How to Use a Multimeter to Test Voltage on Sierra Wireless Airlink RV55 Connectors

If you're about to deploy a Sierra Wireless AirLink RV55 or any other Sierra Wireless device, this checklist is for you. I've been a field deployment tech for seven years, and I've personally documented 14 significant install mistakes, totaling roughly $12,000 in wasted budget. Enough to know where the real failures happen.

It took me three years and roughly 40 site visits to understand that the most expensive thing in an IoT deployment isn't the hardware. It's the second trip. A dead on arrival gateway is usually not dead at all—it's not getting the right voltage at the power jack. In September 2022, I cost my company about $3,200 by plugging an RV55 into a connector I had rewired myself. A multimeter reading would have caught it in 10 seconds. I didn't run one.

So now I run this checklist before every install. It's the one I created after the third avoidable power issue in Q4 2024, and it covers how to use a multimeter to test voltage on the connectors that feed the device. It's not theoretical. It's a checklist.

When This Checklist Helps

Use this before a new install, after any field repair, or when someone hands you a perfectly good power harness from the back of a vehicle. It also applies if you're troubleshooting intermittent reboots on a Sierra Wireless device. If you have a hard deployment deadline at the end of the day, a 10-minute voltage check is the cheapest certainty you can buy. This isn't about being paranoid. It's about not missing a slot because of a bad crimp.

The 6-Step Voltage Check

Step 1: Confirm the power spec and pinout for your exact model

Don't trust my memory, and honestly don't trust a YouTube comment. Check the label on the RV55 or the product documentation on sierrawireless.com. Most of the Sierra Wireless AirLink devices I've handled—certainly the RV55—accept DC input in the 9-36 V DC range, but you need to verify the exact range and polarity for your unit before you probe anything. Verify means put the meter on it. I do not mean glance at the label and hope.

The key connectors to inspect are the DC power connector on the supply, the connector at the end of the harness, and the jack on the gateway itself. On the RV55, the jack is usually marked PWR or DC IN. If it's not marked, find it in the hardware guide.

According to the RV55 hardware guide, the label on the unit lists the input voltage range and pinout. Use that label. It beats any blog post, including this one.

Step 2: How to use a multimeter to test voltage—the setting

This is where people overthink it. Turn the dial to the DC voltage setting. On most meters that's the V with a straight line above it. AC is the V with a wavy line. If your meter is not auto-ranging, choose the next range above your expected voltage. For a 12V system, 20V works. For a 24V system, 200V works.

Before you trust any reading, touch the two probes together. You should see zero or close to it. If you don't, check the meter battery and the leads. I've wasted an afternoon chasing a fault that turned out to be a broken probe wire. That's a pretty embarrassing way to learn.

Step 3: Test the power source at the output connector

Put the red probe on the positive pin and the black probe on the negative pin of the source connector. The display should show a positive voltage. If it shows a negative number, your probe leads are swapped or the connector is reversed. Either way, that's useful information. Fix it now, not after the gateway is mounted.

Step 4: Test at the device-side connector, not just at the source

This is the step most people skip. A power supply can read fine at the output, but the voltage that arrives at the RV55 jack can be much lower after a long cable run or a corroded splice.

Connect the harness to the power source and put your meter probes on the connector that plugs into the gateway. If the voltage here is noticeably lower than at the source, you have a voltage drop problem. Fix the cable, or use a larger gauge, before you connect the device.

Step 5: Test under load if you can

An open-circuit reading can look fine and still collapse when the modem starts drawing current. If you can safely put your meter probes on the power pins while the device boots—using a breakout cable or alligator clips—do it. A big dip below spec is a red flag.

If you can't load-test, at least do a quick sanity check with a known-good device before you blame the gateway.

Step 6: Inspect the jack and connector before powering up

Do not open the gateway to poke around on the circuit board. That's how you void the warranty and turn a $500 problem into an $800 problem. Instead, check the jack itself for loose pins, bent sockets, or corrosion. If the plug fits loosely, the device can lose power during vibration—a classic intermittent problem in vehicle installs.

Your goal is to know that the voltage you measured on the harness is actually reaching the device. If the connector is clean and snug, and the voltage readout is in spec, you're safe to power up.

Other Connectors Worth Checking

The voltage check matters for power, but the RV55 also has RF connectors and a serial connector. Don't assume they're tight just because they came in a box. A loose RF connector can cause signal drop, and a loose serial connector can cause configuration headaches. The same habit—look at the connector before you screw it in—applies.

If you're using an extension cable on the antenna ports, check the connectors for stripped threads. I once picked up a brand-new RV55 with a damaged antenna connector because someone forced a mismatched SMA pin in. That's not a voltage issue, but it is a connector issue, and it will eat your deployment window just as fast.

Three Mistakes That Cost Me Real Money

I went back and forth between buying a cheap continuity tester and a proper multimeter for two weeks. The continuity tester gave me a beep. The multimeter gave me a number. When you're working with DC power and a deadline, a number is worth the extra cost. I've never regretted that purchase.

What most people don't realize is that a surprising number of defective Sierra Wireless devices returned for no power bench-test fine. The original install had reversed polarity, a bad splice, or a worn jack. The return is a symptom, not the problem.

• Reversed polarity – A negative reading at the connector is easier to fix before you connect than after.
• Voltage drop on a long cable – The supply reads fine, but the RV55 never gets enough.
• Bad meter fuse – A blown fuse in your meter can make a good gateway look defective.

Bottom Line

Testing voltage on Sierra Wireless devices isn't advanced electrical work. It's a ten-minute habit that separates smooth deployments from emergency truck rolls. If you're facing a hard deadline, remember that a multimeter check buys certainty—and when a site visit is on the line, certainty is worth more than the rush fee you'd pay to fix a device after the fact.

Keep the checklist simple. Confirm your pinout. Set the meter to DC volts. Test at the source. Test at the connector. Test under load. Inspect the jack. Then, and only then, plug in the RV55.