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Discussion Starter · #1 ·
I am having trouble diagnosing a 'Rear Light Failure' in my 2000 9-3. Fuse #29 (10A) blows within a minute of being replaced, but only if the car is in motion. The fuse stays intact for hours if the lights are running off the battery or if the engine is running.

All bulbs on that circuit are of the proper specification and there are no apparent shorts or grounding issues (all connectors and sockets read ~11.6V when run off the battery and ~13.8V off the engine). The grounding nuts are also securely fastened under the fuse panel. I have noticed that the plastic housing immediately around the right license plate bulb socket (inside of the assembly) and the plastic housing immediately around the right tail-light show signs of melted plastic.

I have tried driving around with each of the light sockets unplugged from the harness hoping to isolate the problem, but have had no luck. Again, the problem only occurs when driving; I can leave the car parked for HOURS with either the battery (~11.6V) or engine (~13.8V) supplying power and have no issues. Is there anything mechanical (brakes, steering, etc.) that could cause issues with this part of the wiring harness?

These are the lights that I have checked:
-Rear-right tail-light
-License plate lights
-Front-right parking light

Thanks in advance!
 

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I suspect that someone has forced the wrong bulb into the license plate lamp socket.
Today, with minimal quality and plastic replacing glass, it is a must to use the correct bulb in the car or the house.

Reform is needed here as well.There must be international standards and truth used in presenting the bulbs/lamps to the public.

Too many lumens or candlepower will melt the plastic, resulting in damage which can draw excessive current which, in turn, will burn out a fuse or the harness.

The '96 uses a C 5W plate "festoon" bulb.., but the 9-3 model may use something else.
And all this over a silly license plate light:cheesy:...not worth it...
 

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Discussion Starter · #3 ·
Thanks for the reply earthworm. I am absolutely certain that all lamps match Saab's specs. And I certainly agree with you on the need for international electrical standards with the flood of new lighting technologies that are surfacing.

As mentioned in my first post, the fuse only blows, and subsequently, the rear light failure warning only comes on when the car is in motion, which leads me to believe that something in the suspension or the steering column is causing the problem.

I have never been able to recreate the failure when the car is NOT moving (revving engine, changing gear selector (auto), any combination of other accessories running/not running, etc).
 

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HTML:
 I have noticed that the plastic housing immediately around the right license plate bulb socket (inside of the assembly) and the plastic housing immediately around the right tail-light show signs of melted plastic.
How did this happen?
To save time, prevent the entire inspection of the harnesses, isolate the cause, which seems to have been done. You have some 50 fuses to work with, one or two may pertain.
 

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Well, the one thing that you do when driving that's different than not moving, is that you are using your brake pedal. Try turning on the flashers and see what happens... Ron
 

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Rob - My theory after looking at the WIS diagram is that something is bouncing around as you are moving. It looks like connector H4-3 goes to the license plate and connector H10-19 goes to the front right lights. Try disconnecting H4-3 and driving around. Good luck it seems like you're on the right path already. Two other items on the schematic are the TWICE unit and connector 258 (trailer lighting connector) Jeff
 

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Is the car automatic by any chance? It could be a short with the reverse lights (front or rear). Once you move the shifter from P to D you would short the fuse.
 

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Fuse 29 blowing

Rob I know you had this problem some time ago I just wondered if you ever got to the bottom of the problem as for the last 2 months I've had the same problem. With the fuse blowing when driving also noticed the melted plastic I've even tried led bulbs. I've recently removed both number plate bulbs yet the fuse still blows. I've even paid a saab dealer (servicing) who could not find any fault.
Still the problem continues.
Car is 9-3 2000 same as yours.
 

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Rob I know you had this problem some time ago I just wondered if you ever got to the bottom of the problem as for the last 2 months I've had the same problem. With the fuse blowing when driving also noticed the melted plastic I've even tried led bulbs. I've recently removed both number plate bulbs yet the fuse still blows. I've even paid a saab dealer (servicing) who could not find any fault.
Still the problem continues.
Car is 9-3 2000 same as yours.
Where exactly is it melting? That's your clue. Is the wire getting too hot, or one of the lamps getting too hot? Something somewhere is getting you too much current. It could be a really bad bulb, or a wiring or lamp socket issue.
 

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The numbers plate illumination is NOT a high quality area...I think it is overly fragile..I'd remover the entire assembly and inspect it on a nice work-bench with good lighting...even a magnifying lite..
Perhaps something is too loose...or broken..
Imagine the dealer cost here....$200 for lousy license plate lites...
 

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Where exactly is it melting? That's your clue. Is the wire getting too hot, or one of the lamps getting too hot? Something somewhere is getting you too much current. It could be a really bad bulb, or a wiring or lamp socket issue.
It's the housing immediately around the socket black plastic clearly getting too hot. There are 2 bulbs I took left one out seemed ok swapped over removing right one again seemed ok fuse intact. Put both back in fuse blows tends to be when accelerating but that's not always the case. So logical assumption two bulbs drawing too much current. So I thought I'd try an LED equivalent right hand one worked ok but the left one actually started to smoke and of course no longer works. So decided just to live with 1 x bulb this worked for a week or so then the fuse started to blow again. Hence the removal of both bulbs, could not believe it when the fuse went yet again. I'm very suspicious of the evidence of over heating, but that might be a red herring. I think earthworm's idea makes good sense sounds like there could be an intermittent short circuit behind the socket. I suppose there is a chance the problem could be elsewhere on the circuit even the front parking lights as they are on the same circuit. The car has had some major work due to the engine bulk head failing again saab dealer cost a lot this was a design fault many cars recalled. I think I'll continue to focus on the rear of the car for now.
 

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It's the housing immediately around the socket black plastic clearly getting too hot. There are 2 bulbs I took left one out seemed ok swapped over removing right one again seemed ok fuse intact. Put both back in fuse blows tends to be when accelerating but that's not always the case. So logical assumption two bulbs drawing too much current. So I thought I'd try an LED equivalent right hand one worked ok but the left one actually started to smoke and of course no longer works. So decided just to live with 1 x bulb this worked for a week or so then the fuse started to blow again. Hence the removal of both bulbs, could not believe it when the fuse went yet again. I'm very suspicious of the evidence of over heating, but that might be a red herring. I think earthworm's idea makes good sense sounds like there could be an intermittent short circuit behind the socket. I suppose there is a chance the problem could be elsewhere on the circuit even the front parking lights as they are on the same circuit. The car has had some major work due to the engine bulk head failing again saab dealer cost a lot this was a design fault many cars recalled. I think I'll continue to focus on the rear of the car for now.
No, I don't think it's logical that the bulbs are drawing too much current. Even if they were, replacement with stock bulbs would fix that. No need for LEDs.

I would look very carefully at the lamp holder and socket. If the bulbs aren't blowing, then I would figure that the short is very close to where you see the melting. Maybe some metal got crammed down into the sockets.
 

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Disconnect the connector serving the number plate plate yesterday.

Did a couple of miles drive no problem, however today fuse blew within a few 100 yards. So I can discount the number plates. Next I'll disconnect the RH side lights if no problem then I'll know the problem must be the front lights, hopefully I'll get to the root cause by deduction!
 

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Disconnect the connector serving the number plate plate yesterday.

Did a couple of miles drive no problem, however today fuse blew within a few 100 yards. So I can discount the number plates. Next I'll disconnect the RH side lights if no problem then I'll know the problem must be the front lights, hopefully I'll get to the root cause by deduction!
What does "disconnect" mean?

If the problem is in the wiring, disconnecting it from the bulbs won't prove that the wiring is okay (or not okay). You have only proven that it isn't the bulbs or the bulb holders for the licence plate lights. The wire to the licence plate lights could still have an issue.
 

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Fuse # 29 keeps blowing

I chased the same problem around for a month on my 98 900S, changed all the bulbs, tore the back all apart, checked the wiring to the tailgate, etc... and finally I ventured up front found the problem in the front wiring harness. At an instant when fuse #29 was not blowing, I started pulling on the front wiring harness that comes from the right front parking light and the fuse blew and a small puff of smoke came from a section of the wiring harness near where it is snap tied to the strut brace. After disecting the harness I found a bare section of the green/white wire that came from the parking light. When my engine would torque under acceleration, the wire would short out. I repaired the wire and have had no problem since.
 

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This is a fantastic first post for you. And, welcome to the forum. ;ol;

It brings to light the problem of wire chafing and provides a great starting point for troubleshooting, i.e., where the light wiring makes contact with the chassis and any sharp edges.
 
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