Using fuse box spare fuse

Keep in mind there are at least 2 12 volt fuse panels in motorized rigs- the house fuse panel will not have any switched circuits, only the chassis fuse panel. Normally the chassis fuse panels are well marked with which are switched "ign", though there will usually be 2 versions- on with the key in the run position, and on in both run and acc position. The chassis fuse panels will normally be under the dash, and often there will be an under hood one as well.

westend wrote:
Do you have a test light or a meter?
Edit: you can also make your own tester using two wires and a 12V bulb or any 12V device. You could even use your new monitor. Attach one wire lead into each of the opposing blade sockets. With the two stripped wires from the fuse location held in your hand, touch the (-) and (+) to the contacts of the device or bulb you are using to test.

IMO, anyone either working on vehicle or RV electrical systems should have a meter. They are cheap enough, now, that there is no excuse not to have one. Harbor Freight sells a variety of them, the cheapest either being $4 or free when offered as a promotion..

Not sure I am understanding this correctly, so please excuse if I have it wrong. Are you suggesting that both test wires be hooked to either side of the fuse socket? That would be 2 positive feeds. One of the test wires should be connected to ground (-) and one to the fuse socket (+). Using the backup monitor as the tester could result in damage to it. I agree 100% to go to Harbor Frieght or big box hardware store and buy a cheap meter.

Do you have a test light or a meter?
Edit: you can also make your own tester using two wires and a 12V bulb or any 12V device. You could even use your new monitor. Attach one wire lead into one the blade sockets. Attach the other wire to a good ground. With the two stripped wires from the fuse location and ground held in your hand, touch the (-) and (+) to the contacts of the device or bulb you are using to test.

IMO, anyone either working on vehicle or RV electrical systems should have a meter. They are cheap enough, now, that there is no excuse not to have one. Harbor Freight sells a variety of them, the cheapest either being $4 or free when offered as a promotion..

The only way you'll know for sure is to probe them with a meter. Some will likely be on when the iginition is on, and others will most likely be continuously on.

If you don't know how to use a meter, it would probably be best to get some professional or trusted friend's help.