Without modifications to the amp, you will need a battery in the footswitch to run the light.
You can modify your existing footswitch, or you can buy one already made, something like this: http://www.ebay.ca/itm/Voodooman-FootSwitch-1-Button-W-9V-DC-powered-LED-/380503784108

  Your transformer wiring looks correct.
Now you need to find out why it blows the fuse.  That is where the limiter lamp comes in.
Do not connect any speaker to the output until you determine there is no DC voltage on the output wires.
  The speaker may have been fried by a blown power amp and you don't want to ruin another speaker.
  The output devices (Q2 and Q3) should be checked for shorts, and their emitter resistors should be checked for open condition.

  This amp is ok to use with a 4 ohm load, specs are 120W@4ohm, 80W@8ohm
http://www2.randallamplifiers.com/images/stories/manuals/RG100ES-RG80ES-OwnersManual.pdf

So the fault was not caused by using a 4 ohm load.
Whether the fault is the breaker, or the breaker is just doing it's job is something you must determine, as Roly mentioned above.

Quote from: markorock37 on May 10, 2013, 01:21:20 PM
Transformer wires are correct. No voltage on P8 or P9 to ground unplugged.

We need to know the AC voltage at the wires that attach to P8 and P9.  Not DC voltage, and not at P8 or P9.
Disconnect the brown and brown/white wires from P8 and P9, connect your meter to the wires.
What is the AC voltage from brown to brown/white wire?  AC volts from brown wire to chassis ground?  AC volts from brown/white wire to chassis ground?

  There is no schematic in the attachment.

Quote from: Roly on May 09, 2013, 10:38:47 PM
Isolate the fan rectifier, D8-D11, and retest voltages, particularly P8 (TP5).

I think you mean D108-D111, also C116.

But before this, check what Enzo asked in reply #17.

 Is R61 ok?
A couple of points I'll throw in: 1)  Those 35V caps (C108 & C109) should be exploding if they're getting 50V on them, or at least bulging.
2)  The two transformer windings are common to the fan circuit, maybe something weird there?

But for quick check, disconnect P8 & P9 (brown and brown/white), what AC voltage do you measure between those wires?

  And you need to verify that it is not a speaker issue.

Quote from: Roly on April 15, 2013, 01:43:35 AMThat's what the little "[informative][useless]" buttons are for.

Thanks Roly, did not even realize those buttons existed (under posters name). 

  That sticker is specifications regarding the incoming power from your wall outlet.  It will tell you voltage, frequency, and power consumption of the amp.  So in your case the amp uses 120 watts from the wall (to deliver 50 watts to the speaker, not very efficient).

  If you need, here is a picture of series and parallel wiring of the 2  speakers.  Pay close attention to the + and - terminals of the speakers in the series arrangement.
http://www.svvintageamps.com/images/2-speaker-wiring-diagram.gif

Quote from: g1 on April 11, 2013, 11:42:03 AM

Quote from: J M Fahey on April 11, 2013, 02:40:51 AM
afaik the Vox has 16 ohms only output, or maybe 8/16 , but that pair of Frontman speakers is wired for 4 ohms.

Oops! Thanks JM, I had forgot to consider impedances.
The Fender speakers wiring will have to be changed from parallel to series (simple).  Then it will be an 8 ohm cabinet.
  The Vox has an 8/16 switch on the back which will have to be set to 8.  The Fender cab will have to be plugged into the EXTERNAL spkr. jack, not the extension jack.  This will mean the Vox's own speaker can not be used at the same time.
  When used by itself, the Fender amp will give a tiny bit less power into the 8 ohm cab than the 4 ohm stock  cab wiring.
ctguy1955, I hope this is still a workable scenario for you.

Sorry about this, it is incorrect.  To quote you from an earlier post "I should just delete that last entry as it makes me look like the jerk that I feel I am" 
JM is completely correct,  if you rewire the fender speakers in series, you will have a 16 ohm cab. (not 8 ohm as I incorrectly stated).
  Then you can set the Vox amp to the 8 ohm position and use the EXTENSION spkr. jack.  All 4 speakers will be working.
  As I mentioned earlier, when you use the Fender by itself, it will be putting out a little less power than with the stock wiring, but I doubt you will even notice the difference.

Quote from: g1 on April 10, 2013, 07:47:52 PM

Quote from: Andy54 on April 10, 2013, 03:47:36 AM
The attached pic I think shows the transformer in question. It has three red wires attached to the board.

  That is the power transformer.  It is not "stepping down" 240 to 120V, it is transforming the 240V to the voltage the power supply uses.  You plug it in to a 240V outlet, yes?  So it is already wired up for 240V operation.
  It is the same size/weight as a north american version of the amp would use, you can't downsize.  Yes, new amplifiers deliver more power and weigh less, like modern cars do. 

Sorry about that post, the picture showed the power transformer and I did not realize there was another "step down" transformer in the cabinet.
  Sounds like you are getting it sorted out, good luck.

Quote from: J M Fahey on April 11, 2013, 02:40:51 AM
afaik the Vox has 16 ohms only output, or maybe 8/16 , but that pair of Frontman speakers is wired for 4 ohms.

Oops! Thanks JM, I had forgot to consider impedances.
The Fender speakers wiring will have to be changed from parallel to series (simple).  Then it will be an 8 ohm cabinet.
  The Vox has an 8/16 switch on the back which will have to be set to 8.  The Fender cab will have to be plugged into the EXTERNAL spkr. jack, not the extension jack.  This will mean the Vox's own speaker can not be used at the same time.
  When used by itself, the Fender amp will give a tiny bit less power into the 8 ohm cab than the 4 ohm stock  cab wiring.
ctguy1955, I hope this is still a workable scenario for you.

Quote from: Andy54 on April 10, 2013, 03:47:36 AM
The attached pic I think shows the transformer in question. It has three red wires attached to the board.

  That is the power transformer.  It is not "stepping down" 240 to 120V, it is transforming the 240V to the voltage the power supply uses.  You plug it in to a 240V outlet, yes?  So it is already wired up for 240V operation.
  It is the same size/weight as a north american version of the amp would use, you can't downsize.  Yes, new amplifiers deliver more power and weigh less, like modern cars do.