So I've been helping a friend install his 3P management, and he bought a second compressor but didn't buy a second compressor harness. Now I figured that it was simple enough to make our own harness. So we wired it to a relay like this:

85->Ground
86-> Second Compressor plug on 3p/3h harness
87-> Compressor
30-> Battery
Also grounded the black wire on the compressor.


He re calibrated the 3p system but the second compressor still does not turn on with the first one. Anybody got any ideas?