Tapping into signal wires

[mwebb]

do not poke a hole in the insulation , you will allow the green fuzzies to start forming inside of the harness and the wire will dissolve from the inside out
you will have a voltage drop that you will not know how to find

AES WAVE
sells probes , pin probes that will connect to leads for fluke and pico and other better quality test equipment .
like this connection to the signal pin of a Geo Metro Map Sensor

[Thymeclock]

Originally Posted by mwebb

do not poke a hole in the insulation , you will allow the green fuzzies to start forming inside of the harness and the wire will dissolve from the inside out
you will have a voltage drop that you will not know how to find

AES WAVE
sells probes , pin probes that will connect to leads for fluke and pico and other better quality test equipment .
like this connection to the signal pin of a Geo Metro Map Sensor

You mention "green fuzzies to start forming inside of the harness". If there is a harness, you can insert your probe into it without probing the insulation of the wire. But what if there is no harness near in the wire you want to probe? The pick probing technique I recommended it not at all using the fatness of a pin. The probe used is like that of a very slender needle. In fact you could probably actually use a fine needle and attach an alligator clip to it to get a reading. The "hole" made in the wire is so miniscule as not to cause a problem of corrosion or a grounding hazard.

BTW, I said "heftier" than a pin - but by that I mean stronger, not heavier or fatter.

[t vago]

You can use RTV to seal up any holes made in the wiring insulation. That, or F-4 tape should suffice. If possible, though, heatshrink tubing is preferred over either of these solutions.

My personal preference is to strip off the insulation from the signal wire in question, solder the other wire to it, then seal up the stripped part. Usually, I can get the splice near a wiring connector, which means I can take the wire's pin out of the connector and use a section of heatshrink.

[Thymeclock]

Originally Posted by t vago

You can use RTV to seal up any holes made in the wiring insulation. That, or F-4 tape should suffice. If possible, though, heatshrink tubing is preferred over either of these solutions.

Since the "hole" is smaller than a pin-prick it is usually unnecessary. Often the insulation itself is resilient enough to virtually close off the needle hole.

My personal preference is to strip off the insulation from the signal wire in question, solder the other wire to it, then seal up the stripped part. Usually, I can get the splice near a wiring connector, which means I can take the wire's pin out of the connector and use a section of heatshrink.

That's the situation if you want to tap into the wire. I've found that the 3-M type taps are usually OK if the wire is in the interior of the car. However if the wire is under the hood and exposed to the elements I have found the taps to be unreliable. Then doing a strip & solder as you suggested and using silicone sealant is the best way to go.

[t vago]

Originally Posted by Thymeclock

Since the "hole" is smaller than a pin-prick it is usually unnecessary. Often the insulation itself is resilient enough to virtually close off the needle hole.

Why take chances? Besides, I had a power wire leading to the left front foglamp on my truck go corrode out and fail because of a pinprick in the insulation.

Originally Posted by Thymeclock

That's the situation if you want to tap into the wire. I've found that the 3-M type taps are usually OK if the wire is in the interior of the car. However if the wire is under the hood and exposed to the elements I have found the taps to be unreliable. Then doing a strip & solder as you suggested and using silicone sealant is the best way to go.

I would never use wire taps. In fact, just thinking about using wire taps gives me one of them full-body shivers...

[some_other_dave]

I talked to an EE friend of mine about the taps. His opinion was that for something that is out of the weather in the interior of the car, a good-quality wire tap is a perfectly fine way of tapping into a signal wire.

I will admit that the thought of using them still doesn't make me very happy, though.

-soD

[Thymeclock]

Originally Posted by some_other_dave

I talked to an EE friend of mine about the taps. His opinion was that for something that is out of the weather in the interior of the car, a good-quality wire tap is a perfectly fine way of tapping into a signal wire.

I will admit that the thought of using them still doesn't make me very happy, though.

-soD

Good advice. I also heard it from an EE friend of mine, and he was correct. Anything that is in the outdoor elements of weather (read: under the hood) needs waterproofing; most interior applications don't.

I don't like crimp connectors for use in wire joining either. Between possible loosening and potential for corrosion, I avoid using them.