Need help with mystery wire to water pump switch - Fiberglass RV


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Old 06-27-2017, 10:00 PM   #1
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Name: Rob
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Need help with mystery wire to water pump switch

I have a vent hood over the cooktop with a bunch of switches and indicator lights for the tanks on the front vent fan panel. The water pump switch is located there. I like to be sure to know when the water pump is switched on so as not to leave it on by accident when I leave the trailer of go to sleep. I guess I'm just cautious about a leak happening and the pump draining the water tank in an unwanted location! So I decided to replace the small on/off toggle switch with one that lights up when on. I was able to pry the single switch out of the front of the panel with a knife and was surprised to see three wires, as I'd expected to just see two wires, hot and load. The new switch also has a place for three wires (hot, load and ground). It needs a ground for the light in the switch to work and the other two wires are just hot and load. I was perplexed to see 3 wires on the old un-lighted switch but hoped that for some reason it happened to have a ground also, which would have made my task a lot easier. But not so ...no ground wire. One was a hot wire and another a load wire, but I couldn't figure out the third wire. I removed the old switch and hooked up the hot and load to the new switch and it turned the water pump on and off but no light. So I ran a temporary wire to a nearby ground, and voila! The switch lighted when the pump was turned on like it should. I then tested the old switch which I had removed, which was either on or off, but found that it switched the hot lead between the other two terminals! So I am totally puzzled about what would the other wire that receives power when the water pump switch is OFF go to? There was a separate 3 wire harness going only to the water pump switch with a 3 pin plug about 8 inches away from the switch, so it wasn't just some after-the-fact cobbled wiring mess. I just unhooked that third wire and taped the end. I'd appreciate it if anyone has seen such a thing or can even hazard a guess as to why the water pump switch would be an "either or" power switch and what it would power when the pump was in the off position. Thanks for the assistance.
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Old 06-27-2017, 10:21 PM   #2
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I then tested the old switch which I had removed, which was either on or off, but found that it switched the hot lead between the other two terminals!
Rob,

This is a single-pole double-throw (SPDT) switch. The hot wire was on the common leg, so the power was distributed to either A or B.

Unfortunately, more than this I do not know. My feeble brain is not coming up with any ready guess as to what it might be desirable to power when the pump is not running unless it is 3-way switch wiring - do you have a second water pump switch somewhere?

It sounds like you have lots of options to "borrow" ground to run the light from something nearby.
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Old 06-27-2017, 10:57 PM   #3
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Attention Attention

Wiring issues should be taken to somebody that understands wiring, electricity, etc.
Questions about wiring issues answered here are often dangerous or at best no help. Professionals need to see and measure to find the problems. Amateurs can only guess.
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Old 06-28-2017, 08:06 AM   #4
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True professionals are few and far between!

Byron:
I understand your caution, but my experience over years of owning RV's and yachts is that true professionals are really hard to find. More often than not, you end up paying $100 plus an hour for some supposed professional who really knows little more than a lot of us who try to educate ourselves on our systems and fix things ourselves. I might agree with caution when dealing with 120V systems, but 12V DC systems as in an RV are not so dangerous and simpler to understand. An owner who has run across a similar wiring situation will likely be a much more valuable resource than an electrician who will just charge you a bunch to tell you that he has no idea where the mystery wire went. Learning your systems is just part of RVing for a lot of us, and really important when you are out in the boonies!
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Old 06-28-2017, 09:48 AM   #5
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Hermitld

Disclaimer: I am no electrician but play one at home on weekends. Take this advice with a grain of salt, thank you.
I believe the first step in diagnosing a problem is the careful inspection of problem and components. If you don't know a single pole from a double pole switch, maybe it's time to consult someone who does this kind of repair work? It's challenging to investigate new problems but electricity like other energy sources can worry the best mechanic at times. Be careful!
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Old 06-28-2017, 09:57 AM   #6
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Third wire.

The third wire is most likely a ground for the light. The voltage you see on the third terminal is the voltage through the light. You can check this by checking voltage between third wire and 12v. If you read 12v then third wire is ground. The old switch may be lighted with the light burned out.
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Old 06-29-2017, 05:35 PM   #7
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Not knowing where this wire goes and what it is truly intended for you have to trace the wiring run and find the other end.

Remember in some water pump systems there are 2 switches running the same pump. One in the kitchen and another in the bathroom for the shower or commode. Then you would use a 3 wire system with a 3 way switch to run one pump.

Right now the only one who knows why that wire is there is the guy that installed it.
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Old 06-29-2017, 08:38 PM   #8
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Lucky you....Sandstone....

you have a BF and you ONLY got ONE mystery wire...???? Lucky you....I got several.....

I found a bundle under the sink...still a mystery.... see first two pics....I ended using the hot and the neg. for a 12V plug I installed on the outside...immediately beside the AC plug pictured under there.....

Don't know the deatails/year of your BF....mine is a 97....and this was the wiring above the hood fan (last two pics)...it's easy to pop the bottom/floor panels in those overhead compartments and remove/delete the brads.....I removed them all over...giving me good access to those places and "secret compartments" as a bonus....

FWIW the monitors in my trailer have become totally useless....reading half when full on one tank and the reverse on another....it's all over the map....it's a good thing I've been using this trailer for a few years now as I kinda "know" when I need to refill the fresh...and/or dump the grey.......the black is easy as you can just look down the "hole" (with pump off)

good luck to ya....
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Old 06-29-2017, 08:46 PM   #9
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forgot two things....

I leave my pump switch on for long periods....the potential problem you brought up would be awful alright....I might revise my routine in that respect

and I agree with you about working on / figuring out what's what in our trailers.....heck, that's half the fun....maybe more than half...cheers, F
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Old 06-30-2017, 09:07 AM   #10
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you have a BF and you ONLY got ONE mystery wire...???? Lucky you....I got several.....
Boy, at a glance, I could have thought those pictures were from some sort of electronics surplus auction!
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Old 06-30-2017, 09:17 AM   #11
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Quote:
Originally Posted by Franswa View Post
you have a BF and you ONLY got ONE mystery wire...???? Lucky you....I got several.....

I found a bundle under the sink...still a mystery.... see first two pics....I ended using the hot and the neg. for a 12V plug I installed on the outside...immediately beside the AC plug pictured under there.....

Don't know the deatails/year of your BF....mine is a 97....and this was the wiring above the hood fan (last two pics)...it's easy to pop the bottom/floor panels in those overhead compartments and remove/delete the brads.....I removed them all over...giving me good access to those places and "secret compartments" as a bonus....

FWIW the monitors in my trailer have become totally useless....reading half when full on one tank and the reverse on another....it's all over the map....it's a good thing I've been using this trailer for a few years now as I kinda "know" when I need to refill the fresh...and/or dump the grey.......the black is easy as you can just look down the "hole" (with pump off)

good luck to ya....


I love the little yellow pellet in puz3 pic......you find those darn things in all sorts of crazy places for years and years.
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