OT: Any Car Experts?

I don't see how this could work, since the relationship of engine speed to vehicle speed depends on what gear the tranny is in. I would think the vehicle speed pickup would have to be on a driveshaft, in the tranny or possibly come from the ABS system.

The aftermarket jobs I've used had magnets on the driveshaft that induced pulses in a little pickup coil. At low speeds, the pulses can get too small (low in voltage) to work well. This can be fixed by using a better sensor, as a Hall-type sensor which can sense magnets regardless of speed.

Some standard trans units DID use engine RPM, and if engine RPM increased at too high a rate it was translated as "clutch in or out of gear - SHUT DOWN!!) Since you cannot shift gears on a standard without disconnecting the cruise control, this worked. On automatics it works OK if the tranny doesn't downshift. If it does, it automatically shuts down. It was a common "feature" of a LOT of cheap aftermarket cruise controls in the seventies. On automatic trans vehicles you were SUPPOSED to buy the add-on speed sensor. Either the unit that fit on the tranny speedo gear or the magnets and coil that worked on the drive shaft. The units that were programmable for front wheel drive could be used on rear wheel drive and set to work down to something like 12MPH - or you could add more magnets.

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Well, maybe I should have said I "think" I know the reason it is there for...

Your Aerostar is an automatic I presume. With a standard or "stick" shift car, you should be able to set cruise in the lowest or 2nd lowest gear at 10 MPH without a problem.

Greetings Don, Follow this link:

you want to see a web page describing the tach connection for some cruise controls. If you don't care to, it just says what you said, basically. If the control is connected to the tach it depends what gear you are in for the speed of the car. Some of the cruise controls that connect to the tach output turn off when the revs reaches 4000 to avoid engine damage. Better to use the VSS (Vehicle Speed Sensor) or a drive shaft magnet to provide the signal to the control. Eric

I have a 92 ranger, 4.0 v6, stick, factory cruise.

25mph min, no matter the gear.

Dave

Does it turn off when you hit 24 MPH or less automatically like mine does?

Since my 96 Ranger (manual) came without, I added an aftermarket unit (Audiovox). Pretty easy to hook up, only need vacuum, a mechanical connection to the throttle linkage, and a connection to the "tach" signal. (Well, that plus power and ground, and the connection from the unit to its dash controller) It is set up so that one can also connect to the vehicle VSS if you want, but I chose not to for the same reasons you've outlined. There is a switch to tell it to use VSS or not. Works flawlessly in any gear, including first, with this caveat: it will only work over a slightly limitted RPM range. You can bias that range somewhat by changing the number of pulses per mile that it needs. I got it for towing a trailer on long trips, so I currently have it set a little high for better power, before that it was set too low (at the setting recommended by the directions) which was good for economy, but would kick out as too fast if I geared down too much. There is one more setting between those two, and if it gets to annoying me enough I'll probably use it, but so far it hasn't. I especially like it for driving 30 - 35, to keep my foot from getting me in trouble.

HTH, --Glenn Lyford