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Ignition always on?

Started by Feather535, 04 June 2023, 01:27 PM

Feather535

Well, I was about to declare victory and take my now running 280 SE to the smog station, but a new issue has surfaced.

I left the car outside yesterday and when I came back to move it into the garage, the battery was dead.  When I connected the battery to a charger, the fuel pump started running.  Weird!

After charging the battery the engine started normally, but it kept running after I turned the ignition off--even after removing the key.  I had to pull the fuel pump relay to stop it running.

I tested for current draw and something is pulling 7-8 amps, even with the key off.

This is a new problem for me, but maybe not for the list.  Has anyone seen this before?  Ideas about what could be causing it?

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1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Feather535

More on this.  I reasoned the problem must be in the ignition switch because nothing else could account for the engine continuing to run when the key is turned off and removed and parasitic drains that keeps the fuel pump operating with the key off. 

I removed the switch (the electrical part, not the lock) and tested continuity between terminal 30 (battery) and terminal 15 (run).  The circuit is open (no continuity), as it should be, with the switch in the off position, but current flows, as it should, with the switch in the run position. 

So what's happening?  Could it be the ignition lock?  Or a short somewhere else in the system?
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Feather535

I see people has been reading this thread, but no one has responded, so I'll give the conclusion of the story in case anyone else encounters this problem.

After removing the ignition switch and testing it, I found the switch was okay, but the current draw was still there with the switch removed.  That meant I needed find another component that is connected directly to battery voltage and to the run circuit.  There aren't many components in this car that are wired that way, and I discovered that whatever was causing the problem was drawing current through fuse 4. 

To make a long story short, it turns out to be the hazard switch.  The wiring diagram shows that it is connected to the battery bus and the start-run bus. So a short in the switch was causing current from the battery to feed back into the run circuit even with the key turned off and removed. 

An easy enough fix to remove the switch; it has never worked since I've had the car.  But I probably need to find another switch.

--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

BigGreenMachine

Good find!

What are the components you know of that are wired always on? I disconnect my battery between drives because it will usually run down over a period of weeks to months. I've always just assumed it's the clock since I can hear it ticking away from outside the car (when the garage is otherwise silent), but must admit I don't know what other components are able to draw when the ignition's off.

Feather535

Quote from: BigGreenMachine on 06 June 2023, 11:09 PMmust admit I don't know what other components are able to draw when the ignition's off.

There aren't many.  I believe the clock is the only component that is "always on."  A few other components draw from the battery but are switched.  The ones I know of besides the flasher switch are the interior dome lights, the trunk/boot light, the electric windows, the power antenna and of course the main light switch.
--------
1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)