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Old 06-27-2012, 05:27 PM   #15
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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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Old 06-28-2012, 05:50 AM   #16
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I've seen a lot of things that were wired hot to the device and had a switched ground.
I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
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Old 06-28-2012, 09:03 AM   #17
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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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Old 06-28-2012, 10:33 AM   #18
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I find it cheaper to check first than replace cause I guessed wrong.
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Old 06-28-2012, 12:35 PM   #19
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I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
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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Old 06-28-2012, 01:33 PM   #20
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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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Old 06-28-2012, 02:40 PM   #21
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.....latching relays......
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Old 06-28-2012, 03:11 PM   #22
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I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
Look at your Norcold fridg light.
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Old 06-28-2012, 03:35 PM   #23
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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?
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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Old 06-28-2012, 03:38 PM   #24
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Quote:
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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.
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.
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Old 06-28-2012, 03:42 PM   #25
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.....latching relays......
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.
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Old 06-28-2012, 03:44 PM   #26
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Quote:
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I an interested, can you name a few? Not something like a "kill switch" that is a "short to ground".
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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Old 06-28-2012, 03:47 PM   #27
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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.
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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Old 06-28-2012, 03:49 PM   #28
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Look at your Norcold fridg light.


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.
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