1986 Carrera battery drain

[FloydPink]

Hey Pelicans,

Been troubleshooting a battery drain in my 1986 911 lately. With all fuses installed, negative ground disconnected, and test light in series, my test light was well-lit. After removing fuses one by one, I narrowed most of the drain down to the clock/interior light/glovebox light fuse.

However, even with that fuse removed, there’s still about 200milliamps of draw - I removed all remaining fuses one by one and could not eliminate it (including engine compartment fuses).

I’d like to try to fix the issue on my own before paying for the professional’s help, but I’m pretty unfamiliar with what else could be causing the drain. Any ideas or tips for hunting down the remaining drain?

Thanks

[mo-mon]

On my '88, it was the door-interior light connection. I replaced the switches & it was gone. I also replaced the glovebox switch.

[Oneredspyder]

I have a similar issue with my 86 Carrara. Battery drain in about 4 days. Everything works on the car as it should. I have replaced the alternator and turn signal switch in the past 2 years. I hooked a volt meter between the ground and the battery and it read 13.4 volts. Pulled each fuse and each relay under the frunk and the 13.4 volt reading never changed. What’s up?
Thanks

[John W.]

Connect your VOM between battery negative and chassis ground with the VOM in ammeter mode. Then you can pull fuses and see when the current drops. That will be the circuit where your current drain is. There could be more than one. Good luck.

[darrin]

does your interior dome light still turn on when your driver's door is open/off when your driver's door is closed? Can you operate your power windows when your driver's door is open? On my '86 targa, the door dome light switch also triggers a relay that cuts power to the power window circuit after a door is opened -- as Mo-mon indicated above, if the driver's side dome light switch is inoperative (they can build up corrosion), the power window circuit remains energized, slowly draining the battery. Easy to fix/replace

[49willard]

Are you leaving the key in the ignition?

[MRCarrera]

I had a similar problem, in my case it was the light in the front bonnet that probably didn't switch off automatically.

[FloydPink]

Thanks for the suggestions all. Some answers:

1) The dome lights do turn off when I close the doors.
2) I’m not leaving the key in the ignition.
3) I checked the front bonnet light and the bulb is missing, previous owner must’ve removed at some point.

Developments:
I’m fairly certain my multimeter is busted. It’s the one my dad has been using for years so it probably crapped out a while ago. Going to order a new one soon.

However, I did notice that the windows have power at all times - doors closed and key out of ignition, doors opened and then closed and key out of ignition ignition, doors open and key out of ignition - it all works. Could this still be caused by faulty door switches even though they turn on/off the dome lights properly?

[darrin]

Originally Posted by FloydPink

Thanks for the suggestions all. Some answers:

1) The dome lights do turn off when I close the doors.
2) I’m not leaving the key in the ignition.
3) I checked the front bonnet light and the bulb is missing, previous owner must’ve removed at some point.

Developments:
I’m fairly certain my multimeter is busted. It’s the one my dad has been using for years so it probably crapped out a while ago. Going to order a new one soon.

However, I did notice that the windows have power at all times - doors closed and key out of ignition, doors opened and then closed and key out of ignition ignition, doors open and key out of ignition - it all works. Could this still be caused by faulty door switches even though they turn on/off the dome lights properly?

Sounds like you've found the source of your battery drain -- wondering whether you might have an issue with the power window relay itself, instead of the door switch triggers? The door switches are simple, single wire, switches -- if the driver's side door switch is turning off the dome light when the driver's side door's shut (important detail), then the problem's not with the door switches. Since the door switches (are supposed to) trigger the power window relay to deactivate the power window circuit, checking/confirming that the power window relay hasn't failed would make sense as a next step.

Other question/thought -- does/did your car have an alarm installed? could be that the alarm highjacked the door switches for security monitoring purposes or otherwise messed with this wiring?

[GH85Carrera]

If the car ever had or has an alarm, it is very likely the culprit. Most alarms were put in by hacks that did not care at all about proper wiring procedures. And they sure did not use a wiring diagram from Porsche.

I can leave my 85 911 sitting in the garage for 5 or 6 weeks and it has lost very little or no charge. In the dead of winter, when the garage is cold and the weather outside is frightful (like this year's crazy February) I plug in the battery maintainer. If it is likely I will be driving in a week or two, it just sits in the garage, under a car cover, waiting on me.

[darrin]

Originally Posted by Oneredspyder

I have a similar issue with my 86 Carrara. Battery drain in about 4 days. Everything works on the car as it should. I have replaced the alternator and turn signal switch in the past 2 years. I hooked a volt meter between the ground and the battery and it read 13.4 volts. Pulled each fuse and each relay under the frunk and the 13.4 volt reading never changed. What’s up?
Thanks

Oneredspyder -- you need to measure current (amperage), not voltage -- while a significant power drain (e.g. headlights) will cause a significant voltage drop, a small draw (which takes 4 days to drain the battery) will not.

[darrin]

Floydpink -- here's a link to another thread involving issues caused by the power window relay that will help you locate/test it. Power Window No Power at Fuse#1

FWIW, when my door switch failed (and was allowing the power window circuit to remain active as you determined yours is), my battery would drain after 4-5 days of sitting. After fixing the door switch, my power windows would no longer operate after a door was open and '86 Carrera can now sit for for a month or so w/o issue.

[Oneredspyder]

Hello all. I really appreciate the input here. I realize that I do have gremlins in and about the dome light switch and the power window switch. I have replaced the passenger window switch twice. So my plan is to buy some switches and relays and go from there. I will check ohms, not voltage. I appreciate the suggestions and will reply when I sort it out.
Thanks.

[Oneredspyder]

Hello all. I really appreciate the input here. I realize that I do have gremlins in and about the dome light switch and the power window switch. I have replaced the passenger window switch twice. So my plan is to buy some switches and relays and go from there. I will check ohms, not voltage. I appreciate the suggestions and will reply when I sort it out.
Thanks.

[darrin]

oneredspyder, if your driver's side dome light switch doesn't work (turn on/off your dome light when the door's opened/closed), it's letting your power window circuit stay activated (and drawing power) while the car's sitting, which will cause the drain you're seeing. In my case, my passenger door's dome light switch was still functional (when the switch turns on the dome light it causes the power window relay to deactivate the power window circuit), so I was able to confirm the problem by opening my passenger door (and trip the circuit) to confirm that my battery drain ceased and that this was the source of my problem

[FloydPink]

I’m out of town for a few days but will pull the power window relays to check for current drop once I’m back. From what I’ve read it seems there are 2 separate relays; one circular relay above the fuses, and another square/cube one behind the gauges. I’ll check both of these, but wondering what the difference is between the two?

Whatever is causing the drain, I’m fairly certain it is not fused circuit (pulling all fuses did not reduce current draw). I’ll have to dig around to see if the car has an aftermarket alarm system as well, the car is still relatively new to me and I’m not sure if one of the PO’s had something installed.

[FloydPink]

Just got around to pulling the power window relay and sure enough that was it! Current draw from battery after removing the relay is ~30mA, nicely within spec.

Time to buy a replacement - it looks like the one pelican carries is 944.615.116.01, as the original relay ending in 00 is NLA. Looking at the pictures though, it seems that the 01 relay has different contacts than the 00. Has anyone installed the 01 in their 911? My gut tells me that it won't be compatible since it's missing the copper contacts that my 00 relay has on the bottom. Link to pelican's 01 relay.

Pics of the relay I pulled from my car:

[gomezoneill]

Good job

[darrin]

Floydpink -- think you'll be fine with the -01 -- the silver metal blades are all that should come into contact with the relay socket -- the copper pieces you reference look to simply be tabs holding relay components onto the base and not contacts for the socket (should be easy to confirm/disprove by looking closely at the socket itself)

[FloydPink]

Thanks darrin, I checked closely with my endoscope and it looks like I should be fine with the -01 relay. Ordered it and will follow up here if it works.