1985 (late) 944 with battery issues

[hornetdriver]

My 1985 1/2 Porsche 944 seems to be eating batteries. Only drive the car once a week but the car has a brand new Interstate battery in it - new alternator. I tested the battery when I installed it - checked in at 12.8 - good to go. Started the car - voltmeter read 14.5 so alternator is doing it's job. Drove the car last week - no issues. Tried to start it a week later - Completely dead - couldn't even jump start it with my SUV. Suspect something is draining this battery big time. Anyone have a similar problem? Owned this car since it was new and have never had this bad a problem with the battery....

[marko]

Go to Clark's garage. Garage shop manual> battery>Excessive Battery Discharge Rate. It says it should be less than 65ma but I think it should be more like less than 20ma. Also have everything off and the doors closed.

Clark's Garage Home Page

[FransB85]

and check for clicking relays when unhooking and reconnecting the battery terminal (doors closed). a faulty relay can stay 'live' when the battery is on, but will not when you put the amp meter between the battery terminal and the wire. This means you won't measure a draw, but as soon as you reconnect the wire to the terminal, it's draining your battery.

[PorscheChef]

This might sound crazy, but...
I had the same issue on my 87 n/a. Tracked down everything to the point where I thought it could only be the DME. When I went to pull out the DME i found that there was a ton of ice in there. I found the standard leak in the battery tray, patched it and dried it all out. Checked the DME to see if it was damaged and couldn't see a cracked board or anything else wrong with it. After I put it all back together, it has worked great. So was the moisture causing the computer to foul out the battery? It seems like it was.

[hornetdriver]

Thanks for the ideas folks. Is there any way to test a relay other than to buy or borrow a known good one? My cooling fans are not currently working so it could be I have a bad cooling fan relay which could possibly be causing the drain on the battery? I have tried to remove the thermo switch connector to test the fans by bypassing the switch but it is very difficult to access.

1985 Late Guard's Red 944 125K miles

[hornetdriver]

Thanks for the information folks, I found that my fog light relay was draining the battery - Clark's garage troubleshooting guide was right on the mark! Now on to my cooling fan problem....