Making outgoing calls to local PBX

I have am old PBX system that I would like to also add an asterisk server into. I have a TDM400 card with an FXS and FXO card installed. I have everything installed and I can make calls from the old PBX into the Asterisk system, but I can’t make calles from the Asterisk system out to the PBX. I have the old PBX line coming into the FXO card. I have created a trunk and an extention like it says to do but I can’t get it to work. Anyone have any ideas?

whats does asterisk show when you try to make the call?

Questions questions
What want your old PBX - for dialing? Tones or pulses?
Is there dialtone?
How you connect Asterisk to PBX - which modules you are using?
How you are making call? Can you show us dial string?

I have our old PBX system coming into the FXO card and I can have an IP phone ring when I call the number of the old PBX system. for example the old pbx extension is 7003 when it comes into asterisk it will ring extension 200. That was easy to get going. But now I want to know if it is possible to use the same FXO card to then call back into the old pbx system. I was able to get it going by setting up an extension tied to zap/4, which is the FXO card but then I couldn’t call into asterisk from the old pbx. I have another FXO card on the way as I have a feeling you can’t have 1 FXO card do double duty