Wiring tank heater for motorhome question

[Shawn]

My motorhome is 2019 model of Chateau, black and gray tank doesn’t come with the tank heater. But the have B/G tank heater switch preserved.
I am planning install the heat pads onto black and gray tank, and the pads install was very easy. My question is for wiring, I saw the power control box 12 V section marked #7 fuse for tank heater, the color for the wire is green, then I find green wire behind the power control box and connected onto a relay. Not sure why? The heating pad only require 5 Amps for each, why need relay? And how can I connecting these wires for the heat pads?
Anyone has the diagram for the 2019 model chateau? Also how can I run the wires through behind the cabinet?

Thank you for the helps

[gte534j]

There is a thermostat installed in the heater pads to not turn on until its cold. Its around 40F or so. Are you testing out the pads below that temp? A infrared thermometer is really helpful to see if they are working.
You can just wire more pads in parallel on the existing pad wires. I also would recommend adding elbow heater pads for the lines.

[Shawn]

Thank you for the message, Yes these pads are auto on with the build in thermostat, but I still want add the on/off switch onto the pads, since you don't want the pads heat up the empty tank when the temp below 40F. also, the pads and thermostat will using a bit of power from battery, so, I like to add the on/off switch to them, only turn them on during the cold weather.
I really like to use the Thor factory preserved Tank heater opening on the control panel, and fuse pre wired on the power control box, but no diagram to be found, also, look like the tank heater prewired to a relay???

[THorRVForLife]

Did you ever get this figured out? I'm trying to do the same thing: add tank heaters, and I'm trying to see if I can use any of the wiring that's already in there. I think the two relays are not for the tank heaters... Like you, I've got a green wire coming off the fuse labelled "tank heater", but I can't really figure out where it goes, and/or if there's any connection to the control panel, which has spaces (but not actual switches) for great and black tank heaters.
Thanks!

[bry899]

adding tank heating pads.

I have a 2018 Four Winds 22E, and no heating pads, but the control panel shows it was an option. (see pic)
If this is the case on your control panel then most likely your coach is prewired for the pads.
Remove the panel and pull out the wiring harness. their should be 2 pairs or 4 wires not plugged into the control panel:
the 2 green wires are live 12v power, the black goes to the black tank (you need to add a switch for 1 green and the black wires), the gray wire with white stripe goes to the gray tank. (and you need another switch for 1 green wire and gray wire)
Underneath the coach each holding tank along with their respective tank level wires you will find the wires needed for the pads.

[Mikmal]

That takes care of the tanks. How are you heating the lines to prevent them from freezing?

[bry899]

Originally Posted by Mikmal

That takes care of the tanks. How are you heating the lines to prevent them from freezing?

Keeping the water lines from freezing would be a separate topic from wiring tank heaters.
anyway,
We have camped and boondocked a few times where the temperature was below freezing overnight, and warmed up to 40's and 50's during the day.
With the heat on we never had any pipes freeze, we would disconnect the water hose outside and any water that was in the the hose did freeze.