Kudos to Jim for confirming the pull up voltage theory! I believe there has been a comedy of errors that led to this situation:
1.) The voltage at the 7 pin socket is a “pull up” voltage from the SAM and won’t carry any current to speak of. 2.) This voltage, while minimal, was enough to light the LEDs in the adapter socket, which would explain why they were lit for the turn signals when the signals weren’t on. 3.) The UHaul trailer, despite what the lot guy told me, almost certainly had LED lights. 4.) The circuitry in the SAM has “lights out” functionality much like it does for any other light on the body. This means it wouldn’t have played nice with LEDs in the circuit unless there was a load resistor somewhere. How did I confirm? A tried and true and quite antiquated approach - an 1157 bulb as a test light. When connected to the appropriate terminal on the 7 pin socket, would light up and perform as expected for turn signal, brake light or running lights. So I burned maybe 90 minutes and five pounds of sweat chasing this down, but now I have a better understanding of the system and discovered the location of a number of different components on the car. And I got a full diagnostic scan on it as well, showing almost 100% check marks, which is always nice. I finished my time up with a good Martha’ing on the interior with the shop vac, and even found a little bit of cruft in the cowl vents I had missed that has now been vacuumed out. Lesson learned. I need to find an adapter that will allow the use of LEDs in the trailer harness. Time to play inside for the rest of the day and enjoy the AC. -D > On Aug 13, 2022, at 4:10 PM, Kaleb Striplin via Mercedes > <[email protected]> wrote: > > The u haul trailer we rented a while back was all LED. Everyone I have seen > for a long time has been. Even with that it worked fine with our GL. I’m > wondering if someone installed the resistors or whatever is needed on mine to > make it work. > > Sent from my iPhone > >> On Aug 13, 2022, at 2:40 PM, dan penoff.com via Mercedes >> <[email protected]> wrote: >> >> Thanks for the insight, Jim, I was wondering this as well since the SAM >> drives it directly. However, when it was plugged into a “real” trailer we >> still got nothing. >> >> I’ve got an 1157 lamp with some leads soldered to it - I’m going to try that >> on each terminal and see what happens. >> >> Everything else has checked out. Now I’m wondering if the UHaul trailer >> *did* have LED lamps, as these do not work with this system for the same >> reason as above. I asked the UHaul guys if the trailer lamps were LEDs and >> they said no. Hmm. That would also explain why the diagnostic LEDs were lit >> on the adapter - it would only take a a few mA to drive them. >> >> More as I know it. >> >> -D >> >>>> On Aug 13, 2022, at 3:07 PM, Jim Cathey <[email protected]> wrote: >>>> >>>> And there is still power to all terminals at the 7 pin socket (except for >>>> trailer brake and ground.) >>> >>> Power? Or +12V measured with a multi-megohm input impedance meter? >>> (Zero current, essentially.) Chances are it's got a pullup system, looking >>> for >>> the load of bulbs to draw signals to ground so that the car can do lamp-out >>> checking, and trailer-plugged-in checking, etc. >>> >>> -- Jim >>> >> >> _______________________________________ >> http://www.okiebenz.com >> >> To search list archives http://www.okiebenz.com/archive/ >> >> To Unsubscribe or change delivery options go to: >> http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com >> > > > _______________________________________ > http://www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > To Unsubscribe or change delivery options go to: > http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > _______________________________________ http://www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
