Hey guys.

quick question.

I've got 2 cabinets;

my Marshall MA412 - One input, 16 ohms.

A randall 4x12 cabinet, with a 16 ohm and 8 ohm input.

My head outputs 1x 16 ohms, 2x8 ohms and 2x4 ohms.

Could i go;

8 ohm out -> 8 ohm randall cab in
8 ohm out -> 16 ohm marshall cab in

how do I wire this as a full stack?

Now this is all stuff you'll find in your amp's user manual, so you can consult that for questions of this nature, too. Here goes:

4 Ohm
8 Ohm
16 Ohm

You only ever use one of these taps at a time.
The 8 and 4 Ohm taps have two jacks each, with the jacks being wired in parallel.
This means that for the 8 Ohm tap, you can either hook up one cab rated at 8 Ohms, or two cabs rated at 16 Ohms each, since two 16 Ohm loads in parallel equals one 8 Ohm load. Likewise, when using the 4 Ohm tap, you either plug in one cab rated at 4 Ohms or two cabs rated at 8 Ohms each.

Set your Randall to 16 Ohms. You now have two 16 Ohm cabs. Plug them into the 8 Ohm jacks. As stated above, they equal a load of 8 Ohms together.

While the amp likely will be okay if you use two differently rated cabs (long as you're running them off the same tap), you will notice a difference in volume between them, so don't do that.
Quote by TheQuailman
Now this is all stuff you'll find in your amp's user manual, so you can consult that for questions of this nature, too. Here goes:

4 Ohm
8 Ohm
16 Ohm

You only ever use one of these taps at a time.
The 8 and 4 Ohm taps have two jacks each, with the jacks being wired in parallel.
This means that for the 8 Ohm tap, you can either hook up one cab rated at 8 Ohms, or two cabs rated at 16 Ohms each, since two 16 Ohm loads in parallel equals one 8 Ohm load. Likewise, when using the 4 Ohm tap, you either plug in one cab rated at 4 Ohms or two cabs rated at 8 Ohms each.

Set your Randall to 16 Ohms. You now have two 16 Ohm cabs. Plug them into the 8 Ohm jacks. As stated above, they equal a load of 8 Ohms together.

While the amp likely will be okay if you use two differently rated cabs (long as you're running them off the same tap), you will notice a difference in volume between them, so don't do that.

So, from the 8 ohm jack to the 16 ohm cabinet, twice?