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I want to do some electrical mods like adding a push/pull switch to my truck' tailgate to wire into my door ajar light to let me know if it is open along with splicing an electrical tailgate lock into the door auto lock mechanisms.

To do this I need to test for which wires are active during these certain things. I do not have a lot of experience with electrical.

Do I need a full multimeter with piercing probes, or is it enough to get a non-contact low voltage test light to test the individual wires in the harness for when the lock is pressed etc?

Gab
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  • I suppose it depends on if you want to know the voltage on the line. – DucatiKiller Mar 08 '16 at 02:03
  • It depends, i don't know if the other wires have power when the car is off. So if I see none of have power, except one when pushing the lock button, i suppose that should do it. The problem becomes when the other wires in the harness have power regardless of the car being off...then it would be hard to know which wire is wired to certain things. Im not sure.. – Gab Mar 08 '16 at 02:06
  • You can have power and low voltage resulting in issues operating various devices that require 12v – DucatiKiller Mar 08 '16 at 02:35
  • What is a non-contact low voltage test light ? I never heard about this, an the only tools I can think of are more expensive than a simple multimeter. Btw: If you don't have piecing probes, simple needles might help. – sweber Mar 08 '16 at 07:02
  • @sweber I think it means a probe like the ones used to detect the phase by electricians... but for lower voltages – Erik vanDoren Mar 08 '16 at 14:20
  • @ErikvanDoren I agree, but the traditional ones work with higher voltage (>90V) only and are NOT contactless. Those which are contactless also work with higher voltages, and AC only. The 12 or 24V are too low, and DC. – sweber Mar 08 '16 at 14:33
  • @sweber, there are contactless probes that measure both AC/DC, some can measure low voltages... maybe he is familiar witrh those, who knows, they arent cheap so... That they might or not be useful in car repair thats a different discussion – Erik vanDoren Mar 08 '16 at 14:54
  • @ErikvanDoren It's not a discussion of if they are useful. I'm just curious about those, as I have never heard about low voltage DC contactless probes... – sweber Mar 08 '16 at 17:39
  • @sweber what i meant by low voltage non contact light are the klein ncvt 3 for example – Gab Mar 08 '16 at 18:49
  • @ErikvanDoren klein ncvt3 for example, if something like that non-contact pen would be enough or do i need a multimeter? Do i really need to know what the voltage is or if there is just power – Gab Mar 08 '16 at 18:50
  • From the website of this klein ncvt3: Provides non-contact detection of AC voltage. Also the other contactless products from that company work with AC only. but the truck uses DC . – sweber Mar 08 '16 at 19:14
  • @Gab, not that one wont do, as mentioned already. It's not your electrician "pen type", they are probes that cost a pretty penny. There are Hall sensors that can be rigged up to a multimeter (sometimes a system used to check solar panels fyi), that might cost less than commercial probes if you dont count the fiddling time and looking for a suitable one as most are a ring and you need a V. But that, I think, you'll have to discuss in electronics SE. Again, if you read the answer you got you can see you don't even need it – Erik vanDoren Mar 08 '16 at 19:37
  • @Gab, from what i understand from your comments you just want to "blindly" catch a wire to splice-in, basing your decision of which wire purely on "I push this button - there's current on this wire". In some simple cases maybe it would work but most of the time you are asking for troubles doing it that way. – Erik vanDoren Mar 08 '16 at 19:46

1 Answers1

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This is quite easy, but you need to do yourself a favor and get a factory wiring diagram. It will save you hours of frustration and confusion. The factory wiring diagrams will tell you exactly when the circuits are active and when they aren't. On top of that they will tell you the colors and sometimes the current flow.

You really don't want to hook up a tail light to a fan circuit (Personal experience) =P

Once you have that, you'll need some thin wire probes or insulation piercing probes. They come with the Power Probe 3, and fluke also sells them. A decent multi-meter should help you track down the wires you want to use. If you decide that you want to use your own method to pierce the wires, just remember to wrap them in high temp electrical tape. When insulation gets compromised the entire wire inside it can corrode. It's a real pain to try and figure that out.

If you want to try to sort this out the oldschool way you can use the multi-meter, probes, and a test light. Essentially what you would do is attach your test light or multi-meter to to ground, activate the circuit and test each wire individually. BUT I don't recommend doing this. As I said before, if you put a lock mechanism on a fan circuit that might intermittently kick on, you'll have some serious issues. You could possibly even put it on an EVAP circuit, which would probably mess with the EVAP without realizing it and every time you put gas in your car, your tailgate would drop. I would get wiring diagrams, there are so many wires in a vehicles it's really hard to do it the oldschool way.

http://www.eautorepair.net/ That website carries a lot of factory wiring diagrams.

I hope I answered your question!

cloudnyn3
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  • Very informative, from here all I really am curious about now is whether something like the klein ncvt3 non contact voltage tester would suffice or would i need a multimeter that shows me voltage amounts? – Gab Mar 08 '16 at 18:56
  • Klein ncvt3 will not measure that current, see comments to your question. And you need to know the voltage per se for what you are doing. – Erik vanDoren Mar 08 '16 at 19:41
  • @ErikvanDoren ok thx, I was going to blindly catch a wire to splice in. What would you recommend otherwise? Should a shell out a few hundred and buy a multimeter? – Gab Mar 08 '16 at 20:16
  • @Gab, plenty of inexpensive multimeters around, a few bucks not hundreds, something like a Jameco BenchPro 1562 or comparable will be enough for your needs and its like 10$, a few bucks more will get u one that has a continuity beeper if you dont want to bother looking at the screen. Beside that, the answer above told you what to do. – Erik vanDoren Mar 08 '16 at 20:28
  • @ErikvanDoren awesome thx guys – Gab Mar 08 '16 at 20:33
  • I personally use a power probe 3 all the time. Best money I ever spent on a tool. – Ben Mar 08 '16 at 21:58