Ignition Switch Question

[Namerow]

I have a question for the electrical experts:

I bought a Beck Arnley aftermarket ignition switch to replace the 40-year-old OE switch in my '70 Z.  Seemed like a good preventative maintenance step, with the steering column currently out of the car.  However, I've found puzzling difference in the operating logic of the two switches. It has to do with the switches' 'R' circuit, which I'm pretty sure means, 'Resistor' (as in, ballast resistor for the coil/tach circuit).

With input power applied to each switch module by way of the 'B' (battery) terminal and output monitored at the 'R' terminal, this is what I find:

Key Position                   "R' - OE Switch                                      'R' - Aftermarket Switch

OFF                                   dead                                                        dead
ACC                                  dead                                                        dead
ON                                    dead                                                        dead
START                              live                                                           live to start, then goes dead when key is turned further against the detent spring

It's been noted elsewhere that the Z's ignition circuitry is designed so that the ballast resistor is bypassed during engine start (so as to deliver higher voltage to the coil/points) and then brought back into the circuit during 'run' operation (so as to operate the points/coil at the lower, normal voltage).  So a 'live' condition at the 'R' terminal of the switch means 'resistor out', whereas a 'dead' condition equates to 'resistor in'.

My OE ignition switch adheres to this simple, two-step 'resistor out/resistor in' logic.  The aftermarket switch does too... at first.  But then as I twist the key a little further in the 'START' sector, working against the resistance of the internal spring to take the key all the way to the hard stop, the switch action reverts to 'resistor out'.  This would typically be where the key would sit while cranking the engine (i.e. twisted all the way up to the hard stop)

I'm not certain whether the aftermarket switch was designed this way on purpose, or not.  There's also the possibility that it's just a defective unit.  So now I'm not sure whether I want to use it.

Does anybody have an idea about why the aftermarket switch would change from 'resistor out' to 'resistor in' halfway through the 'Start' segment?

Could it be that this was done on purpose, so that the duration of the high voltage ('resistor out') condition in the coil/points circuit would be restricted to just the first part-rotation of the crankshaft, so as to avoid burning the points during prolonged cranking?

Edited June 23, 2017 by Namerow
New thought added

[Zed Head]

1 hour ago, Namerow said:

START                              live                                                           live to start, then goes dead when key is turned further against the detent spring

Not really clear (to me anyway) what you mean by "further against the detent spring".  Are you saying that the Start position has two states?  Start is at the end of the cycle so there shouldn't be another position beyond it.  Sounds like a loose switch that is passing its contact point.  Defective.

Pretty sure that SteveJ has written about the differences in the Ignition switches, in the past.

@SteveJ

[Namerow]

Nope.  Nothing's loose.  The detent for the Start position (for either switch) isn't a 'click-stop' detent like the other positions.  The Start detent actually provides 5 or so degrees of key travel before the key runs up against a hard stop.  During that travel, the key rotation is resisted by an internal spring.  It's something you probably wouldn't notice when you're doing a normal engine start, but you'll notice it right away if you try operating the key with the battery disconnected.   It's probably there to provide a cushioned stop for the key when the operator is extra-energetic about trying to get the engine started.

[Zed Head]

"Loose" was a poor choice on my part.  How about poorly or incorrectly assembled?  The rotating mechanical parts are misaligned with the rotating electrical parts.  

So your basic question is "Are there supposed to be two electrical circuits possible in the one Start position of the switch?"  

Seems to me that if Nissan intended two circuit possibilities that they would show two circuits possible at Start in the wiring diagram.  Anyway, might be fun to have a few people test their spare switches.  I have a 78 280Z switch in the garage, but they stopped using the ballast in 78 so don't know if it would be the same.

[Zed Head]

Here's something that might be illuminating - what happens to the circuit  to the starter solenoid when the power to the R terminal switches?  If you don't get power to the starter solenoid then the R terminal is kind of irrelevant.  Instead of looking at key position look at solenoid power.

[Namerow]

Nope.  The 'S' terminal becomes and stays 'live' over the full range of key travel in the 'Start' position.  Same for both switches.

I don't necessarily disagree that there might be something wrong with the internals of my Beck & Arnley switch, but the housing halves are staked closed so I'm not interested in try to get it apart to see what might be going on.

Maybe somebody else has got an aftermarket 240 ignition switch lying around loose that they could try the same experiment with.  Just to satisfy my curiosity.

[Zed Head]

So, to summarize - within the range of the Start position,which is essentially just off of the Run position, your switch completes the S circuit immediately and holds it, but loses the proper R circuit after a certain amount of rotation.

Looks like 1978 still has an R but I can't find a diagram that shows it connected to anything.  I'll dig mine out if I get out there.

[Zed Head]

That was interesting.  I pulled down my 78 parts box and the old switch was right on top (meant to be!).  I hooked up some leads so that I could easily turn the key and listen to my meter-beeper (I know CO doesn't like them but mine has a readout to watch also) and found that R had continuity with B right away and to the end of rotation, but S was iffy and seemed to only have one narrow range where it had continuity.  Then I remembered that I had pulled it apart in the past when I had a problem with my 76, and had ended up bending the internal actuating rod to make it work right.

Testing with the switch pulled apart and turning  the electrical portion with a screwdriver showed that both S and R could be over-rated to where they lost continuity.  The only thing controlling the total degrees of rotation is the mechanical (key) part of the switch  So I'd guess that your new switch is just adjusted to turn the electrical switch too far.  Not good news but it can be fixed, if you unstake it and take it apart.  You can twist the flat rod with a pair of pliers.  But I don't think it's right, it's a flaw in operation.

One big "Ah Haa" from back when I used to start the 78 parts car is that now I know why it would start to turn over then let go all of a sudden, leaving the starter spinning loudly.  I thought it was a starter problem but now realize that it was just the ignition switch rotating past the contact and losing the S circuit.  I spent a lot of time trying to reason that problem out and never really had a good theory.

 

Edit - more interesting stuff.  I noticed that the brass male S pin was wobbly on the back of the switch.  So I restaked it with a drift pin, put the whole assembly back together, and both S and R worked as expected, full continuity over the full Start rotation.  So, check the pins on the back, maybe R is loose and can be reset with a little tap of a hammer.

Edited June 23, 2017 by Zed Head