Finding the best probe

Some of the criteria we will be using to judge a given probe are:

Does it attach to the circuit securely such that it will not lose contact during a test-drive or a harness wiggle test?
Is it quickly and conveniently attached to a given circuit?
How versatile is it when attaching to different size wires?
How much reach does it have to grab wires found in hard to reach places?
Can it be installed into small spaces?
How well does the probe hold up over time and use?

Four different test probes are shown in Figure 1. During the article, we will refer to them as Probes A, B, C and D for convenience sake. The caption underneath the photo lists the manufacturers of these probes, should you have an interest in learning more about any of the probes. Also, these are just an example of the probes available in today's aftermarket.

The same probes are shown with closer views of their connection jaws in Figure 2. You should refer to these two figures as you read through the following text.

Starting with Probe C, we see that the general shape of the probe is a "T" at the bottom. A banana plug connection is made on one side of the "T-bar" to connect your test lead. The round button below the "T" is depressed to withdraw the single needle back to allow the tested wire to be inserted into the V-block at the tip of the probe.

These probes are very quick and easy to install on a wire. The knife-like tip of the probe allows for an easy grab of a single wire, even if the chosen wire is buried within a large group of wires in a harness. Simply knife edge the probe into the harness above or below the chosen wire, push the needle retraction button and turn the probe to hook the wire as shown in Figure 3 I use these probes most often to make fast, one-time measurements.

These probes are not suitable for installation on test-drive testing nor on wiggle testing a circuit. They tend to lose their connection if manipulated harshly.

In addition, these probes' tips are small and not suitable for larger wires. They also tend to bend their V-block tips over time and abuse, causing the needle to miss the point of the V-block and making it difficult to get a good connection.

I consider these to be frequently used hardware items and keep a stock of them around. I just switch them out when they bend. They sometimes can be difficult to install in tight spaces because of the required twisting motion needed to hook the wire while your test lead is run in from the side. These probes come in lots of different colors for multichannel scopes.

Probe A has the same knife-type edge at the tip, however, it is a bit fatter. This makes it slightly more difficult to grab a wire in a bundle of wires than Probe C. However, it does accommodate larger wires, and I have yet to wear out one of these. These have a banana connection at the bottom that makes them more slender for probing in tight spots. They also have a greater reach.

These probes are installed on a wire by twisting the black portion while holding the green portion to retract both the needle and the needle shroud. This sometimes requires two hands, which might not fit into a tight spot.

However, because the shroud and needle move together, the connection is rock solid and suitable for test driving and aggressive wiggle testing. Probe A also comes in an even larger and longer version for large wire gauges up to about 12Ga.

Probe B is also a twist-to-install probe. In addition to that feature, these probes have a banana plug connection at the bottom. They are small enough for tight spaces, though they typically do require two-handed operation. They too have a shroud that helps hold the wire and needle connection tightly and are suitable for both test drives and wiggle tests.

You do have to retract the spring-loaded shroud by sliding the black portion back while grabbing the wire. The tip on these probes has a rounded point tip. In my experience, it is more difficult to get this tip into a bundle of wires than it is when using either Probe A or Probe C.

Probe D is a back-pinning probe used for momentary testing and is not suitable for test-driving or wiggle test. The pins are bendable, which make them easy to install at angles. These probes also have replaceable pins, so you can get long life out of them.

No matter which probe you chose to use with your diagnostic testing, there are other things you need to remember. One example is you must remember that whenever you pierce a wire, always cover the pierced hole with liquid electrical tape when finished. Failure to seal a hole will allow moisture in and will create a breeding ground for corrosion. If it is left open, a new problem will soon appear to replace the one you just repaired.

Jim Garrido of "Have Scanner Will Travel" is an on-site mobile diagnostics expert for hire. Jim services independent repair shops in central North Carolina. He also teaches diagnostic classes regionally for CARQUEST Technical Institute.