HELP! 98 bonneville ext temp flashing-no heat

Recently the check engine light came on and was flashing. We started by replacing the plugs and found bad plug wires. This solved the problem for the check engine light. It took about 7 starts to turnt the light back off. We had disconnected the battery also. Now the ext temp is flashing and the heater is not putting out even warm air. It worked fine before the plugs, wire and battery. Does anyone have ideas of what I should try or check first? I live at least 100 miles from the nearest shop and would like to try some options before I take it in.

Thanks!

P.S. it was only 7 degrees this morning and I get home way after dark too.

Check your coolant levels. Hope that helps.