Are the cables still connected to controls or whatever at one end? If so, any continuity test might be confused by sneak paths through the controls (multiple conductors will be connected through closed contacts or low impedance relay coils).
If there are terminal blocks available, its best to disconnect one conductor at a time and test it at the (disconnected) far end of a cable. That doesn't take as much time as it sounds. I use a continuity tester with an audible signal and brushing the probe over all the free conductors a few times, listening for the beep narrows it down pretty rapidly.
Yep, this is the point everybody missed. The operator panel is all soldered up and I don't want to take anyting apart in there. it would ruin it. I don't need to just trace a wire from one end to the other, I need to know which wire is connected to which switch.
(This goes a lot faster than my explanation implies.)
Start by shorting the two probes together to confirm the meter will beep properly.
Place one probe on pin 1 and move the other probe to pin 2 - 50 in sequence. Record all beeps. Move your probe from pin 1 to pin 2 and repeat your scan with your other probe.
If a pin beeps to any other pin, write that down. 'Pin 5 to pin 32' for example.
Eventually you will find a pin that beeps to a lot of other pins. (Often, many of the even - numbered pins or odd - numbered pins.) If these pins also beep to a ground point on the control panel, you have good evidence to support the theory that you found your ground connections.
Confirm this by switching to normal 'ohms' mode and check the 'beeping' connections once more. You should see that there is no difference in resistance between 'shorted probes' and your suspected connections. Remove any connection from your list that appears to exceed that resistance by say 0.7 ohm or more.
Example: With probes shorted together, you see that the meter reads 0.2 ohm. All the valid connections will read no more than say 0.9 ohm. (Practically speaking, your valid readings should also be in the 0.2 ohm - 0.5 ohm range).
A pin reading higher resistance should be dropped from your list (unless it is just a dirty connection that you can polish and bring under 0.9 ohm).
Use alligator clips to connect your beeping ohmmeter to your ground connection and hold the other probe in sequence to each of the pins that did not beep.
Press each button on the control panel till you hear your meter beep. Write down the pin number and button logo.
You can run this inspection in about 1% of the time it would take to build your terminal strip.
We didn't miss it, you didn't give much background detail so I posted a generalized cable tracing procedure.
Is this unit completely passive, only lights and switches, or does it contain active circuitry? Even relays count, coils with kickback diodes have a polarity and you may have to energize them to find the normally-open contact.
How easily can you connect to it? Are you holding meter probes on pins or can you plug in a wired connector and make solid hands-free connections?
Passive, several lamps, pushbuttons, rotary switches, and a few toggles. One MPG (manual pulse generator - like an encoder)
Right now I have two 30' cables with an end on it that plugs into a Fanuc 6 computer board header. The cables are at least 20' too long. Somebody suggested all the spares are likely tied to ground. It looks like on the computer end only. I don't have the compter here right now and i can't find any conductors going to ground. I'll get the computer back and focus on finding the spares first. Like somebody said, this will cut the problem in half.
From there, I guess I'm planning on hooking each wire up to an Opto22 input. They have an LED that will light when they see power. Its only fifty wires, once its all connected i should be able to toggle an input and see which opto fires.
If you can put stripped, numbered wires in the mate of that Fanuc connector you can check resistance between each wire and all the others, clipped together.
Closed switch contacts are shorts which open when you flip that switch, lamps should show a filament resistance. You might be able to make them glow slightly by powering them with a battery and series limiting resistor or light bulb. But be sure the voltage and current from the battery won't hurt anything. A car side marker bulb might work.
After you marked and eliminated the bulbs and closed contacts, the open contact wires should be easier.
Was this a single bundle? Usually there are color markings on each wire.
I like the resistor idea.
Wes
-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
It was 75 identical single pair shielded audio cables. Each had a black and a white wire, and a braided shield. The building was wired decades before they put footage markers on wire, which would have helped. I could have found one pair and read the markings for the length, then made a chart to identify everything else.
A terminal block with the resistors is easy to make and keep in your toolbox. :)
I designed a unit years ago to put a string of pulses on up to 50 wires, and a display for the other end to count them, but it was going to be way too big for most jobs, so I never built it. If I was allowed some additional income by the VA I would redesign it and put it on the market. It would be a lot smaller and require less power with a MPU, instead of the early '70s discrete logic.
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