adding electrical items for dummies

Just want to make sure I do this right, I am not familar with the way current flows in a DC circuit (I know AC). Need to add a single light rear license plate light. Have the wire, have the light, not sure how to rig it up best. I'm sure it's best if it is constantly "ON", for legal reasons, but I don't want to hook it up so that the light is on when the truck is shut down, draining the battery. Should I hook it in with a single switch in the cab?

Anyone got a circuit diagram the way it should be wired?

License plate lights are normally on only when the taillights are on. Tap into wire number 21 at a tail light and you will have power whenever your tail lights are on. Wire # 21 is 24volts positive(taillights). Does your license plate light have one or two wires? You can get a wire Adaptor/Splitter that is mil spec, that will go right in-line at the taillight connection near the air valve. You can make it look like it's original that way.
If your new light has only one wire then it is grounded through the mounting screws, if it has two wires be sure to ground the wire that is connected to the bulb socket outer housing. The positive wire goes to the center of a single filament bulb socket. Of course, use a 24volt bulb!
Saturn Surplus Adaptor/Splitter.... http://saturnsurplus.com/electrical/adpt.htm

One of those things you will probably NEVER need to know AND has absolutely nothing to help in wiring in a tag light.
Which BTY I was once told by a Georgia State Trooper that he didn't care if you didn't have one. If he wanted to read the tag he COULD. Wayne

From: Frank Berauer, Technology Transfer Engineer Microelectronics
When electricity was discovered, nobody knew how it works and electrons were unknown. So the scientists just defined one of the poles as "positive" and said that the current is flowing from positive to negative. That still is the definition of an electrical current's flow direction.
However, later scientists discovered that in most (but not all) materials current is carried by negatively charged electrons, which travel from negative to positive. The electron flow is thus opposite to the current flow. In some materials (e.g. electrolytic solutions) the current is carried by positive ions, which travel in the current's direction. And in semiconductors there can be currents of negative or positive carriers, depending on the doping.

Greetings from Singapore, Frank Berauer

tag light

O.K. No tag light 20.00 ticket, no tag 80.00 ticket, oversize and no insurance get in back of the car! We'll teach these dang people, yet,

papercu said:

Which BTY I was once told by a Georgia State Trooper that he didn't care if you didn't have one. If he wanted to read the tag he COULD. Wayne

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Here in Virginia, if a tag isn't illuminated when the rest of the lights are on, it will fail the State Safety Inspection. I know, I am a State Inspector.

Doghead is right on.

Most tag lights ground when you mount them and the wire is a positive lead that you tap into the service light circuit.

Good deal - I built the light mount and license plate mount today, will wire it up to #21 tomorrow. Thanks guys!

Very informative, but which truck are you referring to when you say wire #21 (is it universal?) I am trying to do this for my HMMWV. Where can I find wiring diagrams (which TM, link, etc)? I purchased a LED light (which says DC 12/24v - 10w) which I hope will work, and it does have a separate power and ground wire.

Thank you in advance.

Wiring in M series vehicles is standardized according to this chart: http://olive-drab.com/od_mseries_circuits.php

This is a good one to print out and keep in the toolbox.

Kurt

papakb said:

Wiring in M series vehicles is standardized according to this chart: http://olive-drab.com/od_mseries_circuits.php

This is a good one to print out and keep in the toolbox.

Kurt

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Awesome, thank you! I tapped into the #21 and grounded on the taillight mounting bolt and it worked with no problems.

Next question if I may. I am installing an electrical battery cutoff that needs to connect to an accessory wire that is only active/powered when the motor/alternator is running to avoid cutting off the electrical supply while driving (It cuts off when voltage drops below a certain point to prevent battery drainage). I was thinking just connecting it to a light, but that relies on me switching it on and off at the right times. So, is anyone aware of any power sources that are only on when the engine is running and that is near the battery compartment? I searched the wiring chart, but doesn't specify in this way.

Thanks in advance for the help.

Please do not cross post questions(post in more than one thread).

New Hampshire doesn't require any alterations to a motor vehicle other than its original factory items , NO TAG LIGHT NEEDED. State Troopers answer the same, if the are curious about your plate , they just pull you over

confused..... doghead: are you speaking to me? I didnt post this question in any other thread or are you saying I need to create a whole new thread for it?

kapkanimd what your proposing is an automatic battery disconnect but what your suggesting doing will only give you headaches. Here's a much better way to do what you want: https://www.batterystuff.com/battery-products/switches/

Kurt

papakb said:

Wiring in M series vehicles is standardized according to this chart: http://olive-drab.com/od_mseries_circuits.php

This is a good one to print out and keep in the toolbox.

Kurt

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Every once in a while the military does it right. And the wire numbers on M series vehicles is one of them. Gen sets also!

Seems very similar to what I have, but regardless, I already have it so I am going to give it a try. I really got it for security as it has a manual cut off switch that I can disable the batteries when I leave the car and turn it back on with a button.