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Joined: 20 Mar 2007
Posts: 431
Location: Cambs

PostPosted: Sat May 06, 2017 9:11 pm    Post subject: Under bonnet courtesy light Reply with quote

Im trying to trace a parasitic current draw on my battery which has suddenly started running down quickly if I leave the car parked for a few days .

I'm starting by testing the battery drain under the bonnet but just realised there is an under bonnet courtesy light which might be drawing current so I need to make sure it is switched off whilst I've got the Bonnet open .

But stupidly I can't find the switch anywhere. does anybody know where it is Please?
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kerb scraper

Joined: 25 May 2012
Posts: 329
Location: Hertfordshire

1997 Porsche 993 Carrera 4

PostPosted: Sat May 06, 2017 9:30 pm    Post subject: Reply with quote

Just click the latch over to the closed position using a screwdriver or similar.
1997 C4 Cabriolet, Arctic Silver, black interior, 18" hollow spokes, Bilstein PSS10s, RSRs, 200 cell cats, Mobil 1 sticker, LED to interior. Bergville t-lights.
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Joined: 02 Apr 2017
Posts: 14

PostPosted: Sat May 06, 2017 10:33 pm    Post subject: Reply with quote

Are you sure your battery is not on the way out especially if you have to turn off the light when the bonnet is open?

If the problem is irregular use of the car then I can recommend the battery isolator sold everywhere which is fitted to the negative terminal and consists of a wheel which you give a quick turn if and it isolated the battery. It can be fitted in minutes and is sold as an anti theft device.

Remember that unless your car is parked somewhere secure it also isolates the alarm unless you install the fused link which gives a trickle of power to the car.... thereby rendering the whole purpose redundant.
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Joined: 07 Apr 2008
Posts: 72

PostPosted: Sun May 07, 2017 6:31 am    Post subject: under bonnet curtesy light Reply with quote

i take the bulb out .its only for the fuse box . I carry one of them cheap wind up torches in case of emergencies
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Approved Trader

Joined: 13 May 2010
Posts: 518
Location: Oslo, Norway

PostPosted: Sun May 07, 2017 7:43 am    Post subject: Reply with quote

The most probable cause for excessive current drain is failing door switches. These does not only activate the interior lights, but a relay or two as well as the alarm/door lock control module. Turning off the interior lights masks this problem.

Another common problem is a failing on/off transistor in the Climate Control Module. This can leave the unit on. (it is supposed to shut off in 20 minutes after ignition off) However, this is normally about 500mA due to the CCU fan. However, if the fan has failed you could get about 100mA. Pull Fuse 1 to test.
The tachometer OBC LCD backlight circuit can fail to shut off when car is locked, this is also a probable cause for this current rating. Fuse 12.

Be sure to measure the current with all interior/bonnet/engine lights off, lock the doors, and wait for the CCU to turn off. The light switch in the luggage and engine compartments are placed in the lock mechanism. Depresss the latch to switch off the light.
You might consider opening the windows first to avoid having problems getting in due to a problem with immobilizer or similar.
Normal current draw at ignition off is normally around 20-25mA. Depending on aftermarket equipment installed, (alarms/stereos etc) this can increase to 30-40mA.

'95 993 C4

Bergvill F/X
Porsche electronics specialists, products and repair services.
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Joined: 25 Mar 2010
Posts: 1267
Location: The fast lane

PostPosted: Sun May 07, 2017 9:07 pm    Post subject: Reply with quote

As Kerb-Scraper suggested - just flick the catch when the bonnet is open, and pop a rag in it so you don't forget to release it.
However, I'm wondering if you actually meant "whilst I've got the Bonnet closed...."
If this is the case, you can tell when you lock the car, as the alarm will report a fault when you lock it, by flashing the door LED's twice per second instead of once per second if one of the interior, bonnet or engine lid light is still lit.
1996 Polar Silver 993 Coupe
A Class AMG for the DD
ex - 996.2 C2, 986.2, 996.1 C2

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