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.
The factory harness connector, just waiting to plug into the actuator
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.
A COAL for 24 years, but now owned by my daughter
Because each system was so similar, I’ll walk through the steps used for the ’90 Miata, and make any additional notes as needed.
The easiest option- A factory kit
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.
Miata Cruise Control schematic
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).
Two common safety systems- The vacuum dump valve and brake safety switch
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.
Both switches operate the brake lights, but the base switch does not include the safety switch contacts
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.
It’s a bitch to mount the Miata control unit, given it’s under-dash location. The RX-7 used a much easier to access location behind the driver’s seat
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.
The four connections I had to fabricate
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.
My Miata has been the only car in modern memory that lacked cruise. Part of me liked the simplicity of having to drive it the old-fashioned way and part of me missed it on those roads where I would use it on any other car.
It doesn’t surprise me that many Asian cars of that era came pre-wired. Back before they had manufacturing plants in the US, it seemed like a number of options such as cruise control and air conditioning were referred to as “port installed,” which no doubt allowed some customization once the cars were stateside.
Sadly, those days are fading away. I know for a fact lower trim Honda’s now use a dedicated wire harness with a reduced wire count.
Interesting, sounds like someone did the math and figured that that it is maybe cheaper to build a million of A and a million of B with a few less wires in it than building two million of A. As pennies matter I can see this becoming more the norm again especially with larger volumes.
Not only that, in my newer Fords it’s impossible to add certain upgrades without some programming through ForScan, which is not for the faint of heart. And in some cases it’s practically impossible to add certain hardware (such as a navigation head unit into a non-nav vehicle) unless you know the VIN of the vehicle from which the unit came from.
On the other hand, adding extra gauges and such on our older vehicles is a simple matter of plug and play.
Reprograming with ForScan isn’t that big of a deal, though I don’t do it with my $12 dongle, only the $80 one. It was only mildly scary the first time and depending on which thing you are changing it is just a couple of clicks and the program “writes the code” for you. Others you need to know what digit to change and what to change it to, but for all but a very few items on the newest of new you can always change it back.
It is possible to program items with non-matching VIN w/o knowing the source VIN.
If all of that it too scary there are people who will program it with your VIN and even others that will put it on a Dongle that will automatically install said feature(s).
Similar with Peugeot/Citroen. When the dealer plugs into computer at services, it resets the car software to that applicable to the VIN. Our VIN didn’t have cruise ex-factory (I added it more recently using the factory stalk), so always defaults to off when plugged into the dealer computer. They can easily turn it back on, but as they don’t know that the cruise was added later, they don’t know to unless I remember to tell them.
Thats one of the things that scares me about messing with my car I’m not even sure the diesel manuals could be had with cruise manuals are rare enough anyway and all the computer systems work so I dont want to upset it resetting after an oil change is a simple affair resetting the clock for daylight saving has proved impossible.