Turn lights on = power loss (as in affects engine) help?

If I turn on my headlights while accelerating, the transmission disengages for a couple seconds.

If my headlights are on and I turn the key/then remove it. The engine still runs if my foot is on the brake.

Weird I know, but just curious if anyone else has had this issue?
Im about to rip out the old alarm/remote start tomorrow which I believe is fried and could be the source of all these electrical issues... doesn't seem like it was installed correctly.
 

Eric Experience

Well-known member
Yes I do a lot of work on Sprinters that have had wiring added to them, The first thing I do is remove every mm of non standard wiring. And join up wires that have been cut. Eric
 

MillionMileSprinter

Millionmilesprinter.com
Yup. X2 what Eric said.
A customer of mine was replacing a tail light bulb and accidentally pulled out one of the wires from the tail light harness. He put it back into what he thought was the correct spot. Everything seemed fine until he went to turn off his van the same thing that happened to you, happened to him. He turned the key and pulled it out, but the engine kept running!
With an aftermarket alarm or anything extra, one grounded wire can easily cause the symptoms you describe.
 

autostaretx

Erratic Member
There have been other threads about "kept running" which ended up being damage/shorting in either the license plate light unit (or the wires leading to it) or the tail (usually brake) lights.

"Turned on the headlights" hints at a similar root cause (try just turning on the parking lights).

--dick
 
Thanks for the replies! Happy I'm not the only one with this issue... took out the alarm. That wasn't the issue. Im going to check the tail lights... I wired a trailer light hook up. Could that mess with the Transmission? / engine not turning off?
 

Nautamaran

2004 140” HRC 2500 (Crewed)
I wired a trailer light hook up. Could that mess with the Transmission? / engine not turning off?
My trailer wiring came from the factory, so lucky me! :thumbup:

The MB installation retrofit procedure is quite involved, but is designed to prevent the trailer lights overloading or corrupting the tail lamp circuits. I've read of lots of strange things resulting from the brake and reverse lamps back-feeding the wiring harness, and have plugged in enough dodgy trailers to appreciate the factory approach.

The "silver" standard is to use an externally powered harness adapter, powered from an independent fuse, and with triggers tapped into the signal, tail, and brake lamps. This will at least isolate the vehicle wiring from a trailer short or other overload.

The piggy-back type harnesses that simply add the trailer lamp loads on in parallel with the vehicle lamps should be avoided.

-dave
 

Eric Experience

Well-known member
That explains the problem, you have a short between the park lights and the brake lights, that causes the ecu to think you have the brakes on so it reduces power. You need to get the wiring done a bit more professionally. Eric.
 
Just wanted to give an update on the solution. The problem ended up being a short at one of the dome lights in my cargo area. Hard to explain but the metal strip on the dome light was bent and shorting out and some how that affected my transmission and headlights causing weird power loss. Ended up bending it back into place and no more issues.
 

kjg912

2006 T1N 2500
I've had this problem on occasion also - remove the key and it keeps running, then turn off the lights to kill the engine! I believe my problem is also in the trailer harness but I'll also check the tail-lamp assemblies!
 

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