disconnected wire?

[Peter Ha]

Hey folks,
Noticed this wire disconnected inside cowling next to firewall. It's a Cessna 150M and haven't noticed before, anyone know what's for?
https://imgur.com/Ydh4nIw

 

[Ryan Klems]

That looks like a corroded and broke off side tab of a mounted fuse holder. Are there any nearby? Kinda looks like the bracket where there would be 2 fuse holders and a diode to the upper left of the photo.

 

[Salty]

It could be a wire left from something removed. Pretty hard to tell from here. Trace it back to the other end....

 

[NordicDave]

Hey folks,
Noticed this wire disconnected inside cowling next to firewall. It's a Cessna 150M and haven't noticed before, anyone know what's for?
https://imgur.com/Ydh4nIw

Surprising how many old Cessnas should or need a complete rewire. I'd be very concerned about the corrosion and fatigue on other spade tabs in the electrical system seeing your troubleshooting pic. Get the service manual and trace back that broken wire to it's other side to see where the broken end attaches. Suggest careful inspection of the remainder of electrical system for brittle wire, corrosion, and fatigued connectors.

 

[AKBill]

My Beech has wire numbers printed on the wires. So if it was a factory installation you could look it up on the wiring schematics.

 

[Jdm]

Yeah, you should run that one back, figure out where she goes. I’ll bet it’s something that was long ago deactivated. Like maybe a clock? Otherwise you would have probably noticed an inoperative piece of equipment.
Noticing your battery wires and contractors there. Mine were just as bad until I rewired it last year. I went with all new Cessna P/N contractors, and a shiny set of bad boy Bogart cables. Couldn’t be happier with that decision. Looks incredible now. Much better grounding, charging, starting power, etc.

 

[NordicDave]

I’ll bet it’s something that was long ago deactivated...

Maybe, I doubt it given the obvious signs of corrosion and likely metal fatigue these spade connectors experience from 40-50 years of vibration and wear.

 

[weirdjim]

One trick I've used on several occasions is to get a signal generator from an electronics buddy and fire it up on the broadcast band on an empty channel. Wire it to be broken wire end. THen take a pocket transistor radio and follow the signal from bundle to bundle until you get to the end of the bundle. From there on out, it is a relatively simple task to follow individual wires with the radio until you come to the end of one that still has signal on it.

I suppose you could use the antenna output port of an ELT and a handheld VHF radio, but I admit I've never tried doing it this way.

Jim

 

[Jdm]

Maybe, I doubt it given the obvious signs of corrosion and likely metal fatigue these spade connectors experience from 40-50 years of vibration and wear.

I agree that it likely became fatigued due to corrosion, and finally broke off due to vibration. I’m just saying that it’s probably associated somehow with removed equipment, or a deactivated system. Otherwise something would very likely be inoperative. Be sure to let us know what you find!

 

[NavAir]

I suppose you could use the antenna output port of an ELT and a handheld VHF radio, but I admit I've never tried doing it this way.

Jim

Only in the first 5 minutes of each hour...

 

[Doug Reid]

Put a vom between the wire and ground on megohm scale if it shows no continuity, most likely not connected to anything. The connector has been broken for a long time.

 

[weirdjim]

Only in the first 5 minutes of each hour...

Nobody is listening on 121.5 any more, so what is the difference? Besides, you are transmitting into a nonresonant wire antenna inside of a pretty good aluminum shield / Faraday cage. I doubt you could be heard at the other end of the airport.

Jim

 

[weirdjim]

Put a vom between the wire and ground on megohm scale if it shows no continuity, most likely not connected to anything. The connector has been broken for a long time.

Or the device it is connected to is turned off. Same result.

 

[Capt. Geoffrey Thorpe]

What it used to be connected to shouldn't be more than a few inches from where the broken end is. Got a mirror to look under whatever it is just to the left in the picture?

 

[NordicDave]

I agree that it likely became fatigued due to corrosion, and finally broke off due to vibration. I’m just saying that it’s probably associated somehow with removed equipment, or a deactivated system. Otherwise something would very likely be inoperative. Be sure to let us know what you find!

Yup, completely plausible and maybe likely.

 

[Ryan Klems]

Found a picture I had taken from a 210 that had a similar busted wire from a fuse holder for the ground power receptacle (which is why I said that's what it looked like to me).

 

[Dan Thomas]

What it used to be connected to shouldn't be more than a few inches from where the broken end is. Got a mirror to look under whatever it is just to the left in the picture?

Those are the clock and Hobbs meter fuses, and that busted wire is likely off one of them. In these old airplanes the clock and Hobbs have been dead for a long time and maybe not even installed anymore.

 

[Jdm]

Those are the clock and Hobbs meter fuses, and that busted wire is likely off one of them. In these old airplanes the clock and Hobbs have been dead for a long time and maybe not even installed anymore.

I agree completely. That, or maybe the external circuit as previously mentioned. Regardless, it’s gonna be something that’s not in use, or deactivated. No need for complex testing. Just clip the zip ties and run it back. Let us know!

 

[Dan Thomas]

Never seen a 150 with an external power receptacle, but it does show up as an option in the '69-'76 service manual. Cessnas that had the receptacle also had a diode and resistor on a small circuit board.

 

[Cap'n Jack]

I'm expecting to be corrected, but is it possible it is a broken ground wire? The lock nut I see seems to have light colored washer under it, then a darker color washer, then the bracket that hold the fuel strainer cable in place. Could the "light colored washer" be the other part of that wire, as a cable lug?

 

[Jdm]

I recently replaced a diode board. Not cheap. Here’s a couple of pics of what they look like

 

[Jdm]

I'm expecting to be corrected, but is it possible it is a broken ground wire?

Very likely a ground. Especially if it’s a redundant one, which could break without causing noticeable malfunction. Here’s a few before/after pics of the contactors and wiring I replaced. It could have been a corroded contractor ground like one of these..
Check out the new cables, and the fancy dedicated starter ground wire, STC’d for Cessna aircraft

 

[Dan Thomas]

I recently replaced a diode board. Not cheap. Here’s a couple of pics of what they look like

Cessna has parts breakdowns of stuff like that, but you have to ask Cessna or a savvy Cessna dealer. The diodes and resistor are much cheaper than replacing the entire board. Seems to me a diode is about $6, which is bad enough considering that you can buy 25 of them for about $6 in an electronics supply shop. On the restart Cessnas the Lamar master control unit is on the firewall and has the master, starter, alternator and aux power contactors in it. The diode is in it, too. But Cessna doesn't break it down that far; they have the contactors and bus bars and stuff but not the diode. The box is a Lamar vendor-supplied component and you'd have to buy the entire box ($2K?) if the diode pooped. I phoned Lamar and they gave me the diode part number and told me that it was just a commonly-available commercial part.

 

[weirdjim]

I see what look like four little DC motors, but don't see any diodes. If the diodes are just reverse spike snubbers, you can use nearly any diode rated for power supplies, like 1N4002 or 4003 to give enough reverse breakdown for the spikes. Care to share what diode Lamar uses?

Jim

 

[Dan Thomas]

I see what look like four little DC motors, but don't see any diodes. If the diodes are just reverse spike snubbers, you can use nearly any diode rated for power supplies, like 1N4002 or 4003 to give enough reverse breakdown for the spikes. Care to share what diode Lamar uses?

Jim

Those four little DC motors are the contactors for the master, starter, alternator and external power. The external power plug is on the right. See the little black line coming off it and curving upward? That's the diode lead. Can't remember the number now but it was maybe a 1N4006. It was in the 1N400X series, anyway.

For perspective, here's that box on the firewall of a 172. The black square thing above the battery.

 

[nrpetersen]

1N4001 to 1N1007s - Anywhere from 4 cents to about 25 cents each from Digikey. You might have to buy maybe 100 or so.

 

[weirdjim]

1N4001 to 1N1007s - Anywhere from 4 cents to about 25 cents each from Digikey. You might have to buy maybe 100 or so.

Digikey may sell by the hundreds minimum, but Mouser will sell onesie-twosies if you wish. The shipping will be a few bucks, but you can have as many as you want.

Jim

 

[NordicDave]

Those four little DC motors are the contactors for the master, starter, alternator and external power. The external power plug is on the right. See the little black line coming off it and curving upward? That's the diode lead. Can't remember the number now but it was maybe a 1N4006. It was in the 1N400X series, anyway.

For perspective, here's that box on the firewall of a 172. The black square thing above the battery.

View attachment 85253

Dan, That's an amazing clean plane! Is this some sort of complete rebuild?

 

[Greg Bockelman]

Looks brand new. Independence?

 

[Timbeck2]

Nobody is listening on 121.5 any more, so what is the difference?

Some of us have to listen, but I've been known to turn it off, especially during the superbowl, game 7 of the world series..or when all the meowing gets too annoying.

 

[Greg Bockelman]

Never understood the meow-ing.

 

[Dan Thomas]

Dan, That's an amazing clean plane! Is this some sort of complete rebuild?

That's just a photo I got off the 'net. It will be new airplane. We had one identical to it in the flight school.

 

[nrpetersen]

Actually Digikey will sell in amazingly low quantities. It is a policy of the company management to encourage hobbyists.