Can you butt connect a thicker wire to a thinner wire?

My alternator wire is terribly short and is barely getting to the alternator and I want to make it longer but I can't find a wire that is as thin as it.

 

Sure you can, maybe solder the two together and put some heat shrink tubing over it.

 

extend it as i had to on my old car. As long as it is the same gauge or close to it is all.

 

Electrically speaking, it is always safe and generally OK to use a larger wire. The only time it wouldn't be a good idea is if you're working with signal wire (to/from ECM)

Make sure the splice is clean, solid, and weatherproofed, and you'll be fine. As EdwardGP stated, soldering & heat shrink are always your best bet. I like to add a coat or two of 3M Scotchkote on top of mine as well.

 

Thats good to know and as for when you connect them thats the way to do it. I have always done that and never have had a issue ever. All the people I know twist them and tape them. I just laugh as they always have issues and wonder why

 

Amen, brother.
When I bought my car, I could not believe what I was seeing when I pulled out the wiring for my cooling fans. You can imagine what my stomach did. If you are an electrical engineer, do NOT click on the picture link!

 

Why? (if you don't mind elaborating on the ECM signal wires)

 

It will make absolutely no difference. Think of a road with traffic. When that 2 lane roads open up into a 4 lane, the traffic flow is going to be improved but It's not going to do anything for the flow of the 2 lane road further back. It doesn't hurt to use a larger wire but it certainly doesn't help either UNLESS there's already an increased current demand on the given circuit which would require upgrading ALL the wiring. I like to use fat wires myself for peace of mind but as long as you've done your homework correctly it makes no difference.

As for the butt connector route, if we're talking about the positive amp wire I would strongly advise against use a butt connector. If you must, make sure you get a really good grade one meant for high current. I once used a crimp on ring terminal on the end of my amp wire and the damn thing burned through a month later from the current draw. It fell off and I somehow managed to make it from my friend's house back to mine running off only the battery.

There have only been a few instances where I have been forced to use crimp connections and even then I still shrink wrap over them as if they were a solder joint. I don't even like using blade connectors for speakers and relays. I solder the wires directly on! Soldering is the way to go. Superior conductance, not as susceptible to corrosion like a crimp connection is and you don't have to worry about the wires pulling out. These are all critical points especially on something as important as the main power feed for the entire vehicle.

 

I agree.
That's why I was curious about the reason for that particular statement from the poster.

Absolutely right.
Thick wires carry high loads and are not easy to connect. I am not saying impossible, just not easy. It is better to replace the whole length of wire than to try to splice it. An alternator supply wire especially is a high-current conductor and if the connection is not perfect, it will cause a small arc and could be a potential fire hazard.

 

Not to mention the increased resistance which brings along with it heat which equals fire hazard that a poor connection could cause on a high amp wire.

 

As far as the ECM thing goes I couldn't wrap my mind around it either. Maybe he's under the assumption that the larger wire would introduce resistance?

I know one thing that people claim NOT to do is use solder on resistance/voltage critical components such as the signal wire to the o2 sensor. However, I have been using this method for quite awhile with no adverse results. If I can put my ohm meter to a 6 inch strand of rosin solder without registering anything, A small dab of it isn't going to do squat joining two wires together.

 

To be honest, I'm not sure of all of the signals that the different ECMs send and receive. It may be completely fine in the f-body realm to use larger wires to/from the ECM.

I was speaking purely theoretically from an Electrical/Electronic engineering standpoint. Increased wire gauge has a slightly higher copper loss / different inherent resistance per foot.

When working with any kind of digital signals if you increase wire gauge, you can induce issues with timing, bit collision, signal degradation, etc. It generally doesn't rear it's head in low speed or short distance applications such as you'd find in these cars, but it's just my $.02. When anything sends or receives a signal to/from any kind of microprocessor, I stick with the same wire gauge that the OEM used.

 

Gotcha.
However, as you pointed out, it is fine in an F-body.
What you are talking about is concern more for HSD applications where latency matters between different transmission lines.

 

Thanks for the responses fellas.