I should have said PPM (Pulses Per Mile) rather than RPM. That is what the Blue Wire --the one that connects to the coil-- does. That plus the DIP selection of the PPM scale, 4,000 has been suggested by some installers, sets the upper RPM limit. If 4,000 PPM is really 4,000 RPM, then the ST1300's speed would be 69 MPH in 5th gear. If you want your cruise control speed limit set for 89 MPH (5,000 RPM), then set DIP #1 to OFF and DIP #2 to ON.
Marshal
PS The following is from a Miata website. Read the second to last paragraph.
"
So, I got it all in and rechecked my connections (including the
RSW connection, the grey wire, to the speedometer), and took to the open road. Accelerating to 45 MPH or so I turned on the unit and pressed the
Set button--releasing the accelerator in anticipation of some controlled cruising. I instead got nothing, nada, zip--no cruise control, back to the shop.
I once again checked my wiring, and the control module's DIP switch setup. Everything seemed OK, but on a hunch I changed the
Tach signal source to
COIL, my reasoning being that the 1.6L Miata doesn't really have a modern type
ECM signal (the signal at the diagnostic connector is the same signal that fires the ignitor)--back to the road. Nothing, no cruise control...back to the barn.
I got out my wiring diagrams and looked at the
RSW. It's just a reed switch activated by the viscous magnetic coupling in the speedometer, one terminal connected to ground, the other just dead-ended at the
RSW terminal. I.e. it is NOT an active signal, it could "pull-down" a signal to ground, but it does not generate any pulses per mile. Remembering the
Speed Signal setting (DIP switch 3), I set that to
Tach Only and disconnected the gray wire to the
RSW terminal--back to open road...
I got up to 45 or so, turned it on and pressed
Set, and immediately felt the servo take over,
YAY!!! Let's try 60 MPH, says I...
Nothing, it won't lock in. Playing with it I found that it wouldn't
Set at any speed over 52 or so, and also 52 was as fast as I could accelerate to using the
Accel function--back to the garage...
Trying to control my frustration (and having to get this thing working before the wife got home and found out I blew $100) I got to thinking about this
PPM,
pulses per mile thing. The manual says this setting works in conjunction with the
VSS (
RSW in the Miata) signal, which I had now disconnected. But since the Miata uses a wasted spark ignition system I thought I might as well try the
8,000 PPM setting--I mean heck, the worst thing that can happen is that I let the smoke out of my $100 cruise control unit (and she can only kill me once)--back out to open road.
OK, 45 MPH locked, let's go for 60...
YAY!!! I'm cooking, so let's find a secluded place where the FHP doesn't go...
Cool, 90 MPH and locked!
That's it--don't bother with the
VSS (
gray wire), so there's no need to yank the instrument cluster. Set
DIP switches 1 & 2 for
8,000 PPM,
switch 3 for
Tach Only, and
switch 7 for
ECM (I switched that back when it didn't work on
COIL). I used it today on a 100 mile round trip to Jacksonville and found that it worked well, but seemed a bit sluggish on what passes for hills here in NE Florida. I stopped and changed the sensitivity (
DIP switches 4 & 5) to
LOW (
light vehicles with high HP) and that fixed it, it now holds the set speed within +/- 1-1/2 MPH or so.
So, the bottom line is that this is a nice, inexpensive, very compact cruise control kit that works well. The installation instructions are a bit too generic, and use inconsistent nomenclature, and the recommended connections and settings for the NA Miata (at least the 1.6L models) are just plain wrong, but once set up correctly I like it!"
