93 854 Brake light fuse blowing

Post by **JimBee** » 04 Dec 2016, 10:46

One more little glitch in otherwise good runner.
Looking for the easy solution, I suspect the bulbs are wrong wattage. The following guide on MVS indicates 21 watts.

https://s3.amazonaws.com/images.matthewsvolvosite.com/bulbs-composite.jpg

But is that correct for the 93 sedan? I don't think I have a short circuit b/c the fuse lasts a while, suggesting hi over-amp draw. That fuse is only 10 amps, so it's pretty sensitive to loading. One poster said he cured his problem by upping the fuse to 30 amps and he "wasn't smelling any smoke yet". I'd rather not do that.

The switch is a possibility I suppose. If the bulbs installed are correct I'll look at that.
Suggestions welcomed.

Post by **abscate** » 04 Dec 2016, 10:52

The fuse can take several seconds to blow. If it lasts for minutes (with brakes on of course) then I would agree that there is a high draw somewhere rather than a short. A Short can be intermittent though - so time isn't always a good marker.

Download your 1993 user manual and look up the bulb type in the chart to get primary data on the right parts.

Post by **JimBee** » 04 Dec 2016, 15:13

Solved? Too soon to tell. But I found a couple of likely culprits that might be combining to blow the fuses. The drivers side taillight socket board has some corrosion near the harness plug. Might that increase resistance, although the sockets themselves look okay.

Plus, most of the bulbs are the 1156 which are the ones commonly sold in the local parts stores and are higher wattag than the 21 watt 7506 that's recommended in the MVS post and the 93 850 owners manual. NAPA has some Wagner crossovers for the 7506 that are made in China. They are supposed to be 21 watt, but I might buy a couple from Volvo.

Fortunately, I had a complete set of 93 tail lights in inventory, so I've swapped in that clean socket board and have 1 7506 in each side (I just had 2). I stood on the brake for about a minute and so far all is good. We'll see.

?

Post by **JimBee** » 04 Dec 2016, 20:27

Unfortunately, those tweaks didn't solve it.

I have a list of tests and everything lined up to do them, but I'm wondering now if in fact pressing the brake pedal is what is blowing the fuse. I have not actually seen that happening, I just know that it happens after driving around a little, stopping and starting.

One concern I have is there is a spade connector sticking out of the brake light fuse socket. It's kind of floppy and there's no wire connected to it. I'm wondering if that connector—basically a piece of metal—flopping in the socket—might be shorting the circuit. I'll put in a new fuse and wiggle the spade to see if it affects the fuse. I've seen them on other 850's at the junk yard so I guess it's a common hack for something.

Does anybody know how to get those out without damaging the socket? That might be a good place to begin hunting for the problem on that circuit.