The kickdown relay as used in 928 model with automatic transmission comes in two versions. Difference is the A-signal.
Porsche 928 models 1983-1987 : 928.618.109.00 (PET says it is for 1983-1986 but also the 1987 and 1988 have analog clusters and the A signal appears in the schematics of 1989 when the digital cluster was introduced)
Porsche 928 models 1989-1995 : 928.618.108.00 (PET says it is for 1987-1994, but the A signal on this relay appears first in the schematics of 1989 when the digital cluster was introduced)
So... I think PET is not accurate.
Signals are:
Pin 30: This gets 12v from bus 15 (switched 12v) via the kickdown switch under the gas pedal.
Pin 31: ground
Pin 15: switched 12v from ignition key
Pin 87a: connection to kickdown solenoid at transmission
Pin 31b: speed (rpm) pulses from EZK (EZF) to LH
Pin A: digital output form Digital instrument cluster (only existing in the 1989-1994 models since they have a digital cluster)
Some comment on how it works:
when the kickdown switch is open pin 30 does not carry 12v, no power goes to pun 87a. We are in normal operation. When the kickdown switch is closed the Relay gets 12v on pin 30, and via the relay contact 87a to the solenoid. That is when we are kickdown mode. As the transmission should still respond to speed and rpm, two signals are added: 31B and A, so that it knows how fast we go and what rpm the engine makes. Depending on digital speed signal from the cluster and speed pulses from the EZK, the relay opens, causing the solenoid to de-activate and transmission upshifts normally.
From the 1989 service info manual:
Kickdown Relay (Speed Relay) with Two
Shift Points
The 1st -P 2nd gear shift of the old kickdown was carried out hydraulically at
an engine speed of approx. 5,000 rpm with large tolerances.
Upshifts from 2nd to 3rd gear and 3rd to 4th gear with the accelerator pedal in
kickdown position were introduced via the kickdown relay at an engine speed of
5,900 rpm.
The new kickdown relay uses the engine speed and road speed information to know,
in which gear the car is being driven at the moment.
It has two shift points.
For 1st + 2nd gear kickdown shift: at 4950 +/- 50 rpm.
For other kickdown upshifts: at 5950 +/- 50 rpm.
regards Theo
1992 Porsche 928GTS midnight blue