Telephone "off-hook" indicator

Question

I have a 2-line telephone that shows when a line is in-use (i.e. if an extension is picked-up, the indicator will light up on the phone). The two lines are being supplied via 1 RJ-11 cable (1 line on each pair). Both lines are supplied via the wiring throughout the house but here's the issue: - The lines DO NOT show as IN-USE when both phone lines are connected to the telephone

When 1 line is connected to the phone, the indicator lights up when an extension is picked up. I've tried both lines individually and the indicator seems to work fine. The issue only seems to happen when both lines are connected. I suspect the voltage is not dropping (indicating an off-hook) but does anyone have any suggestions on where to begin troubleshooting? Thanks.

Answer 1

I would investigate whether both lines have the same polarity. This used to be important, but modern phones don't seem to care, so installers connect house wiring to the phone lines without observing tip/ring polarity. It may be that one of your lines has tip/ring reversed, and your indicator circuits can't handle that.