You obviously don't have a common ground. The only 'ground' you have is
from the antenna mount, via the coax shield, to your radio. When you hook
your ground post to the chassis you have extended the 'ground' and caused a
higher swr.

Try running a ground strap to a common metal point on the vehicle...if you
can find one these days. Check with ohm-meter and make sure as much of the
car as possible is connected together.

Of course you will probably have to retune the antenna now.

Dan/W4NTI

"Michael J. Donohue VE3YF" wrote in message
...
Hi:
I have suddenly developed a weird mobile setup problem. When
my IC-706 is in the car and antenna (HF) is hooked up, everything is
all is ok ie swr. But when I hook up the ground wire from the frame of
the car to the ground post I now get get high swr. I have checked the
antenna system with an analyzer and it appears ok. Any idea's???

73 De Mike
VE3YF