Replaced Cole Hersey Relay
Ok, I just finished replacing the isolation relay.
A couple of observations.
Absolutely should disconnect both batteries before attempting this. The procedure in the MB owners manual is to be followed to disconnect chassis battery.
For the coach battery, disconnect ground, then positive.
Now safe to work on the relay.
From inside, remove the nuts on each side of the isolator relay. Disconnect red and white control wires.
Unscrew the screw on the control board marked " coach battery" This screw connects to one of the the mounting arms for the relay.
Disconnect the battery connections from the rear of the isolator panel.
Loosen the nuts that hold the battery studs to the rear of the isolator panel. Back them both off about an inch.
Remove 4 screws that hold the isolator panel in place.
Pull the isolator panel out far enough to get at the mounting nuts for the relay. Remove the nuts. There should now be enough play in the relay and the mounting arms to remove it.
Install the new relay. first LOOSELY attach the mounting arms. Next position the battery studs and snug them up. Note that there is a nylon bushing between the mounting arm and the isolator panel. be sure this is fit squarely in the hole. (Also make sure there is a nylon washer under the nut that secures the stud. If you didn't remove the battery studs, but simply loosend them, then the washer and bushing should still be there!)
This isolates the battery connection from the isolator panel which is grounded. Get this wrong and it will ruin your day.
I checked everything with an ohm-meter to ground to be sure the battery studs were reinstalled correctly.
You can now tighten the nuts holding the mounting arms to the relay.
Still working from beneath the coach replace the nuts that hold the relay in place.
Now re install the isolator panel using the four screws.
Reattach the battery cables to the rear of the isolator panel. Use two wrenches to be sure to get a tight battery connection while not over-tightening the mounting stud which could ruin the nylon part)
Inside the coach, reconnect the red and white control wires to the isolator relay.
Replace the screw on the control board for the "coach battery"
At this point I retested all of the battery connections with the ohm-meter to be sure they were still isolated from ground. Cant be too careful here.
Reconnect the coach battery positive cable, then the coach battery negative cable.
Finally, with the key in the ignition and in position 0 (per the manual) reconnect the chassis power cable near the gas pedal.
This took me about two hours but I had a couple of false starts before I got the sequence right. It should only take about 45 minutes.
this is a pretty simple repair but it will test your manual dexterity!
2011 Solera 235S