Issues with hardwired smoke detectors in manufactured home

PLEASE HELP. I have four hardwired smoke detectors in my manufactured home, two of them do not have any AC power to them. I didn’t realize this was a problem until I bought new detectors that show a solid green light when connected to AC power, and I saw that two did not have this green light so I assume this was a problem before the new detectors. I’ve checked with a tic tracer at the two that have power and I have power going in and out of them, but not at the two without power. Not sure where to look. The house is only three years old.