A precious reference here
Here is a precious thread listing where are the various relays. http://au.rrforums.net/cgi-bin/forum/discus.pl?pg=prev&topic=17001&page=15292
Source: The Rolls-Royce Forum - Australia

How to identify a relay anyway ?

There are two or three methods or more :
1- the clicking coming from inside the relay when you operate a switch.
2- the Work Shop Manual on section M10 lists several relays but I have to say that it lacks precision and does not always match your particular case
3- the colours of the wirings to which the relay is connected : note them and refer to the theoretical diagram that matches your car (again there may be some difference with your particular case)
For example on the picture you notice a dirty Blue-Yellow plastic wiring which suggests according to the Lucas colour codes a link to the headlamp
Source: Diverse

Relay map in progress
As shown on the wiring diagram (1973) from top-left to bottom right

Relay name

type

Location

wiring

Relay name

type

Location

wiring

Starter relay

?

?

C

-

C

-

-

P

-

C

Auto-Park relay

?

?

C

-

P

-

P

-

-

LH seat relay 1

?

?

C

-

-

P

-

P

-

LH seat relay 2

?

?

C

-

-

P

-

P

-

Source: Diverse