No 12v power to holding tank heater pads

2007 WGO Outlook, 31C

I have no power to the heat pads on my holding tanks (actually measured 0 VDC at the connection wires there at both pads under the coach.)  Power is supposed to come from slot #5 at the load center under the fridge, and that (15A) fuse is good.  Of course the wiring there at slot #5 just disappears into a loom as it heads off into oblivion.

This was a So Calif coach all its previous life, so the tank heaters may never have worked.........dunno.  A pair of nearly new Interstate golf cart batteries do a great job of powering everything else in the coach.  The switch that should turn the heaters on lights up red, but from what I have seen on one of the wiring diagrams from WGO, that is just an indicator that there is power at the switch ....... and you should turn it off if the ambient temp is 40 F or above.  The actual switch contacts apparently switch on a relay and the relay contacts provide power to the heaters (should be about 10A.)  My (old school) approach: if you are having trouble with a ckt with a relay in it, the relay should be considered "guilty until proven innocent).  :^)    Sorta surprising to me that a relay should even be req'd at all to switch 120 watts.

Has anyone else had this tank heater problem with a WGO class C?  If so, where do you think the relay is to be found?  (The tank heater switch is on the fridge wall and I  HOPE the fridge doesn't have to be removed to gain access.)

I don't know that I will ever use these holding tank heaters, but I would like to have them working.........just in case I "get caught" in an unplanned cold weather situation.  If all else fails, i could always run my own wires back there with a hefty toggle switch, fuse,  an indicator light and an ammeter to "prove" they are drawing current.

Thanks for any clues.....................  ed s

What was the temperature when you were checking things out?  I suspect they won't heat unless the outdoor temperature is below a certain level.

Most likely one of two possibilities.  Like Arch stated, most likely a thermostat that will control the on/off of the heaters (or maybe one thermostat for both), and possibly the relay, if there really  is a relay.  You may have to jump the thermostat out with a jumper wire if you cannot get it adjusted to a higher setting or if it is a fixed thermostat that is not adjustable.  If you get that far, you will have to find the relay if there is one and check to see if there is voltage coming into it (on the power contacts) and if you can see or hear it operate, then check to see if there is voltage leaving the relay and heading to the actual heater(s).

Look at your wiring diagram (link above in Winnebago and Chassis resources thread) and run it down with a meter.

Does the switch have 120 VAC on it or 12 VDC? Are the heaters 120 VAC or 12 VDC or both? On the only RV I had with tank heaters they were 12 VDC and did have a relay. The relay should be near the heater pads.

Ultra Heat Tank Heaters
http://www.annodindustries.com/shop/holding-tank-heaters

John Hilley said:

Does the switch have 120 VAC on it or 12 VDC? Are the heaters 120 VAC or 12 VDC or both? On the only RV I had with tank heaters they were 12 VDC and did have a relay. The relay should be near the heater pads.

Ultra Heat Tank Heaters
http://www.annodindustries.com/shop/holding-tank-heaters

Click to expand...

These are 12v pads, John.  Ultra Heat brand as installed by WGO.  No relay visible near the heaters.  A good sized split loom coming down  the center of the coach houses the 12v wiring for the heaters and  smaller looms just break out of that "mother" loom with 12v wires (with separate/dedicated ground wiring) to (1) the gray-tank heater (2) an elbow heater near the gray tank dump valve, and (3) a third heater pad for the black tank.  As of now, I have no reason to suspect anything is wrong with any of the heater pads themselves .........just no 12v power for them to eat when it gets cold.  :^)    There is a lot of extra loom in that power harness which is bundled up in a big blob and zip-tied to the frame.........I'll cut the zip ties loose and look for the "lost" relay underneath.   

I haven't tried to chase the large 12v supply loom back toward the load center in the coach, but I will slide under there again and see if I can follow it.  (I have enjoyed better work environments in my time.)  :^)

BTW- Thanks for all the replies............. ed s