Bill Janssen writes:

Agree corroded wiring connection as likely cause.

Go to each jack and put a *milliammeter* across Tip-Ring.
Start at the demark.

The milliampmeter should be in series with a 400 Ohm
resister. The resister represents the resistance in the phone.

Not needed at all, and misses the point. The phone is not a
fixed resistance; it's a small voltage drop that varies with
loop length.

The outside plant loop and the line relay at the CO limit the
current. Let's say you are 5000 ft from the CO; that's 250 ohms
right there. The line relay is say 500 ohms. Worst case, 60 odd
mA. In reality the line card will limit it to far less.

Nothing you can do to your end of the loop will damage anything.

Your goal is to see the max available current. If it's not
sufficient at a jack, but is at the demark; there must be a bad
splice in the IW. And measuring the voltage with a open circuit is
sorta pointless.

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