It appears to me that the diode string is what makes it a distortion circuit.
With the string removed you should have a clean signal.
If you do not, then you have other issues that need to be addressed first.

The output topology is Class A/B.
So with no current reading across the emitter resistors, the amp is in Class B.
Fellow member Enzo has an excellant old school method of setting the bias.
-Measure the current draw from the mains while turning the bias trim pot.
When you start to see more current being drawn, the amp is now entering the Class A part of A/B.
Turn the trim pot back down a tad and you are done.-
There is not a 'specific' current draw across the emitters that can be stated.

There are many different schematics on this amp model.
here is the '1982'.
See if it is close.
You need to troubleshoot the circuit.

Here is a pic of the jack and the Harvard wiring.
The numbering scheme that you used depends on how you are looking at it.
Use the jack drawing and you will get it right.

Nice work!

Not too sure what you want to do.
The input sensitivity of the module is listed as 80mv's.
If your input signal is too hot, knock it down with a voltage divider.
2 resistors. 1 in series. 1 to ground.

Well how about a schematic?

"Yep. Tried that and even with the input to the power amp shorted it keeps making noise."
So it's in the power amp.
Or the power supply.
Have you monitored the power supplies when the issue occurs?

Have you tried inserting a signal in to the Power Amp In jack?
By doing this you isolate the preamp from the power amp circuit.

If you look real close there should be numbers on the rear of the plug.

Conflicting info on this one.
On the left is a rate & depth control for Tremolo.
Assuming the 400-210 is the same as the schematic posted, then Pin #1 of the ft sw socket will turn on & off both the Distortion & Fuzz circuits.
No either or. Simply both.

Can you post a picture?

Here is a pic of the Musician 400.
Does yours look like this?
Rate & Depth are the Tremolo controls.

Not too sure what amp you have.
The Musician 400 schematic that I have shows it having Tremolo.
The schematic does not show a footswitch activation for Distortion, just Fuzz. (Pin #1)
The manual states that pulling Pin #1 low (activate Fuzz) turns on Distortion/ Fuzz.
You might want to call Peavey and ask for the correct schematic.

I don't think that you have it right as of yet.
The output is cathode biased not fixed as in the Fender.
Why not hook it up as I stated in my last post.