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Discussion Starter #1
Fuse #5 has blown twice in the last three days. This controls the tail, side marker. front clearance and license plate lights. All of them go out. Everything works when I replace the fuse, except for one license plate light (bad bulb ?). The parking light switch also works. Please help.
 

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2005 OBW 2.5L, 1989 Subaru Justy, RIP Blu
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There is a short in the harness that passes from the car to the tailgate. It is not too unusual.
 

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Discussion Starter #4
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I used a multimeter to do some sleuthing. With the ignition off, fuse #5 was drawing 11 Amps !! Started taking out one bulb connection at a time. Only had time to check tail and license lights. Left Tail light reduced current to 3.5 Amps. Removed bulb to find out the two "bumps" at the bottom had fused together ! Need a new bulb. Still need to figure out where the remaining 3.5 Amps is coming from. This might explain why I had to replace the battery a couple of months ago. At that time I had thought the battery had just gotten too old (7+ years).
 

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With the ignition off, fuse #5 was drawing 11 Amps !!
With the ignition off! That's strange, because with the switch at OFF, the tail and illumination relay should be open, and there should be no path for current to the bulbs. If you keep pulling bulbs, probably the current will fall to zero when there's no bulbs in the circuit downstream of the fuse. But why is there power at fuse #5 to begin with?

The 11 Amps current seems shocking (fuse #5 should be 10 Amps), but it isn't if we take into account that fuse #5 supplies current to at least eight bulbs; two front side marker bulbs, two license plate bulbs, two tail light bulbs, and two rear finisher (tailgate) bulbs. I don't know what bulbs are used in the 1999, but many automotive clearance and tail lights can use between 3/4 and one Amp. So there's going to be a fair amount of current in that circuit normally.

This means that if there's 12 V power going to fuse #5, there's going to be several Amps of current through it, even if there's no faulty bulbs (like the one that was found) or sockets. That being the case, it seems to me the real issue to be addressed is why there's power going to fuse #5.

Check for 12 V at fuse #5. If it's there then are you sure the Parking Light switch at the top of the steering column is Off? (If not, then turn it off and see what happens.) If the switch is Off, then try pulling the tail and illumination relay (to the right of the in-cabin fuse panel which to the left of the steering column) and see if the Voltage at fuse #5 disappears.

If it does disappear, then the relay is remaining closed. This could be due to an internal failure, or because the relay energizing coil is still being supplied 12 V from the ignition switch (not likely, but still a possibility).

If pulling the relay out doesn't change the Voltage reading at fuse #5, then there could be a short downstream of the relay to a 12 V line, or the Parking Lights switch could be defective.
 

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Discussion Starter #6
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Thanks for the tip on the parking light switch. It indeed was on and was providing power to fuse #5. With the switch off there is no current draw. So my only problem was the tail light bulb. I have attached a photo to show how the contacts melted. I have scratched a gap between the two to see if the bulb still works. It does but I'm going to get a new one anyway.
 

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Great!

As for the bulbs, get a few and replace the others of the same type ("bayonet base"), or at least check them all.

It's not uncommon for the contact surfaces on both the bulb and the socket to oxidize over time, especially if the bulb hasn't been removed/replaced. (Removing/replacing causes some scraping of the contact surfaces and therefore cleaning, which improves the electrical connection.) When oxidation occurs, the current through the contact causes it to heat up, and the material softens and collapses, just as your photo shows.

(There's a number of other threads here with similar photos -- in some cases the two contacts have come together, causing the brake light filament and the tail light filament to glow at the same time. In other cases, the contact material extends over the side to the brass color base which is ground, and this blows the fuse.)

I wouldn't be surprised if the other bulbs are also showing signs of deteriorating contacts and it might be only a matter of time before more problems are experienced for much the same reason.
 
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