Battery drain, interior backlights

[natejgreene9871]

I wanted to start a separate thread for this. I have a 1993 400e and have a battery drain issue. The backlights for the window switches, gear selector, and switches above the hvac (recirculate, or headrest lower) stay lit up. It slowly drains the battery.

I have replaced the headlight switch, no luck. All fuses are clean.

Dome light works correctly and turns off with timer, it is just the backlights on the switches.


Any ideas? Who is good at looking at wiring diagrams? I assume there is a relay somewhere that’s not deactivation properly?

 

[gsxr]

IIRC there is another component in the backlighting circuit. Probably need to look at the schematics in the ETM. I vaguely recall this being discussed a few years ago but the symptom was different, IIRC?

 

[Jlaa]

I wanted to start a separate thread for this. I have a 1993 400e and have a battery drain issue. The backlights for the window switches, gear selector, and switches above the hvac (recirculate, or headrest lower) stay lit up. It slowly drains the battery.

I have replaced the headlight switch, no luck. All fuses are clean.

Dome light works correctly and turns off with timer, it is just the backlights on the switches.


Any ideas? Who is good at looking at wiring diagrams? I assume there is a relay somewhere that’s not deactivation properly?

There is a big long thread here somewhere with @Kyiv diagnosing issues with his switch backlights. There were a lot of electrical diagrams in that thread. That thread, when you find it, should help.

 

[natejgreene9871]

I found a thread on Benzworld that is similar.

i found what was draining my battery but need some help

...92 300e i put in a new interstate battery manufactured 12-2012 but after a couple of days of not driving that car the battery went dead. i do have this huge (thick) wire on the positive side of the battery probably for an amp so my thought was to disconnect that, then i went outside before...

www.benzworld.org

Leads me to believe it is the instrument lighting control unit

004 545 08 32


Right behind the instrument cluster


Going to order one and see how it goes

 

[natejgreene9871]

more curious behavior with this relay module. When i first bought my 1993 400e a couple years ago it had the battery drain issue. After driving the car on a daily basis it resolved itself.

Now it has come back. Backlights are on all the time and draining the battery.

I sourced a used light relay module from a 1993 300e, it is internally very different but pin outs are numbered the same and it appears to function the same?

Why would V8 cars of the same year have a different module?

• 300e part number is 004-545-08-32 (not sure of brand?)
• 400e part number is 003-545-63-32 (VDO branded)

Perhaps the VDO in the V8 cars is the newer part number? It has about twice the circuit board area and a larger heat sink.

Here are photos to compare.

I do wonder if changing the capacitor on the VDO unit would fix it.

Any thoughts on the differences here?

 

[gsxr]

In the EPC:

003-545-63-32 shows only for early (1986-1989) 124 chassis.
004-545-08-32

And, there is a supercession from early to late:



They should be functionally equivalent.

Are you sure this is the root cause of your power drain?

 

[natejgreene9871]

In the EPC:

003-545-63-32 shows only for early (1986-1989) 124 chassis.
004-545-08-32

And, there is a supercession from early to late:

View attachment 223791

They should be functionally equivalent.

Are you sure this is the root cause of your power drain?

Interesting. Yes I am sure. I have swapped between the two and the issue immediately goes away once I install the 004 part number.