Bob:

IIRC, the tag is a white paper (or plastic) sticker that's wrapped around the harness right behind the battery, just before the harness makes its way through the main firewall and onto the top of the motor. The tag has the part number printed on it, as well as a born-on-date!! Month, day and year are all there.
If you can't find a tag, take a look at some of the exposed wire going to the top of the thermostat (or other points off the harness). There should be a couple wires sticking out from the black plastic sheathing of the harness just enough for you to check the condition of their insulation. Mine were cracked; of course yours may or may not be, even if the harness is original. But cracked insulation would indicate an old harness. You really don't want to cut into it unless you really need to!

Brian

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Brian
1995 E320 wagon