parts interchange- fuel pump relay 300sel vs 420sel

[ericzacha]

Does anyone know if I can use a fuel pump relay from an '88 420 SEL on an '88 300 SEL? They look exactly the same and they have changed the 300 sel replacement from the original 9 pin to a 10 pin just like the 420. I am having surging/decelerations at all speeds with variable RPM's at stoplights. While on the freeway at 70mph it feels like I'm suddenly hitting a stiff breeze for a second or two, and then the car recovers and continues at same speed. I was going to start with this, then move on to OVP etc if it doesn't work.