As I mentioned in my initial post last week, I’ve mounted factory Cruise Control Systems on the following Asian models: A 1985 Mazda RX-7, a 1990 Mazda Miata, and a 1991 Isuzu Rodeo. These vehicles used a stand alone system that operated the throttle plate using an actuator and a secondary throttle cable.
In all three cases, the wiring to support the control box, actuator, control switches, and sensors was built into the factory harness. Because of this, system installation was a matter of gathering the parts up, bolting them into the factory mounting points, and plugging into the existing harness connectors.
Because each system was so similar, I’ll walk through the steps used for the ’90 Miata, and make any additional notes as needed.
To start, I considered calling the local Mazda dealer to see if they had a factory kit. When I installed Cruise in the ’85 RX-7, I bought the factory kit, which has the advantage of new plastic retainers, printed instructions, and the assurance you’ve got every stupid little needed part. In fact, if you have a 1988 non-turbo RX-7, I found the kit pictured above on E-Bay for a mere $199.96.
However, I wasn’t in a big hurry to upgrade the Miata, so I just kept my eyes open at the junkyard. To determine the needed parts, I took a look at the cruise control schematic, shown above. The purple circles indicate components that were already present on the car, the green boxes indicate the four parts I needed, and the blue box identified a brake switch I needed to acquire, even though a the car already had a stop light switch (one of the purple circles).
As I mentioned in the previous post, early domestic Cruise Control systems used a vacuum dump switch installed on the brake pedal to provide a safety back up to the brake light input. The top diagram shows this system- If the dump valve was closed and the brake light off, the cruise control system would engage. Any other condition, and the Cruise Control disengaged.
The lower diagram shows the system used on the Miata- Instead of a vacuum dump, the system adds a second set of contacts to the brake light switch. With the brake pedal released, the light switch is OFF (open), and the safety switch is ON (closed). Any other condition, and the cruise control will not engage.
Therefore, in addition to installing the actuator, dash switch, control box, and control stalk, I also needed to pull the 2 terminal brake pedal switch out, and replace it with this four terminal version.
Mounting everything else was very simple. Threaded mounting points existed for the actuator and control unit, and a blank cover popped off to make room for the dash switch. I did have to remove the steering wheel to change out the turn signal stalk, but the new stalk easily swapped into the turn signal switch.
Oddly enough, I had to build a short harness to the main switch in the dash. According to the interwebs, certain trim levels have the connector for this switch, others have a connector for a fog light (as in my car), and some have a connector for both… This is the stuff that makes working on cars so fun!
That pretty much covers these actuator based systems. Next week, we’re going to discuss Cruise Control speed sensors (in painful detail), and then move on to the Ford and GM systems.