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.

Hi,

I wouldnt doubt it if they used #22 (ha ha) as they are always trying to cut costs to maximize profits.

In reality though, a voltage drop in the wire probably causes a bigger voltage drop when there are incandescent bulbs being driven (not saying they are here though). When the voltage on a bulb goes down the resistance goes down as well and starts to draw more current. This causes more voltage drop than a fixed resistance would. It would be interesting to do a short study on this just to get an idea what the total effect on brightness is. That might explain why my headlights were so dim although now i have replaced them with LED type headlamps which dont have that problem.

Arent metric sizes just the diameter in millimeters? I think my old Hyundai schematic had shown those sizes but it's been a while i'd have to look that up again.

 

I wouldnt doubt it if they used #22 (ha ha) as they are always trying to cut costs to maximize profits.

I know from working at Delphi Packard that isn't why they do the smaller wire, it's weight savings. If they could figure a cheap way of doing the, can't recall the real name for it, where you have one wire carrying many signals and the separating them at the different places needed, they would. When I retired they were working toward that. A single big wire going to different ends of the car to provide the current and a single small wire to carry the commands.

 

I know from working at Delphi Packard that isn't why they do the smaller wire, it's weight savings. If they could figure a cheap way of doing the, can't recall the real name for it, where you have one wire carrying many signals and the separating them at the different places needed, they would. When I retired they were working toward that. A single big wire going to different ends of the car to provide the current and a single small wire to carry the commands.

Hi,

So they dont save any money by using smaller wire then?

That is interesting as that seems to imply that there is a performance boost and savings in fuel for the owner which is good to advertise.

That's interesting about the large wire and smaller wires too. Simpler to wire the vehicle so there would be a savings there as well.

 

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.

There are good electrical engineering general practices (tables/NEC) and practical application practices for specific applications (engineering supervision). A car is essentially a moving electrical chassis so 'short' distance interconnect ampacity rules are dandy. I personally think proper overcurrent protection and Crimp terminals being used instead of solder is generally more important for connection reliability.

 

Had a little experience re-wiring a few automotives, Insurance write-off/burn outs.
This was a prize, Jaguar 12cyl XJS. (under the hood fire).
Started first turn of the Key!!
Max.

 

I know from working at Delphi Packard that isn't why they do the smaller wire, it's weight savings. If they could figure a cheap way of doing the, can't recall the real name for it, where you have one wire carrying many signals and the separating them at the different places needed, they would. When I retired they were working toward that. A single big wire going to different ends of the car to provide the current and a single small wire to carry the commands.

@shortbus what you are referring to is multiplexing and we have been doing it now for a number of years. It has proven to reduce the number of wires used, mostly under the dash but has also opened up the door for more creature comforts to be added and even more wiring. It has also created havoc with older technicians trying to adapt to new diagnostic strategies on these vehicles which is now easier and yet more complex (long story).
Regardless, this backup light project is not complex and I am amazed it has gone on for this many posts. It clearly outlines the differences between electronics people and automotive minded technicians. I am not saying that is bad, I have always found it interesting to watch the different approaches. I would have ran my 14 gauge wire days ago and been done. We do not look too much at voltage drop (almost non existent) in a short piece of wire such as this, or heat, strands, material or most other things. Probably because we have done so many and we go to the automotive suppliers and get a roll of primary wire. I do follow the type of wire I use and as @nsaspook has mentioned, proper crimpers and connectors are important. The same holds true I guess when I do anything electronic in nature. I overthink that side of it because it is unfamiliar territory for me in relation to automotive. It is fun to watch the conversation unfold though and see how engineers look at things like this. This is why the automotive forum was important. Anyways, watching to see how the OP ends up doing this. Good thread guys.

 

Probably because we have done so many and we go to the automotive suppliers and get a roll of primary wire.

When I did the auto write offs, I was periodically called in to a local bus manuf. to service the wire strippers/harness producing machines, There was always some 'left overs' after 'Testing' the machine before returning it to service.!

 

@shortbus what you are referring to is multiplexing and we have been doing it now for a number of years.

Thats the word I was looking for. I retiered in 08 and they were near to doing it. The last tool room I worked in was next to the R&D lab and I spent as much time in there talking to the engineers as I could. They were also working toward changing the battery to 42V if I remember right, but it doesn't seem like they made that leap yet, or at least not in my 2018 Equinox. They and LG were doing a bunch of battery testing for EV's too.

 

It has been several months since I last worked on my newest car, replacing the lights driver for the trailer lights. The wires for the rear LED stop and tail lights are indeed more like #18 or #20, but the power wire for that module is about #14, since it needs to power a bunch of lights on the older trailer, which are all incandescent bulbs.
My take on the TS mentioning an additional backup light was that it was a far brighter one consuming a lot more power. Definitely the concern was that it was not a stock light and thus the stock wires might not be able to handle the current.