I've spent the last few years getting yelled at by engineers. Not just the ones I work with — also the ones who send me field returns and expect me to explain why their product failed.
I'm a quality compliance manager at a global interconnect company. Everything I sign off on goes into medical devices, vehicle electronics, or industrial equipment. I review a few hundred unique assemblies a year, and I've rejected roughly one in eight first deliveries in 2024. Most of the time, the underlying reason is the same thing that's hiding inside your "broken" blood pressure monitor.
So if you're here because you searched for blood pressure monitor symbols, or you found a loose Molex 150 connector on a board and wondered whether you could just re-crimp new pins — this one's for you.
The Symptom That Isn't What It Looks Like
Blood pressure monitors don't usually die. They develop quirks. You know the pattern:
- A heart icon that pulses forever but never locks in a reading
- An "E" or "Err" symbol sitting where the systolic number should be
- A battery icon insisting the device is charging, whether it's plugged in, unplugged, or contains no battery at all
The usual reaction is to blame the main board. Or the sensor. I've watched technicians replace both, reassemble the device, and see the same symbol return a week later. That's not random bad luck. That's a symptom masking a deeper problem — and most people stop one diagnosis too early.
The Connector in the Middle
Pop the board out. Turn it over. Between the pressure sensor and the main controller, you'll usually find a small board-to-board interconnect. In a lot of these monitors, it's a Molex connector. Sometimes a compact series like the Molex 150 connector family; sometimes a standard pitch header. Depends on the generation of the device.
Searching for Molex board to board connectors gives you datasheets with dimension drawings and electrical ratings. What the datasheets don't tell you — what only field returns teach you — is how much abuse these little parts endure. Temperature swings. Humidity. Vibration from the pump every time the cuff inflates. Not enough motion to break the connector, just enough to expose a weak crimp.
Because here's the secret: the connector body is rarely the failure point. The metal terminals are rarely the failure point. The failure is almost always a buried crimp — the place where the wire was squeezed into the terminal barrel in the factory, or at the workbench, never formed a proper bond.
That failure mode is invisible, intermittent, and perfectly designed to drive you crazy. It works when it's still. It fails when the board flexes, when the temperature changes, or when someone picks the device up and carries it to another room. Then the signal glitches for a fraction of a second, and the monitor shows a random symbol instead of a blood pressure number.
An Old Crimp Myth Worth Debunking
There's a belief out there that a crimp pin just needs to be "tight enough." That thinking is a leftover from an era of fat terminals, heavy wires, and tools that worked like vises. Today's miniature connectors don't tolerate that.
A crimp pin is a precision assembly. Too loose and the wire slides or makes intermittent contact. Too tight and the strands crush or fracture, creating a joint that measures fine when static but can't carry a signal under load. The sweet spot is defined by crimp height, strip length, and conductor brush — and it varies from terminal to terminal.
This is why the correct crimp tool for a Molex 150 connector or any similar series costs real money, and why the universal pliers out of a hardware store bin aren't an upgrade. They're a compromise. Sometimes a fatal one.
There's an industry standard for this, believe it or not. IPC/WHMA-A-620 exists precisely because these details matter. It defines what an acceptable crimp looks like, how to test pull-out force, and what counts as a defect. A lot of the parts I reject would fail that standard in seconds.
I've heard "it's within industry standard" from suppliers at least twice this year. Neither time was true.
The Cost of a "Sometimes" Connection
Let me make this concrete, because intermittent sounds harmless right up until you see the receipt.
In a Q1 2024 quality audit, a contract manufacturer shipped 8,000 crimped leads that failed my inspection. Under magnification, the crimp barrel showed hairline cracks — the signature of a worn die set they'd put off replacing. When I flagged it, they argued. "Within industry standard." We measured them. Technically at the edge of our spec. But edge-of-spec doesn't belong in a medical-grade assembly. We rejected the entire batch.
Even after making the call, I kept second-guessing. Did I just overreact? If they're at spec, am I going to be the one explaining a schedule slip to sales? It wasn't until the replacement batch came back perfectly formed that I stopped replaying it. In the end, their rework cost them about $22,000 and three weeks. More than five times whatever they'd saved by running a die set past its useful life.
That's the value-over-price math in action. A $200 savings on a crimp tool, or a $0.02 cheaper terminal, only looks good in a procurement spreadsheet. The moment a field failure happens, any savings evaporate — because the cost of service, rework, and reputation always dwarfs the component price difference. That's true for a patient-side blood pressure monitor and true for a 50,000-unit assembly order.
And in a blood pressure monitor, the cost of a "sometimes" connection isn't just time and money. It's trust. A device that shows nonsense symbols gets thrown in a drawer. A clinical device that does the same gets an incident report. Neither outcome is okay when the fix was genuinely simple.
How to Check With a 117 Multimeter
The good news is you don't need a lab to find a bad crimp. You need a meter that won't lie to you.
The Fluke 117 multimeter is the one I keep on my bench. It's not exotic or newest, but its low-impedance mode filters out the induced "ghost" voltages that make ordinary meters read healthy when the circuit is actually dead. In the world of intermittent connectors, that feature basically removes a whole category of confusing data.
Here's the test: put the meter in continuity mode. Clip one probe to the terminal on the connector side. Touch the other probe to the stripped wire at the far end. Then — here's the step everyone skips — gently pull on the wire while you watch the meter.
A good crimp stays connected through the pull. A bad crimp beeps, drops out, then beeps again. That exact pattern is the technical signature of the intermittent signals causing all those blood pressure monitor symbols.
If the crimp fails, don't squeeze the terminal with pliers to "tighten it up." That makes everything worse by crushing the barrel around already-damaged wire strands. Do it right:
If You Need to Re-Crimp, Do It Right
- Confirm the exact terminal part number for your connector. Not "a similar one." The exact one. Molex's documentation is freely available, and a distributor can often send a sample if you're unsure.
- Strip the wire to the length specified in the datasheet. Strip length is not a suggestion.
- Position the terminal in the correct die. For a Molex 150 connector, the tooling section of the product page lists the right applicator or hand tool.
- Crimp with one complete stroke of a ratchet tool. The ratchet won't release until the crimp reaches full height — that's the whole point of it.
- Pull-test the wire with firm force. If the terminal comes off or the wire pulls out, your process is wrong, not the parts.
If "how to crimp pins" is the question you came here with, those five steps are the whole answer. They're short — but each of them matters far more than people expect.
The Bottom Line
The weird symbols on a blood pressure monitor are a messenger. The real problem is usually a degraded signal path between boards — and more often than not, the degraded link is the crimp inside a tiny Molex connector.
Fix it by replacing the terminal with the right part, crimping it with the right tool, and verifying the continuity while pulling on the wire like you mean it.
That's the standard I hold our suppliers to. It's also why the 8,000 unlucky leads got rejected in Q1 2024.
This was accurate as of Q1 2025. Part numbers, connector series, and tooling change over time, so verify against current manufacturer documentation before ordering.
