nlcrane wrote:Both relays are pin compatible and can be inadvertently interchanged. The dark blue relay (Hella 4RA 003 510-34), however, has our old friend the quench diode internally mounted across the relay coil terminals, this is to quench the reverse emf caused by the collapsing magnetic field on de-energizing and to prevent this reverse current from damaging any downstream components. The light blue relay (Hella 4RA 003 510-68) has no diode, but has a current limiting resistor mounted in place of it.
My guess is that the diode had shorted, so the relay could not energise and so the clutch couldn’t be pulled in.
I think you're right. The relays have a little diagram printed on the side. The dark blue one does indeed have a diode between two pins in the diagram, which isn't there on the light blue relay.
Very interesting stuff, I've definitely learned something new. So if the dark blue relay functioned properly, I would have never had an issue? According to the Haynes manual it should have been a light blue relay, but wouldn't the dark blue one be safer?