Im going to go out and work on it here in a little bit. I can inject a signal into and have an oscilloscope and a dummyload. 
You want me signal tracing live?  While testng dcv+ and dvc- ?     Will look over everything suggested first.

Have a Marshall 8100 with a dead overdrive channel.  Have plugged into return loop and power amp is ok...so its in preamp.
Have tested the 12ax7. Also tried several known good tubes.

Whats next?   I have whatever gear is needed to test.

So you are mad we are not psychic mind readers with xray vision.   You want an answer to a question that has yet to be asked.
You wont know jack till you get a schematic and open it up.   A simple google search of 3 pole toggle switch wiring will give you a basic idea...but it's all a guess until you see how its made inside.

And wouldn't common sense suggest....that if you buy the right switch from fender....that a person could simply take one wire at a time and solder it to the new switch?   After de-soldering it off the old switch?      Unless it it a pin type mounted in a board. and if that is the case..there is no thinking involved.

Have a solder gun @40 watts?
Have a de-solder bulb?
Have a mutimeter?

We know you got a poopy attitude.  Leave that behind. Become humble...and learn.

Still working.  Played it several times today.  So quiet now.  The pots are just ridiculously easy to turn.  Can't say enough about that DeOxit D5.  Stuff is magic.  I'm looking for other pots to clean now!  On guitars and stuff.

you are in over your head boss.   Get a friend over to help you, you got no business putting the switch in if you don't know how it even works.

I have a compulsion to fix broken things.  Drives me nuts till I do. You guys gave me the confidence to do it.  This amp has a beautiful clear channel now. The chorus is awesome.  Never sounder better. The pots turn like butter.  That DeOxit stuff is a miracle worker. The pots where moderately hard to turn....now I could roll them all walking by with a pinky finger.

Next project...

Replacing two input jacks on another Fender Amp. An old Red Knob Twin Solid state.

I  must thank you all VERY much!!


Videos

https://www.youtube.com/watch?v=QQaBn3JVp3I&feature=youtu.be


https://www.youtube.com/watch?v=wvOdHOgAQ10&feature=youtu.be

I was pretty excited.   So it was a solder joint on the filter cap.  Only one on board that looked funny.  Like fractured around the perimeter. Could barely see it.  There was no voltage higher than .2 v   So I went ahead and re-soldered all the 4 joints on the 2 filter caps.  I cleaned the pots while I was at it and the input jacks.  Put it back together...said a prayer.  Bam.  Flipped the switch and was rewarded by the amp gods.

I got sooo lucky...cause I don't know a damn thing about electronics...lol.

Bad joint


Fixed

Pics uploading and video.

So guess what?   I FREAKING FIXED IT!!!!!   WHOOOO HOOOOO 8| <3) :dbtu: :tu: :duh xP 8| :loco <3)

So the next obvious move is to take the board off the chassis to inspect the back of it.   Looks like I have to take all the knobs off and the heat sink deal screws from under the chassis.  And slip board back and flip it over.

Chassis out.   Pics coming.

I love the Iommi Guitars!    I have a set of Iommi signature pickups from one a guy took apart and painted the whole guitar with a Sabbath theme...why he would take the black chrome pickups in it out...I do not know...he put some purple ones in it now.  I got those pickups for $50 on ebay make an offer!!   Real Gibson 4 wire Iommi's.   I'm gonna put them in my SG with coil tapping pots and have a screamer.

I have the discharge tool made.  It measures 970 Ohms resistance.   Also temporarily soldered one of those alligator clip leads to the black lead on my Multimeter.  Now I can ground it on chassis and probe one handed...right handed...lol.

Going to pull the chassis after dinner.

Am I missing anything?  I'm not plugging it in and doing any testing live till I get schooled by you guys on what to do. Just checking caps for voltage and discharging and inspection all unplugged.

Ok. Despite being mortally wounded today, I was able to hobble to radio shack.

I procured:

40 watt soldering iron with pencil tip.
Solder sucking bulb.
96/4 tin/silver solder .032 gauge
some pre made alligator clip leads.  well insulated.
Some DeOxit D5
1k 1 watt resistor for discharge tool
some  shrink wrap..may have some in garage...but motorcycle in the way of that tool box. I cant move it right now.


I'm going to tin the iron and cut one of those alligator clip leads in half and solder the resistor inline...cover the whole deal with shrink wrap.  Then I should be able to drain the caps if I find voltage.

Any flaws or ideas while I make up my discharge tool?

Then I'll pull the chassis. With pics. Might as well document everything, maybe a picture will help someone putting one of these back together or something.

Elsa checking stuff out.


Mauser and Zeus have to have a look as well.