Where is the ground wire?

There's a bolt back by the pcv valve that should have a braided wire coming off of it to the firewall. It's about 4 inches long.

The extra 4 gauge ground connects to the block where the battery ground bolts to, or to
the A/C mounting bracket. It connects to the chassis at the place the battery pigtail ground bolts to.

Avoid using the timing cover or water pump bolts since they corrode and will make a poor connection.

From my post on grounds, which isn't exactly rocket science...

The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects.
The 3G has a 130 amp capacity, so you wire the power side
with 4 gauge wire. It stands to reason that the ground side
handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery & alternator

Picture courtesy timewarped1972