12V switch question

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tcbro

tcbro

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Jun 3, 2004
375
Hunter 33.5 Middle River, MD
I'm in the process of installing the powerwash system that I bought from this site. The control plate contains a fuse holder and a switch. I believe the switch lights up when the system is powered. I can't be sure because there was no real info in the box. The switch has 3 terminals, one for incoming positive(+) from the fuse, one for outgoing positive(+) to the pump and a negative (-). With the switch in the OFF position the outgoing positive(+) and the negative(-) are connected together but the incoming positive(+) is not connected to anything. In the ON position all 3 terminals are connected. I plan on getting my incoming 12V(+) from the positive(+) buss bar. I will hook the outgoing (+) to the motor and was planning to hook the negative(-) side of the motor and the switch to the negative(-) buss bar. With all 3 terminals connected won't this create a dead short? This doesn't seem right to me. The wiring diagram provided is very basic with only 3 components, the battery, a fuse and the pump motor all in one big loop. All my other equipment is hooked up using breakers, 12V(+) from the pos. buss, other side of the switch goes to the equipment with the (-)return from the equipment going to the neg.(-) buss. What am I missing? Why doesn't this make sense to me?
 
Timo42

Timo42

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Mar 26, 2007
1,042
Venture 22 Marina del Rey
The short you are seeing is

through the light bulb, not a problem. The bulb circuit is parallel to the pump, and will draw only as much current as the bulb needs to light. Tim
 
Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
You have a DPST switch then

DPST double pole single throw (cheap version) You can turn on two thing as once. you do not want to connect the (-) terminal (I can't believe they named it that but whatever) to ground as that would, as you thought, create a short circuit. You can either leave it disconnected and connect the lamp to the terminal that is controling the motor or use one terminal to power the motor and the other to power the indicator lamp.
 
GuyT

GuyT

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May 8, 2007
406
Hunter 34 South Amboy, NJ
Timo42 has it right

If there is an indicator lamp, it would read a very low resistance. Turning on the switch connected the lamp across the 12V to ground. That ground wire can go anywhere convenient since it only has to power up a lamp. To make sure of this, measure resistance from the output of the switch to ground with the switch off. If it measures like a short, it is the bulb creating the path.
 
tcbro

tcbro

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Jun 3, 2004
375
Hunter 33.5 Middle River, MD
Sounds logical

I didn't measure resistance, I only checked for continuity between the terminals. It appears that the rocker on the switch itself is lighted, at least it has a little red plastic window right in the middle of the switch. I won't be at the boat for a while now so I will measure the resistance before I hook it up to see if a lightbulb is indicated. I doubt it's an LED but do they have as much resistance as an incandescent bulb?
 
GuyT

GuyT

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May 8, 2007
406
Hunter 34 South Amboy, NJ
LED /= to incandescent

If you have a digital VOM, there should be a diode measurement. Use that to check LED's with. The digital VOM in the diode setting will forward bias the LED so it actually reads voltage. Typical LED voltage drop is around 2 V using digital VOM. Polarity is important so make sure that the positive of the meter is at the switch and the negative is at the ground. If they are backwards, it will read an open circuit. An incanescent bulb reads resistance in both directions. LED's only bias in one direction.
 
tcbro

tcbro

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Jun 3, 2004
375
Hunter 33.5 Middle River, MD
Unfortunately...

...I only have a cheap analog meter on the boat. The one in my shop is better but it's still analog. Thanks for all of your help. I was planning on getting down to the boat again this weekend but my daughter has had a few things come up so I'll have to wait another week. It makes sense to me that the neg lead is for the light in the switch. I had that thought in the back of my head when I mentioned that the switch was probably lighted. You guys confirmed and help clarify my thinking about it. I'll test before I hook it up but I'm pretty sure I have a handle on it now. Thanks again,
 
F

filthy liberal scum

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May 18, 2004
259
J-boat 42 conn. river
Tom, are you going to be at the boat this weekend?

we are going to be down this weekend,to do some minor maint and go out since we were splashed yesterday. i have a digital meter in my van. i would be glad to help you figure it out. S/V Que Pasa?
 
tcbro

tcbro

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Jun 3, 2004
375
Hunter 33.5 Middle River, MD
Jim,

I was planning on being there but Corinne has a competition in the morning and a party to attend on Sunday afternoon so we'll stay home and I can take care of a few things I have neglected while concentrating on the boat. We sail for NYC on the 21st. Thanks for the offer, glad to hear you're in,
 
F

filthy liberal scum

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May 18, 2004
259
J-boat 42 conn. river
Tom

E-mail me the wiring diagram.I suspect the one of the pos terminals is to go to the pump, the other is to go to the bat. then the neg is to provide a ground for the lamp. the neg on the pump should go directly to your ground buss bar. btw; sure was quiet down there this weekend. maybe the $4.95/gallon gas and $5.25/gal diesel had something to do with it. there still are a lot of empty slips and i did'nt see anyone with a powerboat leave the marina on sunday. can you imagine. $30 in fuel just to get out to hart-miller and back. jim
 
tcbro

tcbro

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Jun 3, 2004
375
Hunter 33.5 Middle River, MD
Jim

There is no wiring diagram but what you describe is exactly what I plan on doing.
 
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