At 03:49 PM 6/9/2012, neil n wrote:
>Seems to me I should see continuity.

Continuity is a slippery word when it's printed on the front of a
meter (and when it's not) so I tend not to use it.

As a general rule (and it's because I can't remember whether there
are any exceptions that I'm waiting on Mr. Bentley) all things
labeled ground should in effect be connected to the negative battery
terminal.  Whether it's ok for there to be half an ohm or whether the
maximum is 0.002 ohms, or whether the actual measurement point that's
important under the circumstances is pin X on the ECU rather than the
negative battery post are matters for individual consideration.

Continuity beepers on DVMs may beep at 150 ohm, or 50.  For Van
purposes neither one would be even remotely considered a good
connection.  A test light is better since it puts some load on the
connection.  But the only way to measure quality of these connections
beyond the test-light level is to measure millivolts directly across
the connection or set of connections under consideration while
they're operating under load.  By this you can discover the
*functional* quality of the connection under working conditions,
using commonly available tools.  Because functionally the job is to
get as close to 100% of the supply voltage to the load as possible,
losing only some acceptable minimum in the supply and return
paths.  The emphasis is slightly different with senders but the
methods are the same.

So a major question with grounds is, what's the voltage between one
ground and another (alternator case to engine, say) when things are
operating; and is that an acceptable difference.

Now all that being said, and with the caveat of "not quite always" =
yes, your meter should certainly show continuity.  Using a test light
from +12 to the ground in question will tell you more (though not
enough) about quality by how bright the light is; but I wouldn't use
a test light around the ECU just in case some sender return is very
delicate (not to mention hitting the wrong pin).

Yrs,
d