I did in fact relocate the relay when I replaced the solenoid, it is now right at the rear of the starter mounted to one of the solenoid mounting screws.
Ignition switch with Start Relay.pdf
Above is the wiring diagram for a
POSITIVE GROUND 1965 SP310.
Just ignore the wire polarities and follow the wiring alterations
The existing solenoid wire is re-directed to pin
#85 of the relay, the coil pin.
A new wire from pin
#87, one side of the make contact, is connected to the starter solenoid connection that the Ignition Switch wire was originally connected (above).
A new wire from pin
#30, the other side of the make contacts, is connected to the main battery cable terminal at the starter motor.
A new wire from pin
#86, the other side of the coil, is grounded: I used the starter motor mounting bolt with a large eye terminal.
I like using Bosch relays, always been reliable for me
The relay used in this instance is a Bosch
0332019451 12V 30A 4 pin: -
There is a schematic printed on the case and all the pins are clearly numbered

I also used a relay socket so that in the event of failure, I can change the relay simply and easily.
BOSCH 3 334 485 008 Relay Socket.
This improvement has been in use for years in my SP310 and will save your Ignition Switch START contacts from the high solenoid current.
Any questions just let me know

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