JST Connector Types and Voltage Testing: A 6-Step Field Checklist

Ever had a connector sit on your bench because you can't tell a JST PH from a JST XH? Or ordered a 'JST 2-pin' and it didn't fit? This checklist is for you. In my role coordinating urgent connector orders for electronics manufacturers, I've handled 200+ rush orders in three years. Last quarter alone, we processed 47 rush orders with 95% on-time delivery. The 5% that slipped were almost always connector identification errors. This is the same process I use when I don't have time to guess.

It took me about three years and too many wrong orders to realize that pitch measurement beats visual matching. If that sounds basic, it kinda is—but it's also the step that gets skipped. Here are six checks to get you from unknown connector to working assembly.

Step 1: Measure the pitch first

Most JST 2-pin connector types look identical in photos. The pitch is the center-to-center distance between the two pins. That number is the fastest way to tell them apart.

• SH: 1.0 mm
• ZH: 1.5 mm
• PH: 2.0 mm
• XH: 2.5 mm
• VH: 3.96 mm

Use calipers. If you don't have calipers, lay the connector on a metric ruler and count carefully. I do not mean the outside width of the housing. I mean the distance from pin center to pin center. A 2-pin PH is often mistaken for XH because both are small and white. Measuring solves that in five seconds.

Most people try to visually match a photo. That works on the first try maybe 70% of the time. The other 30% costs you a week. Measuring is faster in the long run.

Step 2: Count pins and orientation

This sounds obvious, but pin count is where I've seen real delays. A 2-pin connector is usually positive and negative. A 3-pin connector often includes a thermistor or signal line. A 4-pin or 6-pin version can be used for battery balance leads, LEDs, or data.

In a rush, it's tempting to stop after confirming the 2-pin count. Don't. Check the orientation of the locking face. Some JST housings are top-entry, some side-entry. If you push the connector and it won't seat, the orientation is wrong.

Pin orientation matters just as much. In a 2-pin JST connector, the latch position tells you which side is up. If your cable assembly is routed tightly, a 180-degree connector can be the difference between a clean build and a broken strain relief.

Step 3: Verify the locking mechanism

JST connectors are not all friction-fit. PH has a small latch on the side. XH has a tab on top. SH has a tiny lock that's easy to break. ZH has a smaller latch than PH. VH uses a stronger lock for higher-current applications.

When you're comparing a sample to a datasheet, check the lock first. A connector that visually fits but doesn't click will vibrate loose. I've seen assemblies fail a final test because someone used the wrong 2-pin housing that happened to slide in.

The locking hook can also break if you insert the connector upside down. If the connector doesn't snap in with a light push, stop. Forcing it will damage the terminal and create an intermittent problem later.

Step 4: Check wire gauge and current rating

According to JST Mfg's catalog (jst-mfg.com), PH connectors are rated 2 A AC/DC and accept 28–26 AWG wire. VH is in a different class, with a higher current rating and 3.96 mm pitch. XH falls between them.

Don't choose a connector by pitch alone. If your load draws 3 A, a PH connector is not the right call, even if it fits mechanically. This is one of those things that doesn't fail at the bench. It fails in the field, three weeks later.

When in doubt, choose the next pitch size up and verify the exact terminal part number. A quick check now is always faster than a re-order cycle later.

Step 5: How to use a voltage tester on a JST connector

Here's how to use a voltage tester to confirm what you're dealing with before you connect anything.

1. Set the tester to DC voltage. For most JST battery connections, the 20 V range works well.
2. Identify the negative pin. In a 2-pin JST battery connector, it's usually the black wire. Put the black probe on that pin.
3. Put the red probe on the positive pin. For a battery pack labeled 7.4 V, you should see around 8.4 V when fully charged and around 7.4 V at rest. A reading like 7.1 V under load is not a fault by itself.
4. If you get a negative reading, you have the probes reversed or the pin polarity is opposite. That's a useful warning before you plug in a device.

For example, a platinum blood pressure monitor I repaired last year used a PH 2.0 2-pin connector for its battery. The label said 6 V. My first voltage test read 0 V because the battery connector pin, not the battery, had a broken crimp. A quick continuity check on the pins saved me from condemning a good battery.

Never poke through wire insulation with your tester probe if you can avoid it. Use backprobes or test at the exposed terminal. Damaged wire insulation creates intermittent shorts, which are worse than the problem you're trying to find.

Step 6: Verify the JST to JR adapter before wiring

A JST to JR adapter is common in RC and embedded projects. It lets you take power from a JST battery connector and feed it to a JR-style receiver connector. It's not a 'same pins, same wires' situation. The plug geometry is different, and pin order varies by manufacturer.

Before you use an adapter, test it. Put your voltage tester on the JR connector side and confirm positive goes to positive. I've seen receivers smoke because the adapter's pin order was reversed. The adapter may cost a few dollars; a replacement receiver costs more.

Even after I ordered the right JST to JR adapters for an urgent batch, I kept second-guessing. What if the factory swapped the pin order? The two days until delivery were stressful. I didn't relax until the first unit passed the continuity test.

Common mistakes to avoid

Don't order by the name 'JST 2-pin' alone. There are many JST 2-pin connector types, and the name doesn't include pitch, lock style, or current rating.

Don't trust housing color. White, black, red, and clear are all common. Color is not a spec.

Don't force a connector. If it doesn't snap in, it's the wrong type. Forcing it can warp the terminal and create intermittent contact.

Don't forget to test polarity on adapters. One 30-second check prevents a board fault that can cost hours.

Quick recap: measure pitch, count pins, check the lock, match current rating, test voltage, and verify adapters. That process cuts my identification time from minutes to under a minute.

Specs as of January 2025. Verify current JST datasheets before production runs.