20/25 marker usage up to, and including series U (to GMU21):

  E51071-6, Bush (Ignition Wires), 1 ea, at the distributor, style P.

  E17793-8, Wire Bush, 1 ea, at the spark plugs, style Gp.

  E18449, Chater Lea spark plug terminals as used on the late Ghosts are called for on all of the 20/25's.

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As discussed on the 20HP page, even though E53204 is titled simply for '20HP' it is applicable to the later 20HP as well as all of the 20/25's. Both the LOP and GA are located on the RROC, 20HP disc under the Wire Fittings and Ignition Wiring headings respectively.

The right hand side note on page 1* of the LOP E53204 says: "J - 1 off ea required up to the end of 'U' series". Also on page 1 the LOP calls for 2 each of 6, E51071-6 (style P), markers. There was no E51070 (style Z) on the coil wire. On page 2* there is a callout for 1 each of 6, E17793-8 (Style Gp), markers with a note: "M - Not used after 'U' series". Taken together these notes tell us there was one set each of styles Gp and P used through the U series. The 7 series (O, P, R, S, TA, TB & U) to use these two styles were the first 1000 20/25's.

Nothing presented here tells us which style goes at which end of the wire. But from their first introduction on the R series Ghost through the 25/30 series, the style P markers were at the distributor ends of the spark plug wires.

This is the last time the Ghost style Gp markers were specified; they had finally been discontinued.