I recently bought a 1981 r107 380sl and the fuel relay has been giving me issues. the relay ticks when the car is on and i am assuming this is frying it. I have been through two relays so far (the first was the one the car came with, second was a reproduction I bought) and it looks like the third, which is an original, is on the way out. Does anyone know what's could be causing/how to fix this?

The 1981 year used two different relays.
Six pins, or twelve pins (nine used).

Its the 6 pinned one

Does the rate of ticking change with engine speed?

With the first two, no. The ticking sound was constant. The third is better but I have recently noticed that it to has started ticking as well.

If the tick rate is constant, the engine speed signal (TD) is probably not involved.

The relay supplies power to two devices: 1) the fuel pump, & 2) the control pressure regulator, aka the warm-up regulator (WUR).

The WUR is mounted to the right of the distributor, and slightly aft. It has two steel fuel lines connected to it, and an electrical plug. The electrical plug is for a heating coil in the WUR. Pull the plug out; does the ticking stop?

No it does not stop. So im guessing its the fuel pump then.

according to the etm, there's only 4 wires for that relay. 30 is 12v to power the pump and control press reg when the relay closes. 87 is power to them when it's closed. td is tach signal shared with the ignition module and tach. this makes the relay close. pin 5 is power to the lambda relay.

i can't explain the ticking. burning up the relay is probably the fuel pump drawing too many amps-old age, most likely.

i'd fashion a jumper harness for access so i could see what's going on, causing the clicking, amperage drain from the pump, etc.

329:

Porkface is indeed correct about there being a connection to the lambda control; the fuel relay supplies power to the frequency valve. Are you familiar with the frequency valve? If so, unplug the 2-pin connector on the valve. Any change?

Apologies for the late reply, I unplugged the valve no change.