Spent 6 hours chasing a phantom voltage drop on a G1000 install

It was a simple LRU swap on a Cessna 182, but the new unit kept throwing a power fault. My meter showed 28 volts at the connector pin, but the avionics bay was a mess of old splices. The real issue was a corroded ground strap under the panel that only showed up under load. Has anyone else had a ground path hide that well?

3 comments

3 Comments

reese1772mo ago

Man, chasing those ghost grounds is the worst. I had one on an old Bonanza where the ground path went through the airframe itself, looked perfect until you put a real load on it. Took forever to find because the voltage drop only showed up when the autopilot servo kicked in. Makes you want to just run a whole new ground wire to the battery every time.

johns182mo ago

Tell me about it, I've spent more time chasing voltage drops than I care to admit. It's always the thing you assume is solid that bites you. Makes a guy feel REAL smart when the fix is just running one new wire.

margaret_nelson15d ago

Actually, it's not really a voltage drop, it's a voltage potential difference through the ground path that you're chasing. Voltage drops happen in the hot side, not the ground. The real issue is that the ground wire is carrying current back to the battery, and if there's resistance in that path, the voltage at the load drops because it can't get enough current. Common mistake, I made it myself for years lol. Also worth noting that airframe grounds in old Bonanzas are usually great if the bonding straps are clean and tight, but corrosion at the lap joints is what kills you. Took me way too long to learn that one.