tap into a cable - safely

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fiksal
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tap into a cable - safely

Post by fiksal » Fri, 22. Dec 17, 18:54

Howdy,

so, apparently, what I am planning to do is not the safest.

here's what I want - I need to tap/attach a cable into a rear lights cable in my car.

What's the best and safest way to do it? As in, after I strip part of it and tie it, should I really solder it? what should I insulate it with?

I was going to to strip small section, tie it (possibly running through first) then use electrical tape. The last part, I am reading, is specifically not safe part.

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Re: tap into a cable - safely

Post by Observe » Fri, 22. Dec 17, 19:10

fiksal wrote:Howdy,

so, apparently, what I am planning to do is not the safest.

here's what I want - I need to tap/attach a cable into a rear lights cable in my car.

What's the best and safest way to do it? As in, after I strip part of it and tie it, should I really solder it? what should I insulate it with?

I was going to to strip small section, tie it (possibly running through first) then use electrical tape. The last part, I am reading, is specifically not safe part.
Lacking some sort of crimp connectors and the tool to go with it, you would probably be best soldering the wires. The main thing is, you want a good metal-to-metal connection that isn't going to loosen contact over time. Believe it or not, crimping can actually result in a 'better' connection than soldering if done right.

If the wires aren't connected well, they present resistance to current flow, and that leads to heat - which can lead to fire - although if it's just tail-lights, you probably don't need to worry about that too much, because the amperage won't be very high.

If it were me, I'd solder and then cover with electrical tape or better yet, heat shrink tubing which is used for this sort of thing.

Lacking soldering or crimping, you could just use simple twist connectors available in any electrical supply shop.
Last edited by Observe on Fri, 22. Dec 17, 21:15, edited 2 times in total.

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Post by burger1 » Fri, 22. Dec 17, 21:13

Why? What do you hope to accomplish?

Increasing the resistance (adding stuff) might lead to other problems. Vehicles can be quite sensitive. I have done stuff the way Observe says too but it was working on motors and stuff where a bit of extra resistance and stuff didn't really matter.

There's probably a reddit sub

https://www.reddit.com/r/AskElectronics/

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Post by pjknibbs » Fri, 22. Dec 17, 21:35

The problem with using electrical tape to insulate it is that cars aren't generally the driest of environments, and it's very easy for water to seep under the tape and corrode the wires inside. Does the tap have to be taken from the middle of the cable? If you could take it from the connector at the end it would be a great deal easier to replace when it stops conducting electricity due to corrosion in five years' time.

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Re: tap into a cable - safely

Post by Morkonan » Fri, 22. Dec 17, 21:56

fiksal wrote:Howdy,

so, apparently, what I am planning to do is not the safest.

here's what I want - I need to tap/attach a cable into a rear lights cable in my car.

What's the best and safest way to do it? As in, after I strip part of it and tie it, should I really solder it? what should I insulate it with?
Use a connector that is built for this purpose. You'll find many types at auto shops, used for wiring up power for towed trailers.

IMO, if it's frequently exposed to harsh weather, road salts, etc, use the connector and then coat it with and electrical insulating coating if you're worried about it. It's basically "goop" used for exterior hard-weather connections, is weatherproof, does not "crack" and is non-conductive. It's applied with a brush. (Think old-timey "creosote", but now much safer.)
I was going to to strip small section, tie it (possibly running through first) then use electrical tape. The last part, I am reading, is specifically not safe part.
What are you trying to do? For instance, if there's going to be any additional load on it, then expect blown fuses. Check your auto's manual to see if it has instructions for installing accessory plugs/tow gear. Or, just look online for instructions on how to install a power-plug on a car that is towing a trailer, which is basically what you're doing. (Note: It should take the extra load of a couple of extra trailer brake lights and turn signals, but that's about it, I would think.)

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Re: tap into a cable - safely

Post by fiksal » Fri, 22. Dec 17, 22:24

Observe wrote: Lacking some sort of crimp connectors and the tool to go with it, you would probably be best soldering the wires.
The main thing is, you want a good metal-to-metal connection that isn't going to loosen contact over time. Believe it or not, crimping can actually result in a 'better' connection than soldering if done right.
I can go with crimping. Is there a crimp thingy for a T shape of connection?

EDIT: something called a "T tap" perhaps?
Observe wrote: If the wires aren't connected well, they present resistance to current flow, and that leads to heat - which can lead to fire - although if it's just tail-lights, you probably don't need to worry about that too much, because the amperage won't be very high.
Understood.
Observe wrote: If it were me, I'd solder and then cover with electrical tape or better yet, heat shrink tubing which is used for this sort of thing.

Lacking soldering or crimping, you could just use simple twist connectors available in any electrical supply shop.
ah okay, that's what it's called - "heat shrink tubing". I read that's a much better alternative to electric tape.

burger1 wrote:Why? What do you hope to accomplish?
I am mounting rear view camera, and I need power (and trigger) for the camera itself. It's suggested that I find the rear (specifically: backup) cable.

pjknibbs wrote: Does the tap have to be taken from the middle of the cable? If you could take it from the connector at the end it would be a great deal easier to replace when it stops conducting electricity due to corrosion in five years' time.
Interesting. No I suppose the tap doesnt need to be in the middle; just the videos I saw showed to do it that way.
You think take apart the 'end' instead? Hmmm...and how would I attach everything there?
Morkonan wrote: Use a connector that is built for this purpose. You'll find many types at auto shops, used for wiring up power for towed trailers.

IMO, if it's frequently exposed to harsh weather, road salts, etc, use the connector and then coat it with and electrical insulating coating if you're worried about it. It's basically "goop" used for exterior hard-weather connections, is weatherproof, does not "crack" and is non-conductive. It's applied with a brush. (Think old-timey "creosote", but now much safer.)
Dont think salt gets into that area of the trunk, but moisture probably does.

Alright, I'll google some auto shops.


Morkonan wrote: What are you trying to do? For instance, if there's going to be any additional load on it, then expect blown fuses. Check your auto's manual to see if it has instructions for installing accessory plugs/tow gear. Or, just look online for instructions on how to install a power-plug on a car that is towing a trailer, which is basically what you're doing. (Note: It should take the extra load of a couple of extra trailer brake lights and turn signals, but that's about it, I would think.)
A rear view camera; I need to wire its power.

Do trailer lights come with easy to use adapters, I wonder?

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Re: tap into a cable - safely

Post by Morkonan » Fri, 22. Dec 17, 22:35

fiksal wrote:...Dont think salt gets into that area of the trunk, but moisture probably does.

Alright, I'll google some auto shops.
If you can't find it at an auto-shop (the coating), you can find it in any DIY store in the electrical dept.
A rear view camera; I need to wire its power.

Do trailer lights come with easy to use adapters, I wonder?
Ah, then you may need constant power, so be sure whatever wire you're using has it. You don't want your camera going on/off/on/off every time you use your turn signal. :)

There should be some instructions included with that camera. Use the 'net and google up some "how to's." There has to be some.

Yes, light sets for trailers have connectors and such so you can add plugs to the towing vehicle. But, this may not be what you want for that camera.

You may be able to tie-in to the power supply for the trunk light. That will be switchable at the latch, so it should have constant power during vehicle operation. Just be sure it doesn't have "always on," though, since you wouldn't want a dead battery.

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Post by Alan Phipps » Fri, 22. Dec 17, 23:07

Car accessories that have instructions saying 'Attach to the existing xxxx cable in the car wiring loom' may come with a small loom cable attachment device similar to this.

These are like a small T shaped press-clamp that in pressing closed push sharp connector blades into both sides of the existing and new cables that just slightly nick through the cable insulation and lightly touch and hold the metal cores on both sides, so making the connection.

These are intended for use inside the car internal bodywork where the joint to the loom is largely protected from salt and moisture, etc. No additional insulation is needed once the attached cover is clicked over it and the rigid body of the connector supports the joint area.

It is recommended that you get the cable choice and location right first time as moving them once attached is not a good idea.
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Post by Avis » Fri, 22. Dec 17, 23:46

I've wired up a few towbar and lighting sockets on cars, the options are as far as I'm concerned.

1) Scotch locks, plastic crimps that tap into an existing cable, I don't like these personally, they are fine for a temporary join and I've never had one fail tho that might be because I don't trust them so replace them soon after.

2) Strip the cable back slightly and solder onto it then tape it off (moisture is possible but if you're getting that much water in your car get a boat, a car shouldn't get that wet inside to be a real problem so long as the wiring is behind the trim.

3) disconnect the wire from the light cluster itself, solder or crimp an extra cable from there, this way is far neater than the above but more of a faff on.

4) get a set of connectors to make your own wiring harness/loom, if the car already has a modular wiring loom great get the male and female put the spur wiring from that and plug it back in, but even for common cars short of rummaging round a scrapyard finding the right connectors can be a pain in the teladi.

I tend to just strip the cable, solder in and wrap, try to do all the joins in the same area so you can bundle them together and make sure they are wrapped and secure behind the interior trim.

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Post by Morkonan » Sat, 23. Dec 17, 01:31

Scotch-locks, crimp/splicers are always an "ungood choice" for wiring, IMO. They're quick and easy to use, but often fail compared to strip-and-crimp, solder, etc, methods.

I've got a big compartmented box full of different cabling/wiring connectors and have more of those quick-crimp/splice jobbers than anything else because I never use those for anything.

PS - I don't do anything related to wiring "professionally" and don't make wiring harnesses for automobiles at all, really. At best, I can say I've worked on wiring in car radios/stereos and speakers and the like, maybe fixing some wiring harnesses long ago when I was a teen/young-adult. That's it. I have done some stuff around the home and outside it, of course, including going a bit further than some in regards to fixing home appliances. Since that involves tearing something apart and putting it back together again in order to figure out how it works, it's something I have actually enjoyed doing. :)

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Post by fiksal » Sat, 23. Dec 17, 01:52

Alan Phipps wrote:Car accessories that have instructions saying 'Attach to the existing xxxx cable in the car wiring loom' may come with a small loom cable attachment device similar to this.
ah, thanks. Those are the things I was thinking of.
Morkonan wrote: Ah, then you may need constant power, so be sure whatever wire you're using has it. You don't want your camera going on/off/on/off every time you use your turn signal. :)

There should be some instructions included with that camera. Use the 'net and google up some "how to's." There has to be some.
The idea is to hook the camera up to rear, specifically, backup lights. This way when the car is in reverse, camera has power.

The instructions on the camera do not go passed the camera itself.

Interestingly enough, neither do their videos, which apparently is a common theme for rear view camera manufacturers. I do find a lot of other How-To videos of people doing similar things. Many skip over how they connect wires though, and many do things differently, thus why I thought I'd ask here then.

Avis wrote:I've wired up a few towbar and lighting sockets on cars, the options are as far as I'm concerned.

1) Scotch locks, plastic crimps that tap into an existing cable, I don't like these personally, they are fine for a temporary join and I've never had one fail tho that might be because I don't trust them so replace them soon after.
What's the downside of this method? They come apart? Connection gets worse / hot?
Avis wrote: 2) Strip the cable back slightly and solder onto it then tape it off (moisture is possible but if you're getting that much water in your car get a boat, a car shouldn't get that wet inside to be a real problem so long as the wiring is behind the trim.
This method could be tricky, but not impossible. I dont have a garage and placing a car near an electrical outlet to get a solder iron near it - is that tricky part... And it's winter everywhere here

So how much will I screw myself if I go with option 1?

Avis wrote: 3) disconnect the wire from the light cluster itself, solder or crimp an extra cable from there, this way is far neater than the above but more of a faff on.

4) get a set of connectors to make your own wiring harness/loom, if the car already has a modular wiring loom great get the male and female put the spur wiring from that and plug it back in, but even for common cars short of rummaging round a scrapyard finding the right connectors can be a pain in the teladi.
I think these two options a bit outside of my level, if I attempt it by myself.

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Post by UniTrader » Sat, 23. Dec 17, 03:16

i think option 4 is the best choice because you can prepare it in your home where you have space to work in.. if you dont want to make the whole connector maybe there is already a ready-made 10-20 cm extension cable for your back light connectors where you can add your additional wires an then simply plug it in between the back lights and the connector for them. Also has the advantage that you cannot break anything in your Car Wirking accidently this way.
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Post by Avis » Sat, 23. Dec 17, 18:27

fiksal wrote:...
The scotch locks are not really intended as a permanent connection (IMHO), one of the problems is with how they crimp on, they can damage the original wire, once removed they also leave a break in the insulation.
My main problem with them however it's little better than stripping the wire and wrapping a bit wire and taping, it might be simple but the continuity is questionable between the host wire and the joined.

I don't think you'd screw yourself doing the 1st option but I personally wouldn't rely on it, of course if it doesn't work out you always have the option of stripping and soldering into the wire anyway.

The soldering option isn't so bad, get a gas soldering iron they are fairly cheap.

At the end of the day a friend of mine who has done as many towbars as I have (for himself mainly) pretty much exclusively uses the bundle scotch lock boxes (it's a series of scotch locks in a block for keeping the job neat), and when he has had problems he's just fiddled with the scotch lock until it works, but as I said not my preferred method I prefer to do a more professional job and have the peace of mind it's done properly.

A lot of what I'm suggesting is for wiring a whole trailer board socket up,
For your use you just want the power from the reverse light by the sound of it, it might be just as easy to tap into the reverse light at the end of the wire where it goes into the light cluster (unless like the ford focus it's external) a scotch lock will probably be fine. if you damage the wire, solder it back together, no big deal it's not a brake light or anything that important)

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Post by Morkonan » Sat, 23. Dec 17, 22:26

fiksal wrote:The idea is to hook the camera up to rear, specifically, backup lights. This way when the car is in reverse, camera has power.

The instructions on the camera do not go passed the camera itself.

Interestingly enough, neither do their videos, which apparently is a common theme for rear view camera manufacturers. I do find a lot of other How-To videos of people doing similar things. Many skip over how they connect wires though, and many do things differently, thus why I thought I'd ask here then.

...
It shouldn't be drawing power from the backup lights. Instead, it should have a connection to them that detects voltage on that circuit, telling the camera that it should turn on. Well, that's the easy-way method I'd use to tell the camera to turn on. For that method, it'd need constant power, though. I suppose it could just power-on through the backup circuit, but that seems like a too brutish.

Do you know the make/model? Maybe we can pool our efforts and find some instructions for it.

How many connectors are on the device? ie:wires/plugs Can you see how many external connections are soldered to the board?

How does this device send its video? RF or hardwire? (Just curious)

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Post by Praefectus classis » Sat, 23. Dec 17, 22:53

Crimp or solder the joints first. If you want a tape that will keep the moisture out, self-amalgamating tape is the stuff to use. It sticks to itself and you stretch it to around 50% to get a good seal.
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