Need Electrical Help

[Doug Rohrer]

I wanted to repaint the stock Van's steam gauge panel in my -9A, which had been spray-canned by the builder. I removed an unbelievable amount of screws and got the panel out for powder coating. The instruments, switches and gauges were supported by tape and zip ties while the panel was out of the plane. After reinstallation of the panel, I discovered the ammeter swings to full discharge (>40 amps) when the master switch is turned on. Even with all electrical loads turned off, the amp gauge pegs. Everything seems to work normally (avionics, lights, flaps, etc.), and there is no smoke or sparks. You can hear the master relay snap closed when the switch is turned on. The engine starts and runs normally. No change in ammeter reading with the engine running and alternator on line.

I did swap out the master switch (Cessna) for a new one of the same type (old one was faded). I was careful to reconnect the wires to the terminals just like the old one, but I could have possibly swapped a wire. I don't see how the system would keep working if I swapped wires. Battery is a PC680 in good shape and fully charged.

I don't see how I can have this large of a load and not have breakers tripping or smoke/sparks coming out from under the panel.

Anybody have any suggestions what to check next?

Thanks.

[Jesse]

With problems like this I always go to the sensor first. Find your ammeter shunt and see if a wire has come loose or is shorting.

If there is no voltage change when the amps go crazy, then you almost certainly have an ammeter problem, not an electrical system problem.

[rwarre]

I fussed with Van's ammeter gauge for almost six months before I got the wires connected properly. I have a second Van's ammeter if you want to try that. It has been sitting on a shelf and I would be happy if it was put to good use.

[Doug Rohrer]

In the interests of resolving this thread, I found the problem was a broken wire connection at the back of the ammeter. My gauges were obviously wired up with the panel on a bench by the builder, and he used the shortest possible amount of wire to connect between the gauges. Any time I have to replace a gauge, it is a nightmare getting access to the back of the unit, because there is not enough wire to turn them around and work through the hole. After spicing in an extension lead with a good crimped terminal, I made a new connection and all is right with the world again.

Note to self if I ever build a panel from scratch: leave service loops of wire for future connections.