Interesting find

[Murdoughnut]

Breaker on our Archer for the stall warning horn kept popping. Thankfully we have some super anal A&Ps in our club. Found the wiring all a mess and a section of wiring for the stall horn missing. Where was it you ask?

Caught up in the chain for the yoke

 

[Roger Roger]

Typical GA wiring

 

[knot4u]

Breaker on our Archer for the stall warning horn kept popping. Thankfully we have some super anal A&Ps in our club. Found the wiring all a mess and a section of wiring for the stall horn missing. Where was it you ask?

Caught up in the chain for the yoke

Are your super anal A/Ps going to fix the rest of the wiring? I understand they're probably working for free or dues but I'd assume they're flying the airplane also. Unfortunately that sort of thing is a solitary adventure (due to space) and it only gets worse as you progress. A hangar day to fix the wiring is probably just going to piss off the one person actually in there doing the work, although having one person around is good in case you get stuck and need someone to pull you out by your feet, check continuity on something you can't reach, and sometimes to drink some water and stare at the infernal contraption while you commiserate and wonder why you ever decided to do this to begin with.

 

[Murdoughnut]

Are your super anal A/Ps going to fix the rest of the wiring? I understand they're probably working for free or dues but I'd assume they're flying the airplane also. Unfortunately that sort of thing is a solitary adventure (due to space) and it only gets worse as you progress. A hangar day to fix the wiring is probably just going to piss off the one person actually in there doing the work, although having one person around is good in case you get stuck and need someone to pull you out by your feet, check continuity on something you can't reach, and sometimes to drink some water and stare at the infernal contraption while you commiserate and wonder why you ever decided to do this to begin with.

It was offline all day today as they worked on it - and yes, they're going to make it right entirely. We actually have two A&Ps (or one A&P and his trainee) who are paid by the club at an hourly rate. Thankfully the club doesn't mess around with MX. Right now about half our fleet is shuttered for various MX and waiting on parts, but our club members get that this is the price of careful MX.

 

[Roger Roger]

Long story alert. The weirdest electrical issue I ever troubleshot involved a set of Cessna Caravan airspeed switches. The airspeed switch that controls the BELOW ICING MIN SPEED annunciator burned out, so we replaced it. Promptly fails again. Install a second one, notice that it ops checks ok while hanging by the wire harness and pitot/static lines, but as soon as we bolt it in place, it fails (accompanied by magic smoke smell) and nothing will bring it back.

Ok, clearly something is going on here. Since the problem comes when it’s installed, I check the mounting bracket for voltage. Sure enough, the mounting bracket is showing 24 VDC. At that point I go through pulling circuit breakers until the voltage goes away. The circuit breaker that fixed it was the Overspeed warning, which has another airspeed switch mounted to the same bracket.

Turns out the overspeed switch had shorted internally and was sending power straight to ground through the case. But, since the bracket was a later installation (part of the Caravan icing ADs), and had been apparently very thoroughly painted before installation, isolating it from aircraft ground, it wasn’t tripping the breaker. So the icing airspeed switch was providing a path to ground all backwards, burning it out in the process. 2 new airspeed switches, and a little work with sandpaper to properly ground the bracket, and we were back in business.

 

[killbilly]

Long story alert. The weirdest electrical issue I ever troubleshot involved a set of Cessna Caravan airspeed switches. The airspeed switch that controls the BELOW ICING MIN SPEED annunciator burned out, so we replaced it. Promptly fails again. Install a second one, notice that it ops checks ok while hanging by the wire harness and pitot/static lines, but as soon as we bolt it in place, it fails (accompanied by magic smoke smell) and nothing will bring it back.

Ok, clearly something is going on here. Since the problem comes when it’s installed, I check the mounting bracket for voltage. Sure enough, the mounting bracket is showing 24 VDC. At that point I go through pulling circuit breakers until the voltage goes away. The circuit breaker that fixed it was the Overspeed warning, which has another airspeed switch mounted to the same bracket.

Turns out the overspeed switch had shorted internally and was sending power straight to ground through the case. But, since the bracket was a later installation (part of the Caravan icing ADs), and had been apparently very thoroughly painted before installation, isolating it from aircraft ground, it wasn’t tripping the breaker. So the icing airspeed switch was providing a path to ground all backwards, burning it out in the process. 2 new airspeed switches, and a little work with sandpaper to properly ground the bracket, and we were back in business.

I need someone to give me a thorough 101-level, hands-on exercise in troubleshooting aircraft wiring and use of the multimeter. Getting ready to attack a complete panel refresh and I'm reasonably certain that - even with pre-built harnesses - this is something I'm going to have to learn, probably the hard way.

 

[Roger Roger]

I need someone to give me a thorough 101-level, hands-on exercise in troubleshooting aircraft wiring and use of the multimeter. Getting ready to attack a complete panel refresh and I'm reasonably certain that - even with pre-built harnesses - this is something I'm going to have to learn, probably the hard way.

Man, if I lived nearby…DC is easy. AC is witchcraft.

 

[killbilly]

Man, if I lived nearby…DC is easy. AC is witchcraft.

It's easy when you know what you're doing. It's $#%#$ witchcraft when you don't.

It's something I can learn, sure, it's just not something I wanted to learn on the fly.

 

[drunkenbeagle]

Typical GA wiring

I assume that Part 43 Appendix A (26) Replacement or adjustment of nonstructural standard fasteners incidental to operations. -- allows for appropriate replacement of zip ties. I've added a few where exactly this scenario was likely to happen otherwise.

 

[drunkenbeagle]

Man, if I lived nearby…DC is easy. AC is witchcraft.

RF is witchcraft.

 

[Roger Roger]

It's easy when you know what you're doing. It's $#%#$ witchcraft when you don't.

It's something I can learn, sure, it's just not something I wanted to learn on the fly.

I wonder if these days there aren’t online tools you can use to learn some of the basics we went through in DC electricity class. Seems like a DC troubleshooting training app wouldn’t be hard to do. Just remember, in DC Ohms law rules all.

 

[Roger Roger]

I assume that Part 43 Appendix A (26) Replacement or adjustment of nonstructural standard fasteners incidental to operations. -- allows for appropriate replacement of zip ties. I've added a few where exactly this scenario was likely to happen otherwise.

Your mechanic will appreciate it if you make sure to cut the ends at a 45° angle.

 

[killbilly]

I wonder if these days there aren’t online tools you can use to learn some of the basics we went through in DC electricity class. Seems like a DC troubleshooting training app wouldn’t be hard to do. Just remember, in DC Ohms law rules all.

I'm sure Youtube will come to my rescue.

 

[drunkenbeagle]

I need someone to give me a thorough 101-level, hands-on exercise in troubleshooting aircraft wiring and use of the multimeter. Getting ready to attack a complete panel refresh and I'm reasonably certain that - even with pre-built harnesses - this is something I'm going to have to learn, probably the hard way.

The shop manual wiring diagrams are pretty simple, at least on my plane. 12v goes to a breaker, possibly to a switch, to some device, and then to ground. Normally, you are checking for 12v where you expect it, and a ground where you expect it. The "continuity" function is the 2nd most useful part of the meter (tells you if 2 things are in fact connected or not, like a ground another ground).

 

[Wardogg]

It's easy when you know what you're doing. It's $#%#$ witchcraft when you don't.

It's something I can learn, sure, it's just not something I wanted to learn on the fly.

It's relatable to the wiring in your car. Everything is grounded to the frame. Which all leads back to the negative terminal on the battery. If you are testing something for voltage you should be able to test the wire and any metal part of the aircraft. Now chasing shorts is a whole other ball game.

 

[drunkenbeagle]

Your mechanic will appreciate it if you make sure to cut the ends at a 45° angle.

Cut the ends? That sounds like way too much attention to detail.

 

[drunkenbeagle]

Getting ready to attack a complete panel refresh and I'm reasonably certain that - even with pre-built harnesses - this is something I'm going to have to learn, probably the hard way.

I would strongly consider these: Welcome to Approach Fast Stack

 

[killbilly]

I would strongly consider these: Welcome to Approach Fast Stack

Harnesses are already custom built for my setup. I just gotta put it all together.

 

[Roger Roger]

The shop manual wiring diagrams are pretty simple, at least on my plane. 12v goes to a breaker, possibly to a switch, to some device, and then to ground. Normally, you are checking for 12v where you expect it, and a ground where you expect it. The "continuity" function is the 2nd most useful part of the meter (tells you if 2 things are in fact connected or not, like a ground another ground).

Then properly terminating wires is a whole nother subject especially when you get into pinning connectors and using shielded cables. Not rocket surgery but there’s a lot of sloppy work that gets done

 

[killbilly]

Then properly terminating wires is a whole nother subject especially when you get into pinning connectors and using shielded cables. Not rocket surgery but there’s a lot of sloppy work that gets done

Garmin (I think it's Garmin) has published a couple of videos on proper termination and wiring for all the CANBUS stuff they do. It's pretty cool. EAA is also sponsoring a LOT of classes on everything from sheet metal to wiring over the next few weeks. I may attend a few.