W126 Relay ?
 

1988-91 420SEL: Under the hood near the firewall are two, black relays. One is for the a/c system, the other the fuel pump relay. The one closest to the master cylinder I will refer to as being position A. The one closest to the centerline of the car I will refer to as position B.

Previous threads and images are still, as far as I can determine, quite confusing. As are the part numbers. I have searched many threads and images to no avail...

Part #002 545 18 05 (8Zyl.Klima, Verz.) was, supposedly, the historic part number for the fuel pump relay and is in position A on my '88s & '91. Most internet forums (including this one) NOW list part #003 545 25 05 (Vemo V30-71-0026) as the fuel pump relay. And show the 002 545 18 05 as the a/c relay, and it is also listed as a "multipurpose relay (ProgRama) in the 7 pin (2+2, then 1+2) configuration!

On one '88 the relay closest to the centerline is marked 89 8184 400!

Is position A (closest to the master cylinder) the fuel pump relay? Is position B (closest to the centerline) the a/c relay?

Are these relays interchangable? What is the correct part number for both applications?

Your kind consideration in the is much appreciated? In the past (long ago) I know I replaced a fuel pump relay, but my memory doesn't go back that far anymore.

002 545 18 05 is the A/C compressor cut-out relay, located in your position "B".
The fuel pump relay is in your position "A", and, over the years, has had a variety of part nos., such as 16 05, & 25 05.
They are not interchangeable.