Mark IVa mystery jack

[topcat0399]

Hello everyone. New poster here - owned a 1991 Mark IVa for a dozen years now. Must say I LOVE this amp.

Anyway; I Have a Mark IVa, I have the owners manual from Mesa - they dont match of course!

Jack layout/tube layout/etc dont match the pictures!

2 questions:

Is there a manual for a Mark IVa specifically (one that actually matches my amp)?

What EXACTLY is the mystery jack on the bottom of the chassis next to the transformer? Is it an EQ (remote) on off switch?

Enquiring minds NEED to know!

Thanks in advance.

 

[MrMarkIII]

I think it's Reverb on/off.

 

[stephen sawall]

In a stereo rig using a Mesa a MESA BOOGIE SIMUL SATELLITE 85 WATT CLASS A AMPLIFIER http://www.bazaar-world.com/guitar-amp-9934-MESA-BOOGIE-SIMUL-SATELLITE-85-WATT-CLASS-A-AMPLIFIER it turns the EQ on and off on the satellite at the same time as the IVa.

 

[Boogiebabies]

In a stereo rig using a Mesa a MESA BOOGIE SIMUL SATELLITE 85 WATT CLASS A AMPLIFIER http://www.bazaar-world.com/guitar-amp-9934-MESA-BOOGIE-SIMUL-SATELLITE-85-WATT-CLASS-A-AMPLIFIER it turns the EQ on and off on the satellite at the same time as the IVa.

It does sound like the EQ remote jack.