I had a mechanic replace my fuel pump and it keeps going bad! Should I replace the relay switch too

 

What are the symptoms? When you turn the car key to the on position, do you hear the pump run for a few seconds?
Have you had your Relay Control Module refurbished or replaced? Your fuel pump relay is located in the RCM. They are going bad because of age. You can get a new one from amazon, or have tighed1 refurbish it for about 60 bucks.
Also, what brand of fuel pump is your mechanic using? Bosch or Pierburg are the most reliable.
More information would be helpful.



This the RCM



This is the RCM I carry as a spare in my trunk. I had my original refurbished by tighed1. You can get a new one on ama zon.

 

As preventive maintenance I would replace the RCM ( relay control module ) and crankshaft sensor ( Bosch ) both available at the link below
$ 159 https://www.autohausaz.com/pn/MB-1705450305

 

Please explain what you mean by keeps going bad! Works for a short time? Doesn't work at all? Falls off car? Burns up? Blows fuses? How many pumps?
This will help all who are trying to help you.

 

You should stop taking the car to some fool who is not checking to be sure the pump is getting power.

I strongly suspect the issue is a weak/bad relay in the RCM, if you replace the RCM you will know if that is the issue. You can buy an RCM for $130-180 from various suppliers and replace it yourself without tools. They literally plug right in; you need NO TOOLS or skills to replace one, just pull ONLY on the connectors and not on the WIRES themselves and you are fine.
You can't even plug the wires in wrong because all the plugs are different sizes!

Its super easy.

You want the "Relay control module" for a 2003 Mercedes SLK320. You can say "Crossfire" but often, the price is higher for the SAME PART.