We had a Comdial Executech system and for the fax line there was a two way splitter plugged into the phone line port on the Executech box one jack on the splitter for was the fax line in and the other jack on the splitter went to a A-AI Light Control Module TA-1 from TT Systems Corp. What this did was if the fax machine picked up the line, the light on the phones would indicated that the line was in use and no one could pickup the line from the Comdial phones.

Now we have switched to a Comdial DSU II with Impact phones and I've hooked the fax line up the same way with this light control module, but it doesn't work with the DSU, if the fax machine picks up the line the Impact phones do not show the line as in use. Is there a way to get this to work with a DSU?