A general view of a typical 6RA 4 terminal, 4 spade type

Four terminals but five spades

An alternative 4 terminal, 4 spade but with W2 in a different position and a C3 instead of a C1. This is a relay with a normally closed contact.

Five terminals and five spades, this has a 'changeover' contact i.e. when the relay opens it switches a common contact from a normally closed contact to a normally open contact.

Cylindrical Lucas relays used on later MGBs, designated 26RA, SRB402.

Cube-type Lucas 28RA relays also can be found on late MGBs, identical to current (pun not intended) after-market relays.

Terminal arrangement, pin 30 is usually adjacent to the mounting bracket

Internal circuitry of standard relays. Note that with S2 and S6 single diode protection the power supply to the winding must be connected the right way round or it will blow the diode, +ve must be connected to 86 and -ve to 85. Resistor protection isn't polarity sensitive, but doesn't give as much protection to the operating circuitry as diode protection.

Internal circuitry of power relays. S1 has a tungsten contact that closes first and opens last, and a lower resistance contact which closes last and opens first. The tungsten contact protects the lower resistance contact against the back emf and high current from large inductive loads. S2 has double diode protection, the series diode protecting the parallel diode from damage through reverse connection, if reverse connected the relay simply won't operate. As before +ve is connected to 86 and -ve to 85.