2011 Sprinter 3500: 12-relay strip under driver's seat

[ptourin]

i removed the driver's seat from my Sprinter to check out the wiring underneath. I found the X145 terminal strip with a wire from the D+ terminal to the isolator, which is what I was mainly looking for. But I also found a 12-position relay strip with positions 1, 2 and 7 filled with relays. Some of the remaining positions don't have relay bases, and I'd like to use one position to mount a relay of my own. Does anybody know where to get the bases that fit that relay strip, and what relays they'll accept?

This is a simple mod: I want to bring 2 wires up to the relay from my battery monitor, so that the monitor will open and close the relay. The relay contacts will control my isolator, opening it when my batteries are charged so that the alternator will no longer charge them.