Anyone hard wired a mv50?

If so, how did you wire in a pressure switch and dash switch?

 

Years ago I was all set to but I ended up leaving it "portable" for other reasons (numerous). I did install a pressure switch, check valve and did extensive modifications to boost performance.
I went so far as to fab a rear bumper capable of holding around 3.5 gallons of air instead of a conventional tank.

To answer your question the wiring is simple. Off the shelf they already have a 30A relay controlled by the "on/off" switch. A dash switch and pressure switch can be placed in series with, or in place of the factory switch. This is a "control" circuit so minimal wire size is all that's needed, 16g-18g (fused) is more than enough.

There are a bunch of issues with these compressors from power wire size, wiring quality (or complete lack thereof), motor quality/initial build and so on.
Many of these I have addressed here. That being said I have a CO2 set up but still find myself using this thing more often than not. Still going strong after all these years.

 

The part that confused me was that the switch is connected to the negative cable. Which seems odd to me. I was going to just leave the internals and leave the switch "on" then run the two cables coming out to a relay and then connect that to the switch and pressure switch.

 

Or should I remove everything inside except the two power wires and the. Run that to my new relay and stuff?

Therefore removing the stock switch and relay...and re wiring it like the second diagram I posted

 

I think you are over thinking it. Both diagrams are essentially the same (minus the pressure switch) and the exact spot the switch power is picked up/grounded. In the left diagram the switch ground is just tied into the power ground (bat neg cable) because it's there.
I would not bother to pick up the switch power from "ignition" or anywhere else unless you already have a convenient fuse block or something. Find the wire from the switch to the relay in the compressor, put your small fuse, dash and pressure switch in series with it (fuse first), extending the wires as necessary. That's it, no need for an additional relay or any other modification to the existing wiring other than fusing (or circuit breaker) the positive power wire. Unless you want to upgrade the size.

 

I just wasn't sure it would work since one diagram is 12v pos and the other (mv50) uses negative. So I can just extend the two switch wires. Splice in a pressure switch from the relay and attach it to an arb style switch?

 

Ok so here's a crappy diagram for wiring my compressor, and th locker, look good??

 

Looks good but, add a small fuse to protect the smaller gauge branch circuit wiring at the yellow arrow below. Do this as close to the tap, splice, or 12v source you use for control.



Semi related.
At one point I had thought of going with a permanent tank/regulator/distribution system to use with the portable compressor. I made up this manifold from solid aluminum round stock but never installed it.

 

Ok that line is only a few inches inside the compressor. Only reason I'm mounting it is because I'm using it for my locker. I'm using a viair 6 hole manifold