Parasitic electrical loss

[grendiers]

Finally, after 10 years of ownership of my 1989 944 turbo, I decided to find out what is draining my battery. Turns out, pulling fuse 8 and 11, dropped the drain from .07 and to .03 on the 10 amp setting of my meter. Pulled the rest of the fuses, and it stayed at .03.

Number 8 is for central locking system and relay sunroof. Number 11 is for the following:

Interior light, trunk light. Neither one works all that well.
Cigarette lighter, gear indicator.
Glove compartment lighter. Not sure if they mean light.
Buzzer contact-gong relay
Clock, which doesn’t work, and diagnosis plug.

Where to start?

[Chalt]

I can't chime in on what specifically might be draining it. I would imagine pulling one fuse at a time may lead to the answer. But in other threads, people have said that some parasitic loss in these old 944s is not unusual.

Since mine isn't a daily driver, I keep it on a Deltran Battery Tender. It keeps the battery charged but doesn't overcharge or boil the liquid out of the battery.

This may not be what you want to hear, and isn't the only solution, but it is a solution that works.

[grendiers]

Well, number 8 and 11 are the culprits. I checked them all.

[944 Ecology]

If you pull fuse 8 and leave fuse 11 in, what is the draw?

If you pull fuse 11 and leave fuse 8 in, what is the draw?

If fuse 11 is the problem, start disconnecting each of the suspected bulbs/indicators/relays.

Check the draw after each removal. Keep notes of how much the draw changes.

It's not rocket surgery, after all.

[Monkey Wrench]

near the fuse , are there some terminal connections? other wires being fed by the same shared fuse? you could try unplugging wires there, maybe help isolate the one with some draw.. then look at the colors on the schematic. even a busted clock probably draws power, and its right twice per day! likely the gears are stuck but the electromagnetic coil that drives it is still probably connected so might still draw the same power. in my Volvo it clicks about once per second much like the battery movements on common wall clocks.

I guess you could stick a battery clock movement in there maybe with a battery holder attached where it's not so hard to access, if you dont want to spend on an OEM clock. setting it might be a challenge since you couldn't reach the hands to push it. the actual clock movement could be common to a bunch of cars. my volvo 740 has a big one, so does my 240 and they miraculously work fine.

I had a car with a cheapo dollar store type stick on LCD clock, the thing worked for years without a battery, nicer to make it right.. but if you just dont want to keep looking at your phone when driving, maybe that's a cheap option just so you have a clock.

sounds lie you are on the right track, if you can eliminate down to the fuse you can narrow it down more, you just need access to the wires that that fuse feeds.. You obviously know how to isolate it and check the draw so its just a process of elimination to find the culprit. first place I'd look for the junction is any spade connectors right behind the fuse, likely some shared terminals there.

central locking system might be intentionally confusing there is some info on the garage site about bypassing it, and I think its around behind the glovebox somewhere..

no idea where the sunroof relay is, someone will probably know. maybe the factory schematic has a relay location guide? I know in Volvo they stuck relays in some pretty weird spaces, a lot of times you have to know where they are otherwise they can be a nightmare to locate but there are published diagrams that seemed to change frequently with updates, accessories etc. Often the relay for a motor is located physically close to the motor to save wire length. the coil that activates the relay is low amps so likely a small wire, and then its connecting basically power to the motor of larger amperage so likely you'd have larger wires for feed and for what the relay is doing, if it draws a lot.

some relays have a holding circuit and a pull in circuit. I can't think of one in the Porsche like that , an example is the relay used in a volvo overdrive it has a coil to pull it in and another coil of less amps to keep it in place. the reason for the holding coil is to reduce the constant amp load once the mechanical movement takes place by the larger pull-in winding.

I was murking about under the hood of my volvo the other day had left the key on, reached near the idle air control valve. i think some Porsche 944's used the exact same part. this one has 3 pins. it was vibrating.. weird I thought..
so i swapped it out after cleaning up a spare I had onhand. sometimes I see solenoid valves used in other equipment, that maybe have some play around the pull-in spool, I think they wear out from vibrating.. I just replace the solenoid when I find that and it fixes the issue.
In AC wiring, it seems reasonable but in a car it's DC power, so I'm not not sure why they would vibrate. It surprised me that the ICV did that. I guess in that car with the key on, and the throttle closed power must be fed constantly to keep the ICV in a certain position. I do not know why it needs 3 wires to run a solenoid, maybe it pulls both ways or has some sort of mid position, or something. I once had my volvo parked and had left it key on I found the coil got pretty hot and wondered why, I figured it must have some significant draw through the coil even when stopped and with key on. maybe it could wreck the coil, it was pretty hot but didn't seem to fault or anything.


anyway the checks you are doing are with key off so its probably not live anyway. any you probably need some more specific info on the relay location. at least for the sunroof motor.

one circuit that can draw power with key off is the parking light circuit.

in my volvo I found I could pull the speedo, then through that hole it was very easy to disconnect the key , it unplugs, the end of the harness there has a round plug with a bunch of contacts.

the key has some heavy red wires feeding it. seat heaters and headlights are disconnected when key is turned to start so that the starter isn't having a power struggle against the seat heaters or headlights. that is dome in my Volvo by the key switch contacts, not a relay. there is one wire there feeding things that need constant power, so if the porsche is at all similar maybe by pulling the key switch that might give access to a fairly main part where it may be led off to other locations. if you probe there you might find a wire that feeds stuff with the key in the off position.

if you have a key behind the door to unlock the central locking system, that's basically a switch. it would stand to reason that is a circuit that is always alive..
it maybe open circuit until the "disable alarm" key is turned, but it needs power ( at the ready) to activate whatever it is doing, so that must be a live circuit with the key out, maybe similar for power door locking systems. they too have to activate in the key off position to perform their function.. so those must involve some hot wires with key off..
maybe chasing down any source of draw could result in finding some wire rubbing or similar?

sometimes people installing car stereos may decide they want the radio to work with key off, maybe you want to be able to turn the radio on while you work on the car, without leaving the key on for example.

so someone might go looking for a wire that is hot with the key off. that might lead a constant power source into some crappy connections because people who install car sterios dont always understand that much about how car wiring works or how to do proper connections, maybe the radio needs a constant power to keep programmed stations in memory.. on some cars disconnecting the battery looses all the stations or in some sterios it may require a code to work after disconnection.

my volvo has a power antenna, so it is fed power to do that after key off, another thing it can do with the key off is to keep the interior light on for 30 seconds or so, then it shuts off. so that's some extra wiring that's always live, even with the key out.

I know the porsche isn't at all a volvo but there may be some similarities you could grasp ideas from. similar area , similar technology, the Swedish and German factories weren't that far away from each other technically. mostly all Bosche parts. in Europe it is common to use parking lights, and leave them on because streets are crowded and they park halfway on the sidewalks, not a common practice here.

someone here pointed out that in a Porsche if you put the signal switch to the left turn signal position and park the car with the indicator lights on, it powers only the left two lamps, or I guess the reverse is true.. I guess it saves the battery life a bit by not running the other two bulbs. Perhaps that may be an extension of wiring that is live all the time.

I always thought it odd that they wouldn't make the horn work with key off, it happens where someone is sitting in a car, even on passenger side, and maybe someone tries to back into you and it would be nice to be able to honk the horn but you don't have the key in. by the time you fix that in order make the horn work the event is over. the horn isn't a big power draw, unless its stuck ;-)

.

[kdjones2000]

I blame your clock....

In my experience the radio is the highest source of current draw in our cars, everything else working as it should.

[Monkey Wrench]

do the stock radios have a security code that needs to be reset if it's disconnected?

[Jfrahm]

Glove box light, often falling apart, can be a problem.
I have also heard of the clock failing and becoming a drain.

[originalowner]

http://www.clarks-garage.com/pdf-manual/elect-26.pdf

[grendiers]

Originally Posted by kdjones2000

I blame your clock....

In my experience the radio is the highest source of current draw in our cars, everything else working as it should.

Car came with a spare clock. I saw a video on how to replace it. Looked like a bit of a job as I recall.

[grendiers]

Bench testing the replacement clock. Modified a trailer light plug, insert brown wire to ground, #31. Green wire to power, #30. Clock works!

[Jfrahm]

Clock is easy to swap.

[kdjones2000]

Just remember to twist that round vent piece before trying to remove it, or you will break things. There is a screw under it you have to remove to get the trim piece out.