1. Are these 2 or 4 wire devices?
2. What zones are these devices connected to?
In general, a 161 would be a trouble indication for a NO zone with 1K EOL resistor installed. If you remove the device wiring from the zone input and just strap a 1K, 1/2 watt resistor across the contacts of the zone (+ to -), what sort of loop reading do you get? It should read approximately 145-148. If the resistor by itself works properly, you have some sort of wiring issue.