Hafler DH 500 relay

The relay is a Hafler part number 334002 or SZ113.
I think the relay can be replaced by a NTE R10 series 2 pole single or double throw relay , DPDT relay. I do not know the relay operating voltage , I think it is 24vdc but not sure.
Try a NTE , R10-11D10-24F This is a , DPDT , Double Pole Double Throw relay with a 24 vdc operating voltage.
Try to measure the voltage on your existing relay when it operates. You can also measure the resistance of the coil of your relay , it should be around 470 ohms for a 24 volts coil. You can adjust the value of R120 , 1500 ohms 2 watts , for the correct relay operating voltage.
Hope this helps
Ed