re: "...You attach one lead of the side marker to the tail light lead and the other to the signal lead. [Right side] works as advertised. I hooked up the left side the same way as the right however after five blown fuses I gave up and put it back as before. Right side still flashes. The fuses that blew were the signal fuse, right tail light and lrft tail light. Why the difference?..."


Aaah, okay, let me try again -- I'm just trying to help.

Let's say, for instance, that your side markers have two wire leads, ostensibly for the conventional + and - leads to power the bulb.
Let's also say that your left light....
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Sidebar: I'm assuming it's the rear, rectangular, red, side-marker just ahead of the taillights that's found only on the wagon -- the sedans have side markers built into the taillight housing and no separate lamp. See my bottom paragraph, too, about the two wires.
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... works normally, correctly, when you apply +12 volts from the parking light circuit to one of the wires and the other wire leads to the common ground.
But now, you've discovered that when you connect the lead (which had gone to ground) and connect it to the turn signal circuit, it blows the turn signal fuse!
Is this correct?

Assuming it is, I'll continue. I'm suggesting that a possible problem is that there is a short in which the socket is somehow grounding on the side of the socket's circuit that is continuous with the wire that was originally grounded. You see, if the grounding is occuring on that side of the "bulb's" circuit opposite the +12v input, you would normally never see any effect of this because it doesn't matter whether the circuit grounds at the socket or through the OEM grounding wire -- in either case, the bulb lights up and doesn't blow any fuse because the current still passes through the bulb before grounding.

But now(!), you've disconnect the original ground wire and are connecting that wire to the +12v turn signal circuit. So, while the parking lights still light up the lamp (because the current goes from parking light through the bulb before grounding), when you use your left turn signal, the current passes to that ground point first (which is ahead of the bulb) before reaching the bulb -- it just blows the turn signal's fuse.

Trouble is, I can't explain why the right and left taillight fuses also blow -- they shouldn't. Damn!

Does this make sense to you?

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Another sidebar: I thought I recalled that that that rear side marker lamp had only one wire (from parking light power, carrying +12v), and was grounded by it's mount to the fender panel -- so you wouldn't have a second wire to lead to the turn signals. Is my recollection wrong, or are you referring to some other side marker lamp that you may have installed yourself? Or, you haven't, by any chance, installed "side blinker" front fender turn signals (designed for the hole in the front fender that's normally found in '86-on cars under the Volvo nameplate). These do have two wires -- I've installed them in my own two '93s. But then, why would you attach them to the rear taillights' circuits, instead of the front parking lights' circuits?
Can you clarify what side-marker lights you're messing with? :-)

Thanks.