Would you be so kind as to post the link?

That symbol is trying to indicate that the wiper (the middle leg) gets attached to either the left or the right leg.

The + of the bridge rectifier is marked 'A'.
The - is marked 'D'.

I don't believe that switch is available anymore.

Have you attempted to contact Fender?

Use the FX jacks to help narrow it down.

The Send to another amp is your preamp.

The Return is pretty much a line into the power amp.
You can use the Send from another amp or any instrument.

How are you setup test equipment wise?

There are signal voltage references on the schematic that may help narrow down where the issue lies.

The IC U2B is set up as a self running low frequency oscillator.

Look above it at IC U3B, pin #9/ R20 also has the Lambda symbol.
I take it that R20 is the LDR.

U2B's oscillating output will allow a change in the resistance of R20.
There is your Tremelo.

If the are all 8 ohms, then the equation works out to 5.33 ohms.

For those following along:

Schematic??

Here is a link of a post from 2009.
And the pics are still there!
(F U PhotoBucket)
https://www.ultimate-guitar.com/forum/showthread.php?t=1172707

I believe that you are missing the point of the Earth connection.

"Wall Wart" power supplies are typically rated as 'Double Insulated'.

Therefore there is no need for a connection to Earth Ground.

If you are having noise issues with the amplifier, I would look into why.

The power pack itself may be the issue, noise wise.

"so how do I determine which of the pins is which/is ground?"

Use your ohmmeter.
The ft sw ground pin will be at the same potential as the chassis.

The function pins will not.

Pull any function pin to ground & it will 'operate'.

Yeah, I really did not study the circuit for too long.

I do believe the OP is asking too much from a Forum.