how to make t splice?

Hi,

In my car I need to connect a daytime running light system. It consists of two 12v relays some wires. Thus, it uses the existing headlights and no extra lights are installed on the car.

I want to connect this device (6 wires in total) to the existing wire harness and it has to be and look professional.

From reading in this forum is seems as soldering is the only way to go. I see a few ways of making the t-splices (I need to make 6 t-splices):

a. Cut the existing main wire. Slip a piece of heat shrink (with glue) onto one end. Remove isolation from 3 wire ends. Solder and heat shrink everything together using the heat shrink.

b. Cut the existing main wire. Slip one solder splice onto one end. Se pic here: Solder splice link Remove isolation from 3 wire ends. Insert 1 wire into one end and 2 wires into the other end and heat to both solder and fuse everything together.

c. Remove 1/2" isolation from main wire (thus not cutting it). Remove isolation from "new" wire, wrap around main wire and solder. Then use something like Scotch 33+.

d. Remove 1/2" isolation from main wire (thus not cutting it). Remove isolation from "new" wire, wrap around main wire and solder. Then use a self fusing tape.

What would you recommend? Maybe even a different solution? What is the experience on 33+ vs self fusing tape?

Thanks in advance,

Lucas

First point is your set-up legal?
On with the headlights really needs a 2 second delay LATCHED via the starter circuit to be legal, check how it's done on Audis, BMW, Volvos etc.
Method B is the best followed by C if you haven't enough cable, having said that, still cut the cable and solder one end to new about 30mm back and sleeve then butt solder and sleeve the two left over.
Adhesive lined heat shrink is by far the best method, I only use it under the hood.Not really needed inside.
I use Scotch 33+, very expensive and hard to get in the UK, I only use it to wrap type C joints.
Self-fusing I assume is what I call "amalgamating tape".
Maybe under the hood (but lets face it you shouldn't be doing connections under the hood, if I was I'd keep them inside an existing sealed relay or fuse box).
I'ts clumsy, in recent years I've only used it as an outside weather protector over heat shrink on things like TV/Sat antenna cable.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I have done my first t splices using the soldering method. I'm quite content with the results. One annoying part is the removing of ½ inch insulation from the main wire. I used a sharp knife to make circular cuts through the insulation ½ inch apart being very careful not to cut the copper. Then I would carefully shave off the insulation in between the two cuts, again being vary careful not to cut the copper. Then I would pry off the insulation with my nails.

One thing I don't like about the soldering method: When soldering, the solder starts moving along the wire due to capillary forces and will often penetrate beyond the insulation. The longer you mess with the actual soldering, the more solder will move in both direction away from the actual t splice area where you really need the solder. The solidified solder makes the wire very stiff for quite a long distance and somewhere else I read that those solder filled wire parts can potentially break because they aren't flexible anymore. Any comments on that?

Prior to my actual installation I made a lot of tests using scrap wires to see how the soldering method would hold up. I realized that it is a delicate job, actually. Of my main concern was the removal of insulation from the main wire: You could easily cut a few of the tiny single wires reducing the amount of current draw. Shaving off the insulation lengthwise was not so problematic but very time consuming.

How do you go about doing those t splices? Is it really a very time consuming delicate job or do you use a special tool for that purpose?

Lucas