I've done some circuit tracing today after checking the wiring diagram for the fuel system in the Bentley manual and noticing the warm-up regular and auxilliary air valve connect to the same point for the +12 volt feed which comes through the fuel-pump relay, and both connect to the same earth point.
I could not for the life of me work out where the earth point was so after some head-scratching I opted to measure continuity of the earth connections using one of the battery hold-down studs (the thread makes a nice earth point for testing!), and found the earth continuity to be fine (less than
0.5 ohm).
The +12 volt continuity was ok (about 5 ohms), but when I started the engine and measured the voltage presented on the electrical connector pins for the warm-up regulator and auxilliary air valve, the result was less than 4 volts!
So my next step was to try measuring the voltage between the +12 volt contact for each device and the +12 volt supply coming from pin 87 of the fuel-pump relay (using the 2-pin connector wired directly to the relay socket to hook up one lead from the meter).
That gave a full 13.5 volts when touching the other lead onto the earth contacts, and about 10 volts when touching the +12 volt contacts.
This is making me think that the problem is the wires running back from the warm-up regulator and the auxilliary air valve to the +12 volt feed coming from the fuel-pump relay.
Does this seem like a sensible deduction so far?
Regards,
Craig.