, cleaned and tested every switch in my car during the restoration, and was surprised that several had high resistance due to fouling/corrosion.

Waldi

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  • 2 weeks later...
On 9/7/2019 at 4:01 PM, Waldi said:

I opened my original switch, as it had a high resistance. After cleaning and some vaseline all was ok again.

Better to have an original switch repaired than hope a new replacement will also last several decades. And so much more rewarding.

I tested, cleaned and tested every switch in my car during the restoration, and was surprised that several had high resistance due to fouling/corrosion.

Waldi

+1 for strip, clean and reuse an original if possible  

 

Peter W

Edited by BlueTR3A-5EKT
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