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Discussion Starter · #1 ·
Ok - my sons '88 900S is suffering from a case of battery drain. We've isolated it to the circut that the radio is on - but it's not the radio or the radio (aftermarket) wiring. The radio has been removed and, if the fuse for that circut is left in the battery continues to drain. Just a quick question to those with a more intimate knowledge of the Saab 900 wiring system than mine - is there a common area of failure on this circut that we should examine first?

I'd really like to get this resolved - he's getting really frustrated by his 900 and, as it's in otherwise superb condition - I'd hate to see him give up on it.

Thanks in advance

Steve
 

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steve, disconnect the alternator overnight and see what happens, i had a bad problem with engine cutting/ lights diming and radio flicking, it was the bit on the back of the alt shorting out now and again, might be completely wrong, but where mine was whilst running, i seem to remember someone saying it can drain out the battery as it creates a direct short, when car switched off.
why the radio seems to take the offence easily might be because it's probably(?) the lowest power item so it hits it first
 

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I presume you've traced the wiring back as far as you can from the radio already? Does anything else lose power when you pull that fuse? As standard, I don't think theres anything else on that circuit. Someone must have been in there - you may need to pull a good bit of the dash to figure it out.
 

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Check the trunk light, you can leave the rear seat back down so you can look.
If you have passive belts, remove those fuses.
 

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Discussion Starter · #6 ·
Jim Mesthene said:
Check the trunk light, you can leave the rear seat back down so you can look.
If you have passive belts, remove those fuses.
Jim - thanks! His drivers side passive belt motor isn't functioning - I suspect that's part of the problem. We'll do a bit more tracing tonight or tomorrow - perhaps replace the passive belts with regular ones over the weekend. As for the radio circut - I believe the interior lights are on it as well - so that's another possibility (stuck switch) - looks like we've got a bit of investigation to do -

Thanks all

Steve
 

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Good luck Steve... I have been pondering this, but the info you have is already what you need to get started and I'd need to get under there with you:)
 

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Discussion Starter · #8 ·
scubasaab said:
Good luck Steve... I have been pondering this, but the info you have is already what you need to get started and I'd need to get under there with you:)
Thanks - it's funny - I love solving mechanical problems but despise electrical issues - never really gave a big enough hoot to figure out why ...:roll: but it would appear that this time I'll just need to knuckle under and start digging!
 

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Steve,

If there is an aftermarket radio/stereo unit in there, I'd start looking there--someone went mucking around under the dash to do the install on the new one--we have all seen the product of slap-dash installations. Maybe the electrical tape came off a poorly done splice.

If you are going to convert away from passive belts, I have two sets out of 3 door hatches that are/will be just gathering dust (some are out, some not). Side panels for the back as well--postage to your environs for just the belts might not be too bad--side panels might be something else due to the size.

Good luck.
 

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SteveTheFolkie said:
...just need to knuckle under and start digging!
No knucking or digging required, just thinking.
Here's how you do it:
1) Measure both power and ground (that means knowing what voltage you should see and where you should see it).
2) Isolate the circuit that fails to provide one or the other.
3) Cut the circuit in half (test it midway, or at an easy access point, so you know which end is causing the problem).
4) Repeat step 3 until you've found the problem.
 

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Thanks for the methodology. Quite logical after just a bit of reflection.....
 

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Discussion Starter · #12 ·
Jim Mesthene said:
No knucking or digging required, just thinking.
Here's how you do it:
1) Measure both power and ground (that means knowing what voltage you should see and where you should see it).
2) Isolate the circuit that fails to provide one or the other.
3) Cut the circuit in half (test it midway, or at an easy access point, so you know which end is causing the problem).
4) Repeat step 3 until you've found the problem.
Thanks Jim - I believe the fault is behind the dash - hence the "digging" reference ....:cheesy:
 

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have you found it yet? the problem in mine was the alternator bushings. New alternator but destroyed bushings (mechanic must have been severly mentally deprived). I found it odd also, but it works like a charm now! ; )
-Alex
 

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SteveTheFolkie said:
- I believe the fault is behind the dash - hence the "digging" reference ...
Unless it's an aftermarket alarm or stereo problem, that would be very unusual.
 

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Discussion Starter · #15 ·
Jim Mesthene said:
Unless it's an aftermarket alarm or stereo problem, that would be very unusual.
There is - installed by my son (who's chasing a degree in electrical or computer engineering - which is why I figure that's where the problem is ..;) ..)

Haven't had a chance to look into it this week - will be trying to isolate the fault on Saturday.

Thanks for the help and advice - I'll let ya know what we find.

Steve
 

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SteveTheFolkie said:
There is - installed by my son (who's chasing a degree in electrical or computer engineering ..;) ..)Steve
Maybe he could use this as credit towards his studies ;)
 

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Discussion Starter · #17 ·
silversaab96 said:
Maybe he could use this as credit towards his studies ;)
.. you'd think so ... but how many practical applications really get taught or recognized in a univesity setting? Thinking back to my experience (in the dark ages, fire had been invented, but dirt was still conceptual) "real world" problems were not all that common. I'm still trying to figure out why it was important for me to be able to determine the position of a subatomic partical within a hydrogen atom at a fixed but theoretical moment in time ....:roll:
 

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Discussion Starter · #18 ·
Well, some joy on the radio circut - no fuse - no radio - .08 volts coming from the rear speaker wires (both on the left side, just the "+" on the right side, none from the front speakers) - so we disconnected the rear speakers - but I attribute this very low voltage to residual power held in the magnets and coils -

Then we looked at the passive restraint system (thanks Jim) - we pulled the big, hairy plug attached to the "passive seat belt" control box under the relays / fuses burried beneath the rear seat and our drain went away. Apparently, as the one motor wouldn't retract the mouse (it was never getting a signal) there was constant voltage to the motor (or at least to the relay) - somewhere in the control box or one of the relays there was an issue - as the motor was getting 3.5V - constantly - door open or shut - so that over time the battery would draw down (generally over the course of a couple days).

For the time being we've popped the little "emergency hooks" into the mouse tracks so JR can fasten his seatbelts - we'll be pulling a set of standard belts from our local guy - unless one of ya'all sends me a PM - I'd rather a forum member get a couple bucks than a u-pullit operator!

Thanks for the hints and tips gents!

Steve
 

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Save yourself some time and frustration. Build a switch into your battery power line. When your son shuts off his car, he can simply throw the switch. Battery can't drain when it isn't connected.
 
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