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Soooo....
1. Replaced all trailer wiring. All now new and shiny.
2. Used multimeter, verified that the factory plug is wired correctly for Aus 7 pin.
3. Swapped bulbs in and out.
4. Result: Disco is seeing trailer, both indicators work, with dash trailer symbol. Check. Lower bulbs work as tail lights when I turn on Disco lights. Check.
5. Both lower bulbs stubbornly refuse to work when brakes are pressed. (and multimeter shows 12V on pin 6 at this point...).
Anyone got any ideas? I'm going to swap out both of the brake globes again, but they look fine to the naked eye. The wiring is all good, so I'm running out of ideas...
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2 Attachment(s)
Attachment 180973
If you are getting 12V at pin #6 when you push your foot on the brake pedal, then the problem MUST be in the trailer wiring.
Check if you are getting 12V at the contact point/s for the brake light globes at the back of the trailer. Check also that you have a decent earth connection from the body of the globe to the trailer and/or earth wire back to pin #3 on the trailer plug (I'm assuming that if these same globes are working OK as "parking" or "tail" lights - the earth connection should be OK).
Assuming that we are talking about conventional dual filament globes as shown below -
Attachment 180980
there will be two "contacts" in the base of the socket for each globe. One "contact" should show 12V when the parkers / tail lights are turned on, the other should show 12V when the brakes are activated. Earth for both circuits is common and through the side / body of the globe fitting.
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You've used "lower bulbs" twice, in the context of tail lights and brake lights. From that I *assume* that you've used dual filament 5/21W bulbs.
There are a number of issues that may be at play with the trailer wiring, but we've not got a lot to go on. Have you scratched out a diagram complete with colours and pin numbers?
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Why are you still using globes when LED trailer lights are as cheap as chips these days.?
LED trailer lights are far more reliable than the old school globe jobbies and they are waterproof to boot [thumbsupbig]
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2 Attachment(s)
In no particular order,
1. I'm still using globes in this instance because it came with them, and it avoids playing with resistors to let the D4 'see' the trailer.
2. Thanks for all the help. In the end it turned out to be 3 separate issues:
The original socket at the front was shot. Replaced it and all the wiring.
The LHS light unit had a weakened/misaligned terminal: the arrow is pointing at it.
Attachment 180983
This, irritatingly, didn't become obvious until issue 3 was identified - the bulb there was dead on the brake circuit... Once I swapped the globes, this became obvious.
All good learning, and the multimeter proved its worth about 12 times. That said, before I worked out the dodgy terminal, it was spooky to be getting a reading of 12V from the multimeter there (because I was pressing into both terminals), but then not getting a known good bulb to light up!
In closing, on my own today, so here's the assistant brake pedal operator...
Attachment 180984
worked very well if anyone ever needs to do the same.
(and I'll go LED in due course, just not wasting the supplied bits in the first instance...)
