Hey guys, I really want a second compressor. My question is, if I install next to the one i have now can i splice the power wires together or what? I am not sure how to do two compressors. I only have a 5 gal tank but i am about to buy a caboose whistle and i would like double time on the air. thanks. 
You will most likely have to add a relay or buy the HB dual relay.
And you will need at least 10ga wire coming from the battery.
Or you run a new, larger gauge wire to a power distribution block, run two wires from it for each compressor, then get the heavy duty adjustable pressure switch which eliminates the need to use a second port and pressure switch on your tank.
-Kris
Get the hb dual relay pressure switch, it is well worth the money, everything is labeled so it is easy to hook up. All you would need to do is run your power wire
J.Wal
^I like this the best - especially if starting from scratch. In fact that’s what I’m doing.
So PGgreen: What do you want? cheapest? easiest? best?
The cheapest way is to buy a plain 30amp relay and trigger it off the existing relay. Sort of daisy chain it. You just run an additional wire from the battery. This might not look the cleanest when done.
Easiest and pretty clean looking is the HB dual relay.
Go dual relay, looks great and MUCH easier, then running all the relays and wiring.
Here is another option… Spend $20ish from ebay and get a stinger 80a relay, run a 4ga wire, to handle the total power requirement, to the relay then a 10ga wire (for each compressor) from the relay to a 40amp fuse (inline) and then to each compressor. Obviously the fuse size will depend on your compressor needs.
power the relay from the pressure switch, which will eliminate the need for 2 relays and all of the associated wiring.
This is what I’m going to do as soon as I get some time to do it and can get some 10ga wire here and all of the connectors I need.
You could go with the dual relay setup if you wanted, too…