Auto Neutral Switch
I have been having an intermittent problem where I turn the key to start the car and get nothing but that 'tick tick' from under the bonnet. After driving me nuts for a year, I think I may have found the solution.
I found that the +12V going to the starter solenoid (black and yellow) is usually at least 1 volt under battery voltage, and the resistance with the ignition switch set to 'start' between +12V and the terminal on the starter solenoid is several mega Ohms. I thought I must just have a bad connection somewhere, until I read on the forums that on a Series 3, there is no relay between the starter solenoid and the neutral switch, the current flows from +12V right down to the transmission, through the gear selector ('neutral safety') switch and back up to the solenoid.
The Gregories manual is a bit vague on this topic so I thought I would share my findings.
First, find the loom going down to the neutral switch. In my car the connections come out of the loom that goes across the back of the headlights. One with 2 pins and one with several, right next to the battery. We are interested in the 2-pin one. Put your Ohmmeter across those two pins on the transmission side. Park and Neutral should give a closed circuit (0-0.05 or so Ohms resistance). All other positions should give an open circuit. Mine was very inconsistent, very high resistance, and changed greatly within the P and N ranges (the selector has some play in it).
On the driver's side of the transmission you will find the switch:
Put the car in Park. Using a 19mm ring spanner, remove the nut on the gear selector shaft. Remove the gear selector rod from the shaft.
Using an 8mm ring spanner, remove the three bolts holding the switch to the transmission. They are not all immediately visible, you will need to move the switch back and forth to get to them. One is hiding in a shadow in the photo above. There others (if this one is at 2 o'clock) are at 10 o'clock and 8 o'clock. Once you have them out, rotate the selector fully towards the front of the vehicle and remove the switch. The loom is permanently attached and will probably be secured in the crevice up above the switch by a couple of flexible tabs.
Remove the switch and entire loom from the car. Remove the screws holding it together, taking note of the two smaller ones.
If yours is anything like mine was, the contacts will be pretty badly gunked up and there will be indentations at the normal starting position. Be careful with the three contacts shown on the right, they are just sitting there on springs. Take them out and clean them, I used metho and fine sandpaper on all the copper. Take the springs out and give them a little stretch.
Reassembly is a reversal of all of this. Make sure the gasket on the switch and the three contacts are all sitting nicely when you screw it back together. Now is a good time to check the resistance in the P and N positions (you will have figured out which ones they are by now).
Loosely bolt the switch back on. Using a bolt or similar of 4mm diameter, line up the two holes in the switch with it in the N position. Do up the bolts and remove the lining-up tool. Slide the gear selector rod back over the shaft so it is snug, then re-check that there is a closed circuit in the full range of the P and N positions. Mine would only go closed then the selector was right forward in P. Adjust as necessary (a multimeter with audible continuity check really helps).
Put the nut back on the selector shaft, do up your connectors, replace the cable ties you cut off, and you're finished.
Hope this helps!
Compiled by: adamjgs