Piercing And Probing Wires With The Least Damage Possible

Piercing And Probing Wires With The Least Damage Possible

The Hippocratic Oath states a doctor shall "do no harm." The technician's oath is the same, but we "do no harm" to a vehicle we are trying to diagnose or repair.


The Hippocratic Oath states a doctor shall “do no harm.” The technician’s oath is the same, but we “do no harm” to a vehicle we are trying to diagnose or repair.

This oath has become more difficult to follow as vehicles have become more complex. Probably one of the most controversial topics among technicians is the probing and piercing wires and connectors. Some technicians curse t-pins and piercing probes claiming they can damage a wiring harness. On the other end of the spectrum are technicians that have zero problems stuffing a blunt multimeter lead into a connector for an ECM.

Back in the day, a technician could carry out most electrical diagnostics with just a test light. Every voltage value was 12 volts, and the most sophisticated component might be the ignition module. Things have changed.Modern voltages can be three-, five- or 12-volts and they might have a pulse. These signals move a ton of information. The flickering of a test light or dancing of digits on a multimeter could be serial data to command a window down or just a faulty ground. Also, the slightest amount of green corrosion or high resistance can set codes.

Being able to capture a signal, voltage or glitch is critical to diagnosing many problems and codes on a vehicle.

Connecting a multimeter or scope to a circuit is sometimes very difficult. Making the connection in the least invasive way possible is critical to achieving a confirmed diagnosis.

T-pins and needle probes have been around for a long time. These can be inserted into the back of a connector to back probe the connection. The best way to use these is to slide the pin between the connector housing and weather pack grommet. If there is no grommet, you can slide the pin gently into the insulation. There is no guarantee of the contact being made between the pin and wire. Also, there is no way to know if the pin is damaging the terminal. But, back probing with a pin might be your only option. Specialty back probes will have a small diameter and create less leverage on the connector. Some back probes have a rounded spade profile that can be used on small diameter wires.

Piercing probes perforate the insulation of a wire with a needle. The needle can be spring loaded or screwed down into the wire. This type of connection might be the best option if a sensor is buried deep inside an engine or a connector is inaccessible.

One of the least invasive ways to connect to a circuit is a breakout. These can be attached inline or as a test point so that a scope or multimeter can measure the circuit. Some breakouts can be connector specific like for an oxygen sensor or OBDII connectors. Breakout test leads can mimic the male and female terminals in a connector.

Breakout leads can do the least amount of damage to the wiring and possibly the terminals, but they can also introduce a wild card into your diagnosis if you are not careful. In many cases, the connector is the source of an electrical problem. Disconnecting and reconnecting a connector might clear up a bad connection for a short time. This is why it is always a good idea inspect both sides of the connector when you first pull it apart.

Even if a doctor saves a life, there might be scars left behind by a scalpel. But, the sign of a good doctor is a less noticeable scar that heals. The same is true for wiring harnesses and technicians.

You May Also Like

Success Means Investing In More Than Equipment

Todd Baldridge measures success by how well his team benefits from being together.

When I sat down to speak with Todd Baldridge, owner of Buckeye Complete Auto Care in Columbus, OH, I was struck by his candor, his openness and his complete honesty about his shortcomings as a business owner.

The cover story in this March issue of ShopOwner is full of self-reflection and acceptance – but it isn’t a depressing story of what wasn’t. Baldridge is eager to look forward as well, to what CAN be. 

Were Things Better When They Were Simpler?  

Getting nostalgic about the good old days is easy, but many forget the struggles of the time.

Becoming Successful Often Means Investing in More Than Equipment

The cover story in this March issue of ShopOwner is full of self-reflection and acceptance – but it isn’t a depressing story of what wasn’t.

Would You Want To Work on 40 year Old Car?

Last month, Andrew Markel purchased a 1982 Chrysler New Yorker for $1,500.

Adapting To Enduring Expectations 

Where we once provided business and technical information in a monthly print magazine, we now have daily newsletters and on-call websites to help spread the message of quality service.

Other Posts

Misfire Codes P0300, P0301-P0312 and P0313+P0314

The only way to clear the code is to use a crankshaft position relearn with a scan tool.

Jump Starting an EV

If an EV with a full battery won’t start, here’s how you can get it up and running.

Diagnosing Misfires

What if there are no codes and a misfire is intermittent? This is where it gets complicated.

Using a Scope

Ignition coil and plug diagnostics.

Scope-diagnostics