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06-27-2012, 04:27 PM
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#15
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Senior Member
Join Date: Sep 2011
Posts: 168
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I also used to have difficulty with meters. It's the best tool in your box.
Put the multi meter rotating dial on DC volts, use a scale above what you think the volts will be. There will be two probes one labeled + plus (positive) normally red the other - minus (negative) black.
Put the two probes on the device (it does not matter which one you put where) and measure voltage. Note where the positive probe touches. If you get a plus voltage the positive probe is on the positive terminal. If you get a negative volts the positive probe is on the negative terminal. Reverse the two probes and the polarity should change.
Dick
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06-28-2012, 04:50 AM
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#16
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Senior Member
Join Date: Jul 2008
Location: Sarasota, Florida
Posts: 606
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Quote:
Originally Posted by Dunner
I've seen a lot of things that were wired hot to the device and had a switched ground.
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I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
__________________
2004 Damon Escaper 4076
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06-28-2012, 08:03 AM
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#17
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Senior Member
Join Date: Jun 2011
Location: Phx, Arid~zona
Posts: 11,106
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Not I can't, but you are making my brain hurt trying. I did find it strange, but this not something I put in my memory bank or keep spreadsheet on. Sorry.
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06-28-2012, 09:33 AM
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#18
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Senior Member
Join Date: Oct 2005
Posts: 1,224
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I find it cheaper to check first than replace cause I guessed wrong.
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06-28-2012, 11:35 AM
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#19
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Senior Member
Vintage RV Owners Club
Join Date: Apr 2012
Location: Lyons, GA
Posts: 769
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Quote:
Originally Posted by randco
I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
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How about you cars interior lights? The courtesy light at you rv's door? Your horn? All work by grounding. Engine oil warning light?
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06-28-2012, 12:33 PM
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#20
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Senior Member
Join Date: Jun 2011
Location: Phx, Arid~zona
Posts: 11,106
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I was trained by the army in 1966 for electronic test equipment repair. Analog/digital meters, scopes, analyzers, etc. I continued doing so at Motorola after I got out. I can't remember every piece of equipment I've repaired and calibrated.
Here's a good example of grounding a device. My Dodge Ram ECU applies a ground(switch) to the sensors, injectors, etc to monitor and actuate them. They do this so if you accidentally ground a sensor wire or a pin on the ECU, it doesn't damage it.
I don't know why I have to defend myself.
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06-28-2012, 01:40 PM
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#21
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Senior Member
Join Date: Aug 2011
Posts: 1,546
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.....latching relays......
__________________
2017 F350 Lariat Diesel Dually, White, Hitch Kit.
2013 Dutchman Voltage 3200 Epic II 5th wheel.
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06-28-2012, 02:11 PM
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#22
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Senior Member
Join Date: Sep 2009
Posts: 180
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Quote:
Originally Posted by randco
I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
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Look at your Norcold fridg light.
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06-28-2012, 02:35 PM
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#23
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Senior Member
Join Date: Jul 2008
Location: Sarasota, Florida
Posts: 606
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Quote:
Originally Posted by 87Rockwood
How about you cars interior lights? The courtesy light at you rv's door? Your horn? All work by grounding. Engine oil warning light?
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They work because the circuit is completed via the gound. But the switch is in the positive wire before the load. The switch is not in the ground wire after the load.
__________________
2004 Damon Escaper 4076
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06-28-2012, 02:38 PM
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#24
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Senior Member
Join Date: Jul 2008
Location: Sarasota, Florida
Posts: 606
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Quote:
Originally Posted by Dunner
I was trained by the army in 1966 for electronic test equipment repair. Analog/digital meters, scopes, analyzers, etc. I continued doing so at Motorola after I got out. I can't remember every piece of equipment I've repaired and calibrated.
Here's a good example of grounding a device. My Dodge Ram ECU applies a ground(switch) to the sensors, injectors, etc to monitor and actuate them. They do this so if you accidentally ground a sensor wire or a pin on the ECU, it doesn't damage it.
I don't know why I have to defend myself.
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I think that gounding a device is a little different than placing a switch in a ground wire in a DC circuit or in a neutral in a 120V circuit.
__________________
2004 Damon Escaper 4076
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06-28-2012, 02:42 PM
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#25
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Senior Member
Join Date: Jul 2008
Location: Sarasota, Florida
Posts: 606
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Quote:
Originally Posted by BCooke
.....latching relays......
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Nope, the NO Start switch and the NC Stop switch are wired in series to the coil of a relay. The NO set of contacts in the relay are wired in parallel to the NO Start switch.
__________________
2004 Damon Escaper 4076
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06-28-2012, 02:44 PM
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#26
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Registered User
Monaco Owners Club
Join Date: May 2009
Posts: 3,198
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Quote:
Originally Posted by randco
I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
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The most common is the courtesy lights on car doors.
They run hot to the lamps, and a single wire to the pin switches in the doors.
Door open equals pin hits ground equals light
A lot of circuits switch the ground side. It doesn't matter a whit to the load, and can often make things easier, or cheaper on the manufacturer.
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06-28-2012, 02:47 PM
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#27
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Senior Member
Vintage RV Owners Club
Join Date: Apr 2012
Location: Lyons, GA
Posts: 769
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Quote:
Originally Posted by randco
They work because the circuit is completed via the gound. But the switch is in the positive wire before the load. The switch is not in the ground wire after the load.
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No the switch is on the ground side. Take the wire off the door switch and ground it. Look my interior lights came on. Take the wire off the oil pressure switch and ground it ,oh look my "oil" light is on.
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06-28-2012, 02:49 PM
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#28
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Senior Member
Join Date: Jul 2008
Location: Sarasota, Florida
Posts: 606
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Quote:
Originally Posted by bjsheldon
Look at your Norcold fridg light.
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http://i50.tinypic.com/2d1pp38.jpg
Sorry, I don't have a Norcold. The wiring in my Dometic shows that the switch is in the +12 volt line, not the -12 volt line or ground.
I think this is fairly typical wiring.
__________________
2004 Damon Escaper 4076
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