Your assumption that jumpering the 15 & 30 pins of the seat heater relay would cause the heater to remain ON, would be correct if it stayed in the earlier car BUT not when used in the '93 that was asked about. In the later car, the console switch controls the "30" supply, making it switched by both the driver control and by ignition.

Thanks for the detailed responses.

I have closely examined the circuit boards for both the 1990 and 1993 leather seat heater relays. Except for one connection, the circuit board and electronic parts appear to be idential on both relays (the numbers on the NEC chip are also slightly different). The one difference on the circuit board is that on the 1993 model the circuitry has a direct connection between the area where pin 15 (pin 30 on the 1990 model) joins the circuit board and the area where pin 30 (pin 15 on the 1990 model) used to connect to the board (when comparing to the 1990 model). Therefore, it would appear that making a wire connection between pin 15 and 30 on the 1990 relay does exactly what is done on the updated 1993 circuit board.

In addition, in the 1993 Volvo there is no wire connected to where pin 15 used to be and pin 30 has been renamed pin 15. The 1993 model has three wires connected to the relay while the 1990 model has four wires.

Does this affect your response?

Thanks for all the help.

My seat heaters in my 1993 945T+ are now working great using the replacement relay from a 1990 760 and following the suggestion provided by Mapleleafer. I did join pins 15 and 30 by soldering a copper wire between the pins inside of the relay. The heater does not stay on after turning off the ignition even if the switch is on.