Basic12 volt wiring question help please

If you had a home made voltmeter like this, it won't read reverse
Costs about 3 bucks to make.

Hotel fuses are NEVER EVER supposed to be installed on the earth (negative) side. Instead of connecting a 12-volt test lead ground clip "to the other wire" connect the ground clip to the rig's chassis. No light no power. Light: You have found + positive.

Some Fantastic fans have electronics in them, and ALL electronics, including the fridge are polarity sensitive, meaning you can very easily blow things up. If this is unfamiliar territory for you, find a friend that knows what they are doing and buy them a beer.

Ava wrote:
Use a basic volt/ ohm meter and check the voltage. It will read the voltage either way but will show a negative sign in front of the voltage if you have the red lead on the ground.

Thanks you very much...I never knew that. Will be looking for minus sign tomorrow.

SCVJeff wrote:

path1 wrote:
I want to confirm my wires are fused is on the positive side.

Vent fan in bedroom pos is gray and ground is white. At other end of TT white is pos and gray is neg.

I can live with wires changing colors behind the walls or ceiling but want to make sure all fuses is on pos side. In case other projects or whatever.

How would you... test to make sure pos is the fused side?

What I would do is head to Harbor Freight or Sears and buy a digital volt meter. Why are you fiddling around without one?

How would a volt meter tell me which side is fused?

(edit part) posting above gives answer. Never knew about - sign on volt meter.

Use a basic volt/ ohm meter and check the voltage. It will read the voltage either way but will show a negative sign in front of the voltage if you have the red lead on the ground.

Being this a "reversible" fantastic fan and 12 volt, maybe I got wires crossed? Fan is running the wrong way. When I have "air" out, it's pulling air in. But at other end of TT in the kitchen, wire colors are just the opposite and runs the right way. I know if have to wire to the function of the wire and not color.

Tomorrow I'm going to disconnect pos side at battery and hook up one side of extension cord to battery and other end to top spade of each fuse holder and a continuity tester to lower side. Which would complete the circuit, and tester should sound off, if fused on pos side. Battery will still be hooked up to neg side. If neg side is fused, (by mistake by OEM) continuity tester will not sound, because circuit is not complete.

At least that's my thinking. (Which is not that good with elec)

path1 wrote:
I want to confirm my wires are fused is on the positive side.

Vent fan in bedroom pos is gray and ground is white. At other end of TT white is pos and gray is neg.

I can live with wires changing colors behind the walls or ceiling but want to make sure all fuses is on pos side. In case other projects or whatever.

How would you... test to make sure pos is the fused side?

What I would do is head to Harbor Freight or Sears and buy a digital volt meter. Why are you fiddling around without one?

Never-mind.......misread the 'question'

I assume you have a centralized fuse panel for the 12V circuits? If so, that's connected to the positive battery lead, and that's where the fuses are. You can verify by removing the fuse for the fan circuit.

More generally, the best way I know to determine which lead is fused is to find the fuse and remove it and see which lead is now dead. That said, it should always be the positive lead, as close to the battery or distribution point as possible, and the fuse sized according to the wire size (or possibly smaller in a few cases, but never larger).