Strange electrical problem, license plate light

[Shaun @ Tru6]

Right side license plate light is out on my 07 328.

New bulb, no love.
Swapped left good light fixture and bulb from other side, Nope
12.4 V on the left good side across Plug terminals
11.4 V on the right bad side across Plug terminals

Got two new BMW fixtures
Left side good of course
Right side no

Measured fixture terminals
No bulb = 11.4 V
With Bulb = 0 V

is the plug bad? or something else





Old originals, lines show check voltage

[Rusty Heap]

Bad ground. Sounds like you have a "floating" 12 vdc you can measure, but when put under load it goes to 0 v?

[1990C4S]

Where are you measuring voltage? On the connector? Or connector pin to a local ground?

Also, measure the bulb resistance in your hand, them compare that to the resistance read on the connector (bulb side) pins.

[Shaun @ Tru6]

Originally Posted by Rusty Heap

Bad ground. Sounds like you have a "floating" 12 vdc you can measure, but when put under load it goes to 0 v?

I think that's correct.

[Shaun @ Tru6]

Originally Posted by 1990C4S

Where are you measuring? On the connector? Or connector pin to a local ground?

Also, measure the bulb resistance in your hand, them compare that to the resistance read on the connector (bulb side) pins.

When I put the Fluke probes into connector holes, I measure 11.4

When I plug in the fixture, no bulb and measure across the contacts (pic with red lines), I get 11.4

When I put the bulb in, goes to 0

[1990C4S]

Check the resistance on the other side of the connector with the bulb in. I wonder if you have a short and the output is being turned off.

[908/930]

After the relay I think there is a connector for the two positive lines feeding the lights, the left side goes through and the right taps into it. Likely a bad connection there. Follow the wires back and see if you find anything.

[blucille]

isn't the left side just 8" away, why not string two new wires from the light that works to the one that doesn't?

[Shaun @ Tru6]

All good advice, going out again after work.

the wiring is mostly hidden in the truck lid. I will make a short ground connector from the left to the right.

[fastfredracing]

You need a good concrete chisel .

[masraum]

Originally Posted by fastfredracing

You need a good concrete chisel .

LOL! You caught me off guard with this one. Thank goodness I wasn't drinking anything.

[908/930]

I can lend you my Hilti TE-80ATC, that should open up body panels pretty quick so you can find the wire.

[Shaun @ Tru6]

OK, here's the scoop.

35 ohms across the bad side bulb

Attempted to bridge the ground wire connectors left to right but but my chisel collection was either 7" or closer to 9 so they wouldn't work, classic Goldilocks syndrome, needed 8" (that's what she said). So I made a temporary wire connection across the ground wire terminals, IIRC, grey is ground in German cars. Anyway, that worked perfectly. No need to bridge the brown wires.

I don't like those little clamp on splicers. What would be a good quality or factory way to make that connection permanent?

[pwd72s]

To answer your last question...19 minutes, well worth it.

https://www.youtube.com/watch?v=E_m8xf3vfYE&ab_channel=IrvinOrtega

Another option:

https://www.youtube.com/watch?v=dImF86OwiK8&ab_channel=electronicsNmore

[Superman]

Dark magic, obviously. Have you pissed off any sorcerers lately?

[1990C4S]

Originally Posted by Shaun @ Tru6

What would be a good quality or factory way to make that connection permanent?

That's like asking 'what oil should I use, and do I need ZDDP?'.

I always solder, tape, and then shrink wrap. Lots of people say that's a hack and it will fail. It has never failed me. I like to do a good wrap with the two wires, I think there is actually a NASA approved warp if you search.

Butt splices with a proper crimp tool are also good. I like the shrink wrap to hide the mess and keep water out.

I have a soldered and shrink wrapped connection submerged in my pool 24/7 on my robot, it is fine.

[Shaun @ Tru6]

Thanks, I have generally soldered and shrinkwrapped too. Ducati headlight last summer. Lot of vibration, still working fine. I like the connections Paul posted too.

[Tobra]

That sort of looks like the front of my wife's truck after someone stole the front off it

I always thought solder/shrink wrap was more permanent. Works better than the crimpy way, whether you have the right tool or not, seems to be pretty durable too