ML 17929 Can't tell when line is in use

Manual for ML17929 found here. Go through the installation instructions and make sure you're using the correct base cords for your set up. Make sure the phone number on line one is the same number on line one on all phones. These phones use a data link between the phones which is usually on line one. 

I've installed several of these small two and four line businesses systems and never had one that was failed out of the box. Just putting a plain phone ahead of the system and going off hook should light the line lamp associated with that line. You stated you have 3 phones and none of them worked correctly. 

We just bought these phones for our office too. We have four phones that are each plugged into one jack for both lines. Sometimes the line in use comes on on or two of phones and sometimes it's the light but usually there's no way to know someone is on the line. Also, for some strange reason the time changes when a call is received, no matter how many times I reset it. Any ideas?

The first thing I'd do is use a separate cord for each line and just single line cords, not two line cords. There's no way for me to know if you have line one on the same pins on all phones. You should also start your own topic as this one is nearly a year old. 

I was about to but I wanted to see what the solution for this one was. But so I'm understanding you, what you're recommending is that the jack be split into line 1 and line 2 so we can have 2 different cords to plug into the phone?

Yes, two pin cords, not 4 pin. This is to make sure line one is line one on all phones, unless you've already verified that. Most issues I've found with these phones is miss wiring.