My apologies, I did misread the part about the brake lights. Still need more info on the install.
As for modules and addresses, keep in mind that the industry is trying to drive independent shops out of business and keep shop repair times down. By placing everything on the BUS, everything can be monitored and diagnostics are kept to a minimum because it will all be self-diagnostic (haha) and technicians will be parts replacers. This is the goal right now and if you don't believe it, look at some VW models and the hierarchy of their wiring systems. We are not far off from self-diagnosing vehicles.

I REALLY hope NOT!! The other side of self diagnostics is systems that refuse to accept anything except OEM parts. That will be the end of aftermarket reasonably priced electrical parts and even just repairing electrical assemblies. And it is offensive to consider paying a parts changer the same rate as a doctor or lawyer, and not even being able to be allowed to do the work myself.

 

I already provided the information about wires sizes 16, 14, and #12, with currents not wattages. And in each case the drop in the fuse will be greater than the drop in the wire at the max current I listed.

Hi,

And?

 

So using the the charts given below, the information looks like it's contradicting it's self significantly.

A) https://www.powerstream.com/Wire_Size.htm
B) http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/

Chart A says 3.7 max for power transmission or 22 amps for chassis wiring. I don't know the difference between the two, but I'm assuming the 3.7 for power transmission is what I'm looking for. However, Chart B says 10 amps for a 7 foot run.

This is the type of confusion I keep getting into. Which amp rating do I go by? I'm using 16 AWG to conform to the standard wiring of the trailer connectors, since I'm merging a flat 4-pin connector into an 8-pin connector to consolidate the wire runs as I add stuff to the back. I'm planning on splicing a wire from the reverse backup lights to run to a waterproof relay to turn on the "upgraded" back up lights that's mounted on my spare tire mount.

I'm in Hawaii, so extreme temperatures is not that big of a concern. Than and most of the wire will be run outside of the body along the jeep frame in the black split wire conduit. The conduit and the wires would come from an auto shop like O'Reilly. So, the quality of the material would be automotive. So, thick wire coating will be on the wire.

 

The current ratings for each size are based on the heating effect, and the heating is caused by the power dissipated in the voltage drop of the wire. So operation at current levels that don't cause much heating also do not cause much voltage drop.
Is that added backup light one of those really high power incandescent ones, with the intention of getting tail-gaters to back off? That may require an additional larger wire. Long ago I met a chap whose high beam lights had been replaced by a pair of F-111 landing lights. They looked bright against the noonday sun on a clear day, and drew LOTS of amps.
If you are using any LED automotive lights they mostly include a circuit to control the current and so a bit of voltage drop may not have any effect at all, at least on many types.

 

Sorry I didn't put my chart on here. It can be trusted, I have used it for years in the automotive industry and it errs on the side of safety/caution. If you are using a relay, I would use 16 gauge for the control circuit and 14 gauge GPT or GXL rated wire for the load circuit. If it is more than 15 amps, use the chart accordingly.
If you are using convoluted tubing for protection, if it is for off-road use (mud/water/swamps etc) use one piece convoluted tubing without the slit. If it is regular use driving, use the tubing with the slit but make sure the slit is facing downward so it does not collect dirt/water/mud etc.

 

Mostly the fools have not gone to that poor choice of a digital buss to control all of the items. I actually ran into it when working with production line testers for GM vehicles.

You must have stopped working for GM before I did. Everything has a module and is on the buss. It's nowhere near as bad as Ford though. They have everything with a separate module and that module is tied to the VIN. You need to go to the dealer to work on them. Every turn signal on each corner has it's own module!

 

The current ratings for each size are based on the heating effect, and the heating is caused by the power dissipated in the voltage drop of the wire. So operation at current levels that don't cause much heating also do not cause much voltage drop.

Where do you come up with that? It's voltage drop not heat. I worked where they made the wire, terminals, connectors, many of the blocks in GM cars. And most of the engineering was done there too. It was all about voltage drop.

 

Sorry I didn't put my chart on here. It can be trusted,

That's pretty much the same as the one in my link. http://www.offroaders.com/technical/12-volt-wiring-tech-gauge-to-amps/

 

If I'm assuming, your running one wire and the chassis is ground. Backup lamps are rather intermittant. Generally, you won't find less than 16AWG in a vehicle. There is generally 2 strandings available too, but there is also an automotive class of wires. I don;t know why they use copper and not tin plated copper.

The tables assume 2 wires to the load and the distance to the load, thus the calculators use 2x the distance to get the length of the wire. With the automotive chassis as the return, you would use the distance/2.

If you were using a connector to a trailer, you could say add an extra 5 feet. Being anal, you could look up contact resistance of the connector and add that in too. The primary job of the fuse is short-circuit protection or to protect the wiring

There are specific ground points in a vehicle as well.

One end of your load is the chassis. That part of the wiring is negligible and you can assume 0 ohms.

 

If I'm assuming, your running one wire and the chassis is ground. Backup lamps are rather intermittant. Generally, you won't find less than 16AWG in a vehicle. There is generally 2 stranding available too, but there ia an automotive class of wires. I don;t know why they use copper and not tin plated copper.

The tables assume 2 wires to the load and the distance to the load, thus the calculators use 2x the distance to get the length of the wire. With the automotive chassis as the return, you would use the distance/2.

Ah... ok, that makes more sense. Yes, I'm grounding to the chassis. At least where I can.

What's the diff on copper and tin plated?

 

Hello again,

Probably the main concern is cost of installation. If you cant afford 15 feet of #14 AWG wire then you probably cant afford to run the vehicle in the first place.

Here is another table. The max current values are shown based on 600 circular mils per amp. You can double the ampacity if you venture into the 300 cm/amp region which probably is not recommended for automobile applications.
The resistance is also shown. The rule for heating is simple: For every 25 degree C temperature rise increase the resistance by 10 percent. So for example 10 feet of the #16 AWG wire would have the following resistances based on the associated temperature rises shown:
0.040, Tr=0C
0.044, Tr=25C
0.048, Tr=50C
0.052, Tr=75C
0.056, Tr=100C
This of course assumes the wire insulation, sheathing, and surrounding components could all take the temperatures shown when added to ambient.

 

Probably the main concern is cost of installation. If you cant afford 15 feet of #14 AWG wire then you probably cant afford to run the vehicle in the first place.

That's a rude assumption... especially since I already stated why I'm not using a larger gauge of wire. If it was practical and safe, I'd run 0AWG for the backup lights. I've read everyone's post. It'd be a nice courtesy for you to do the same.

 

Another thing that hasn't been mentioned, is the number of strands in a Automotive wire. I can only talk for what is used in GM cars and trucks, but other than battery cable they(GM) use 19 strands, no matter what the gauge. Some of the wire sold in a parts store isn't really car wire but just industrial machine wire in a small coil. It is fewer strands, that makes it stiffer than real car wire, flexibility is why GM uses 19 strands.

 

What's the diff on copper and tin plated?

Radio-Shack used to sell just copper wire, no plating. It's difficult to solder to after it oxidizes. I didn't buy the stuff.
House wiring isn't plated.

Electrical instrument wiring is and that plating is tin. Silver plated copper tubing in RF amplifiers.

Probably tin plated is better for automotive. See http://www.bestboatwire.com/marine-wire/marine-primary-wire

 

Another thing that hasn't been mentioned, is the number of strands in a Automotive wire. I can only talk for what is used in GM cars and trucks, but other than battery cable they(GM) use 19 strands, no matter what the gauge.

I kinda mentioned it. You mentioned it MUCH better. I liked the lower stranding for control cabinets I built because I didn't want sagging. I also used ferrules because of the "screw terminals". Not all screw terminals have a "wire protector" which prevents the stranding from getting damaged by the crews.

 

Probably tin plated is better for automotive.

I don't know about that but if it was Packard would have done it. They made the wire themselves, started out with ~5/16" copper rod and drew it down to what was needed the combined the strands and then extruded the insulation on it. They even made their own electrical tape in house, starting with rolls of plain plastic sheet, some got adhesive some didn't. They called the non adhesive stuff loom tape, so repairs could be made later if needed. But that was before the corrugated loom tube they use now, they made it too.

 

Looks like 3% was a good guess: See http://www.bestboatwire.com/voltage-drop-calculator

They called the non adhesive stuff loom tape, so repairs could be made later if needed. But that was before the corrugated loom tube they use now, they made it too.

Found loom on spark plug wires. I have no idea if that was factory. This thread is a strange topic for AAC,

 

That's a rude assumption... especially since I already stated why I'm not using a larger gauge of wire. If it was practical and safe, I'd run 0AWG for the backup lights. I've read everyone's post. It'd be a nice courtesy for you to do the same.

It was not directed at you, it was just a general statement. You took it personally.
It's a comparative...one cost against another. The price of a short length of #14 gauge wire is very very low compared to the price of operating and maintaining a vehicle of any kind in this day and age.
Feel free to use any size wire you want though. It's always up to the person who wants to do the mod, not up to me unless it is my vehicle. I would probably opt for #12 myself just for the durability as well as the current handling capability.

 

Post 38 makes the point that I tried to present much earlier, that the very small additional cost for bigger and better wire that will certainly not heat as much nor have as much voltage drop is the far better way to go. And realize that heating is caused by the voltage drop, and so minimizing one minimizes the other.

 

Bet none of you supporting a big/large wire for any of the lighting in the rear of a car have actually looked in your own car, to see the size of the wire used. I'm betting, from experience, That you'll find that it is a metric gauge and is slightly smaller than 16 AWG although I don't know or understand the metric wire gauge system. The wires to an electric fuel pump which draws more amps than the lights is only a metric size that is between 16 and 14 AWG.