Rich,
Good to hear that the car is running!
Not all the instruments have any particular thing in common, so
let's look at them one by one.
Ammeter:
The ammeter is all by itself. Since the car starts, we can assume that the
ammeter either has been bypased, is working fine, or has internal
problems.
With the engine off, turn on the headlights. The ammeter needle should
move to the left (-) side. If it does, it isn;t totally bad, and could be
fine. The ammeter will normally indicate zero, except whenpower is flowing
into or out of the battery. Most of the timewhen the engine is running the
battery will be fully charged and the car is running off the alternator.
Oil pressure:
I don't recall whether the 68 had a mechanical or electric oil
pressure gauge. If it is mechanical there will be a hose from the
right side of the block, near the oil filter to the body. This hose,
or the hard line to g\the gauge could be plugged, or the gauge could
be bad.
If it is electric, then see the next section.
This gauge also is separtate from the others. There is a sender on
the right side of the engine, near the oil filter. There is only onb wire
connected to it. With the key on, but the engine off, the oil pressure
gauge should indicated zero. Short the wire on the oil sender to ground
and the gauge should indicate full oil pressure. If this happens, the
gauge is probably good. The oil pressure gauges on our cars is not know
for accuracy. The best way to check the engine to see if it has good oil
pressure is to buy a mechanical gauge and screw it into the hole where the
oil pressue sinder is installed. I prefer to use a tee so I can get an
idea of what the dash gauge indicatws at different actual oil pressures.
You will probably find that the oil pressure will be 5-10 PSI at idle, and
about 50 with the engine reved up.
Fuel gauge and Temperature Gauge:
These gauges do have a common power source, so I will discuss them
together.
The temperature sender is mounted on the left side of the head, near the
thermostat housing, and below the heater hose connection. It also has only
one wire. As discussed above for the oil pressure, ground the sender wire
and the gauge should show flls scale hot. If it doesn't, there is a
problem with either the gauge, or, more likely, the voltage regulator for
the dash.
There is a small metal box mounted to the right, and above the steering
column, rightbehind the dash. This is the instrument voltage regulator.
There are two wires on it. If you have a test light, or volt meter, check
the voltage on the two wires (while being connected to the rebulator). One
should have 12 Volts on it any time the key is on. The other should pulse
on and off, going from 12 Volts to zero, about 1~2 times a second. If you
have voltage on one wire, and zero on the other, the regulator is probably
bad.
The fuel gauge works just like the temperature gauge. The wier to the fuel
sender is located under the plate on the floor of the trunk. Remove the
plate and you will find two wires. One goes to ground and one is a slip on
to a pin that is insulated from the surrounding metal. Ground this and see
if the gauge goes to full. If not, the problem is with the gauge, or the
regulator.
Give these a try and let us know what you find.
Peace,
Pat
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