Can anyone with experience in installing a new stereo to a 1987 Vanagon
provide a definitive answer about whether the rear speakers that year shared
a common ground?

I have 4 wires coming from the rear; they are colored as described in
Bentley 97.176. That diagram suggests to me that they do *not* share a
common ground.

I have seen one message in the archives that says they do not, and that
installation of a modern radio will go fine. There is another message that
says the ground is melded somewhere in the back and that you should not be
fooled by the presence of two wires. I've received a private email warning
the same thing.

Others have said I should use a VOM to check for myself. If I had a VOM (a
voltage ohm meter?), what should I look for? How do I use one to test these
wires? (I am sure I can borrow one from somebody).

Thanks,

Tim Beidel
South Portland, ME
1987 Syncro Westfalia