Wire Tap - Don't use them!

I know a lot of people have a need to join an extra wire into an existing circuit and very often use a Wire Tap device.

Having worked in the auto elec world may I suggest if you are confronted with this task do not use this method as

1. the crushing action often breaks some strands of your original wire
2. unless done absolutely perfectly you can finish up with a high resistance joint
3. the devices are not waterproof making the joint subject to corrosion and ultimate failure.

Here is what these devices look like (although some suppliers have variations on these)


Here is my technique
The original wire plus the tap



Peel back some of the insulation without cutting the original wire. Strip insulation from tap wire.


Twist the tap wire around the original wire


Finally, solder the wire joint and wrap it in plastic tape (if you have some, use rubber vulcanising tape (Scotch 33 or similar) for a waterproof joint.

Happy to say I've never used one of those plastic things

I learnt a long time ago that these things are very unreliable.

I too make my taps the same as you do, with one exception I cut the wire I'm tapping into so I can use heat shrink instead of tape

I would prefer to use heat shrink instead of tape except for a bad experience I witnessed.

A workmate of mine cut a live wire in a Mitsubishi Diesel 4WD.

All seemed OK  except the engine would not run afterwards.

Apparently the ECU had some form of intrusion detection.

The vehicle had to be taken to Mitsubishi dealer on a tilt tray to have it's "brain" reset. ($400 plus tilt tray cost - boss was not amused   )

I'm not suggesting this would always be the case but I won't take the risk after seeing the consequence in this case.

Never come across that one! However there are so many things that can screw with a vehicle's ECU it always pays to disconnect the battery first.

Anyway most of the stuff I do is usually simple things like trailer wiring, Spotlights, accessory plugs and the like.

I also prefer the strip and solder connection as well.  The only difference is I also use a small pick to open the continious wire into a small oval and feed the connecting wire through it then twist and solder, I found it gives that extra bit of physical bonding and is a slightly less bulky join.  

If it is for a joint that has to be waterproof then a dab of Liquid Elecrical Tape from Jaycar is pretty good.

Howdy MM

We were installing mainly two way radios and mobile phone cradles.

At the time, battery disconnection meant resetting the am/fm radio and the clock. I know his can be done much easier nowadays.

The boss did not want time wasted on these matters and encouraged the work to be done live.

Having power to one part of the "brain box" and disconnecting (cutting another circuit) obviously was too much for the vehicle to cope with.

What actually happened was the power to the diesel fuel pump was shut off.

What really surprised me was when Mitsubishi dealer insisted we bring the vehicle to him, not him visit us.

I hope things have changed since that time and that RAC service vans can effect a repair.

I don't know if this is relevant but the vehicle in question was a Mitsubishi 4WD 2007 (I'm pretty sure)

barry_mcki wrote:I also prefer the strip and solder connection as well.  The only difference is I also use a small pick to open the continious wire into a small oval and feed the connecting wire through it then twist and solder, I found it gives that extra bit of physical bonding and is a slightly less bulky join.  

If it is for a joint that has to be waterproof then a dab of Liquid Elecrical Tape from Jaycar is pretty good.

Howdy Barry,

I haven't used this product but it sounds like a very good solution to me.

Wouldn't use it on every join, but there are times where you need insulation and nothing else will do.

They also sell Heatshrink Tape but I find it a little too wide (25mm) and a bit bulky, but good for larger jobs.

Excellent post, Dave. 
It's always nice to share knowledge that may prevent others suffering on the side of the road.

Excellent advice

I couldn't agree more. As a former fleet mechanic I used to hate having to sort out electrical issues caused by poor connections when vehicles were supplied with accessories connected with these clips. They cost hours of rework later on.

ive seen these used alot. Especially when i rewired a race car not to long ago. I only ever use good old solder and heat shrink.

When I got some Admore LED kits for my Givi cases they came with a couple of Posi-Taps.  I didn't use them as I thought they would be the same as the fore mentioned wire taps.

I've recently looked at them again, and I think they might actually be worth considering, would be interested to hear from anyone who has used them.  

They look like this - come in a variety of sizes, and seem to overcome all the issues of the old crimp style taps:

Howdy Barry

My main reservation with wire taps generally is the potential to break some strands of the wire. Bandit wiring is already incredibly thin and any loss of wire cross sectional area would only make matters worse in any circuits carrying a bit of current.

The headlights are probably the worst circuit where I measured 1.8volt drop between battery and bulb. Fitting of relays and heavy cable overcame this problem.

I guess for other than headlights the loss of a wire strand would not be that much if an issue.

I think I would use them for a field repair but probably replace them with a soldered joint once I returned home.

+1 for the Posi-Taps. I too would only solder rather than use the crappy wire splicers. After several Hyper-light brake light LED installs I bought a pack of Posi's for other applications. They work fantastic and can be installed in tight places.