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Piwoslaw 12-08-2010 09:17 AM

Tapping into signal wires
 
What is the best (ie safest) way to tap into a signal wire? There are a few sensors that I'd like to monitor, the "signal" is usually just the voltage (eg 0V=open, 5V=closed, etc). Since taking the plug or socket apart is too hard (if at all possible), I have to somehow get into the wires. I can see three options:
  1. Cut the wire, then solder it back together with a third wire for monitoring,
  2. Same as above, but without cutting, only stripping some of the insulation off,
  3. Insert a metal sewing needle through the insulation and solder the monitor wire to the needle.
Since I want to monitor the signal only for a short period of time, I would like to be as non-invasive as possible. Options #1 and #2 may lead to problems with corrosion in the future, so is #3 the best?

Daox 12-08-2010 09:26 AM

If its temporary, I'd do #3. Put some electrical tape over it after you're done just to be safe.

JasonG 12-08-2010 09:27 AM

I'm not sure if they are available in Poland, but here the auto parts stores carry splice taps.
they clamp on to the wire and provide a 3rd port for a new wire.
when removed the insulation only has a small nick like your needle idea.

example: BWD CT617A - Terminal | O'Reilly Auto Parts

dcb 12-08-2010 09:50 AM

solder a lead to the pin, then stick it into the wire. Wipe a little silicone sealant over the hole(s) when you take the pin out if so inclined to restrict further oxidation.

RobertSmalls 12-08-2010 07:00 PM

If you can get at the ends of your wire harnesses (e.g. where they enter the ECU), you can get a narrow probe in there without piercing the insulation.

Thymeclock 12-08-2010 11:07 PM

Apparently what you are seeking is a way to read the voltage of the wires by piercing but not cutting the insulation. It's called pick probing. You will need a few, very sharp dental instruments that can pierce through the insulation of the wire just enough to make contact with the wire. The handle end of the instrument will be attached by an alligator clip to the meter you are using. When you remove your pick, the pin prick in the insulation will be so slight as to need no remediation to the wire or its insulation

(I've only been using this technique for 40 years. If you find it useful a 'thank you' would be appreciated.) ;)

Piwoslaw 12-09-2010 02:58 AM

Quote:

Originally Posted by RobertSmalls (Post 208665)
If you can get at the ends of your wire harnesses (e.g. where they enter the ECU), you can get a narrow probe in there without piercing the insulation.

That's the problem - where I could, I took the plug/socket apart and added a thin wire to the pin. But in many cases the harness is waterproofed and can't be taken apart without breaking something. I've tried, but too many layers of plastic and silicone.

Quote:

Originally Posted by Thymeclock (Post 208680)
You will need a few, very sharp dental instruments

Dental instruments (chill runs down spine)...

Quote:

Originally Posted by Thymeclock (Post 208680)
(I've only been using this technique for 40 years. If you find it useful a 'thank you' would be appreciated.) ;)

Thanks to everyone:thumbup:

dvldrmmr 12-11-2010 08:03 PM

you could get another connector, and solder pins on the end to fit into the original connector, splicing off a wire as in #1. then when you're done, just unplug your "piggyback" setup, and plug the original connector back in. sort of a man-in-the-middle type setup, and no worries about corrosion/broken wires with method #3. just a thought.

Thymeclock 12-12-2010 12:31 AM

Quote:

Originally Posted by dvldrmmr (Post 209022)
you could get another connector, and solder pins on the end to fit into the original connector, splicing off a wire as in #1. then when you're done, just unplug your "piggyback" setup, and plug the original connector back in. sort of a man-in-the-middle type setup, and no worries about corrosion/broken wires with method #3. just a thought.

Method #3 will neither cause corrosion, nor broken wires. But you need something a bit heftier than a pin, and a sharp, fine dental instrument is just right for the job of pick probing.

gone-ot 12-12-2010 02:24 PM

+1 for method #3, the 'pin-thru-insulation.'

...and a single wrapping of self-vulcanizing tape seals everthing up tight.


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