From here:
http://www.dieselbenz.info/dieseling_index.htm

there is this guide:

http://www.dieselbenz.info/dieseling_door_check.htm

which may help you along.

On my '79 TD I found it under the passenger-side floor mat, under this
plastic guard thingy.  My four-way splitters don't look anything like
the ones in the manual though; mine're like tridents with the "feed"
coming down the middle of the three-side, passenger door coming out
opposite that, and two back doors (and I suppose fuel and hatch locks as
well) out the two pointing in the same direction as the feed.  Gotta try
to diagnose my own problems tomorrow.  ;)

good luck,
-tom!

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