Hello vintage mac mini user:
While working on my Mac Mini (2010), I accidentally pulled the wires out of two of the three 2-pin JST connectors that lead to thermal sensors for the hard drive(s) or optical drive(s) (depending on the Mac Mini model you have). Instead of the connector properly disconnecting from the motherboard, the connector stayed fastened to the board, but the wires were accidentally pulled out of the JST housing. The JST Connector case or package remained stuck on the logic board, only the wires came loose.
The connector itself is fragile—the thin layer of plastic that holds the wires in place is soft and can easily break with too much force. To make things worse, both wires were black, so it wasn’t immediately clear how to reconnect them correctly. As a result, the Mac Mini’s fan started running at full speed, a common symptom of thermal sensors not working properly. I didn't know which wire went where. As you can see in the lower framed image, there are two copper pins that the wires slide into, the wires that I accidentally pulled out through a mix of carelessness, clumsiness or connector age that made the plastic too soft.
The Problem:
When disconnecting the 2-pin JST connector, both wires came out of the plastic housing. With no color coding on the wires or any polarity markings on the motherboard, it wasn’t clear how to reconnect the wires. Although there was continuity from the motherboard to the wires, the fan continued running at full speed—a telltale sign that the thermal sensor wasn’t functioning, possibly due to an incorrect wiring connection (wrong polarity).The Solution:
Step 1: Trial and Error
Since this 2-pin JST connector was powering low-voltage thermal sensors, I decided to try a simple trial-and-error method to fix the issue:- I carefully reinserted the wires back into the JST connector housing (which remained attached to the logic board).
- After powering on the Mac Mini, I checked the fan's speed to see if the thermal sensors were working correctly.
- If the fan continued to run at full speed, I swapped the wire positions in the JST housing and tested again (see image below)
Step 2: Verifying the Fix
After a couple of attempts, the fan no longer ran at full speed, it as otherwise always starting up correctly with a chime and flashing question mark (two new SSDs in place). This indicated that the thermal sensor was functioning properly, with correct wire placement and polarity.Conclusion:
If you face the same issue with a 2-pin JST connector and find the fan running at full speed, don’t panic. A trial-and-error method can help you find the correct polarity for the wires, as long as the component is low power (like a thermal sensor). This approach solved my problem and restored normal fan operation in my Mac Mini.Always be careful when handling delicate connectors like these, especially in older machines, to avoid accidental disconnections.
Cheers!