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Driver rear tail light dimly lit when car is off

Rik

Member
Sep 12, 2013
142
0
Northern VA
I've found that my 2.0 driver side rear tail light remains dimly lit (no other lights on and does not matter if light switch is on or off) after the car is off. it will remain on until it finally decides to turn off... this occurs randomly and can do this for days. No real impact on battery.

Here's a photo of what it looks like. Unless it's completely dark, I typically have to cup the light with my hands to see if it is the reason my rear fan is running.

SC has looked at this a couple of times over the past several months. Last visit to Tysons was a 2 week stay where their best guess was a faulty tail light. They said they could not reproduce and that supposedly there was no power draw the entire time it was with them. I'm at a loss and concerned more about what else may be awry and the longer term impact on power draw.

Anyone seen anything like this?
Toughpad - 1.jpg
 

Chickenlittle

Banned
Sep 10, 2013
2,781
4,943
Virginia
I've found that my 2.0 driver side rear tail light remains dimly lit (no other lights on and does not matter if light switch is on or off) after the car is off. it will remain on until it finally decides to turn off... this occurs randomly and can do this for days. No real impact on battery.

Here's a photo of what it looks like. Unless it's completely dark, I typically have to cup the light with my hands to see if it is the reason my rear fan is running.

SC has looked at this a couple of times over the past several months. Last visit to Tysons was a 2 week stay where their best guess was a faulty tail light. They said they could not reproduce and that supposedly there was no power draw the entire time it was with them. I'm at a loss and concerned more about what else may be awry and the longer term impact on power draw.

Anyone seen anything like this?
View attachment 93637
Funny have noted the same in my 2.5 roadster. Same light. Wasn't sure it was really on, so faint. Just went through annual service and inspection. I had forgotten to mention it. If you find out issue let me know please
 

Rik

Member
Sep 12, 2013
142
0
Northern VA
My guess is a mosfet in the switchpack is not fully turning off from time to time.

That's greek to me but I'll pass along to the SC. Thanks!

- - - Updated - - -

Funny have noted the same in my 2.5 roadster. Same light. Wasn't sure it was really on, so faint. Just went through annual service and inspection. I had forgotten to mention it. If you find out issue let me know please

Which SC did you go to for your annual service? I will want to raise the point that you are experiencing this too. So far, I cannot relate when it happens to charging, temperature, charge settings, cool downs, charge port open or closed, last door opened... nothing.
 

Chickenlittle

Banned
Sep 10, 2013
2,781
4,943
Virginia
That's greek to me but I'll pass along to the SC. Thanks!

- - - Updated - - -



Which SC did you go to for your annual service? I will want to raise the point that you are experiencing this too. So far, I cannot relate when it happens to charging, temperature, charge settings, cool downs, charge port open or closed, last door opened... nothing.
Tyron's corner/ tyco rd. looked last night, not on anymore but it was intermittent in past. Light not bright at so subtle I at first thought it was reflected but not
 

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
5,715
11,988
Hickory, NC, USA
Almost definitely a fet partially stuck partly closed. (A mosfet is basically a digital relay/switch with no moving parts). Is that light LED or an incandescent of some kind (I'm not familiar enough with the roadster)? If it is the latter then it wouldn't surprise me if the mosfet is leaking a little after years in service since it would be handling a slightly inductive load. The flyback diode may have also weakened over time and accelerated the wear on the mosfet, or may not exist entirely depending on the design.

Basically it is probably more trouble to fix than it's worth. It's literally a $0.25 part on a circuit board that is likely inside a larger module that is way more expensive. If the amount of current leaking is negligible, I'd probably leave it alone. If it gets brighter over time... well, then you're going to have to look into a repair probably.
 

bigbill

Member
Sep 29, 2012
36
18
Silverton, OR+Hana,HI
My guess is a mosfet in the switchpack is not fully turning off from time to time.

That's a good possibility. Another is that some water made it onto a PC board. This can cause oxidation, which can create an intermittent path with resistance across some of the traces.
Another possibility is a strand of wire has broken off of a connector at the crimp and is sometimes contacting the connector next to it.
 

Timothy

Driving on Sunshine
May 4, 2011
431
114
Mine did this too for months--then healed itself before I had the car serviced 2 years ago! Hasn't happened since.
 

jimmyz80

Member
Dec 26, 2014
476
339
El Dorado Hills, CA
The service records for my roadster indicate that it had this problem early in its life. I believe the "fix" was replacing the tail light. From reading this thread, it seems to be more common that I would have expected.
 

mookhead

Member
Jul 17, 2014
109
146
SF Bay Area
I should have followed up on my experience...

After replacing the switchpack, the problem re-occurred (or never went away, it's hard to see), so days before my extended warrantee expired, I took it back to the Fremont SC, whereupon:

1. 7 days into it, "we can't reproduce". I drove over, pointed at the problem, they went "ohhh", got back to work.
2. 2 days later, they call me to tell me they need replace my PEM
3. 24 days later (!), they install new PEM
4. 2 days after that, they call me to tell me it wasnt the PEM after all, and that they installed a new tail light and that fixed it.

Sheer comedy.
 

Roadster

JdeMO Powered
Dec 10, 2016
1,541
1,229
SoCal
Bumping this thread to see if anyone else has this faint glow from the driver's side rear fog light.

Sadly, in the U.S., we don't even have a rear fog light switch (though... if anyone in Canada, the EU or HK has access to a donor with all the parts & components to retrofit it, definitely PM me) so is there any harm in simply disconnecting it? Granted, the current draw as noted above is minimal, and I certainly don't want/need spend the $$$ to replace the entire taillight assembly just for this, but is the problem even something user-serviceable or shall I just accept it as a quirk of the car?
 

DeedWest

2008 VP & 2011 2.5 Sport
Feb 5, 2014
877
927
Dallas, TX
My 2.0 has done this since I’ve had it, as well as the two 2.5’s I owned before it. It never bothered me enough to pursue getting it “fixed”. Doesn’t seem to impact battery life or anything else negative.
 

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