Cruise Control: Finally!

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I was hoping to get cruise control installed before our trip to Colorado in October.  It wasn't strictly necessary, however, and I was still addressing a number of other handling-related issues.  After driving 1200 miles each way without it, I kept it on my TO DO list as a priority.

Today I finally got around to it.  I had purchased a replacement connector, thinking that I had cut it off by accident, and did the same thing I did with most of the fuel-injection related components.  For all the connectors I didn't need, I cut them off and simply to taped the wires up, tucking them away in case I had a need for the circuits later.  It pays, before cutting off a connector, to ensure that you know what it's for, first!

I spent a few hours yesterday digging into my wiring harnesses looking for a set of nine wires that would be connected to this ten-pin connector.  The first wire, and the easiest to identify, is the gray one that turns the power steering unit on.  Whenever I thought I had found it, I hooked up a voltmeter, flipped on my ignition switch, and toggled the cruise control on and off using the controls on the stalk.  After about three hours of looking, I gave it up last night.

With a fresh mind on my afternoon off today, I spent some time looking at a harness that goes back behind the engine, thinking it might be buried back there.  It was a painful process and I scratched up my arm on some sharp edges, but I didn't find it.  Not all pain is gain!

The Suburban's original cruise control module was reinstalled.

I decided to start at the steering column and trace where these wires wend.  I could tell that the bundle was passing through the firewall on the vehicle's left side by the convenience center.  I looked at the bundles on the outside of the firewall, identifying where each one went, knowing that I had missed something.  When looking at a few bundles going under the fuse/relay center, I found one that didn't seem to be attached.  I pulled on it and found myself staring at the connector I thought I'd cut off!

So, I reinstalled the Suburban's original electronic cruise control module on the firewall.  I chose to see if the original cable could be modified to work with the 4BD1T, rather than trying to build an entirely new one.  Recalling some aftermarket cruise control installations I've done in the past, I picked up some pull chain components from Rural King.  I also salvaged a part that attaches a pull chain to a bolt that

Pull-Chain and cable stops were used to connect the cruise control linkage to the throttle. Note the angle-aluminum bracket used to hold the sleeve.

was still attached to the lower side of the bellcrank in the throttle linkage.  By flattening one side of a coupler and drilling a small hole in it, I was able to slip it over the stock cable and keep it from sliding off with a cable stop.  I used the bolt-to-chain coupler on the other end, using the cable stop that grabs the throttle linkage cable.  The pull-chain is a great idea, as it ensures that the cruise control system can only pull on the throttle lever, and cannot keep the driver from applying throttle when needed.

I also cut a piece of angle aluminum and made a square (12mm x 12mm) hole in it so that the cable sheath could snap in place.  When I got this together, I checked to see that the pull chain wasn't long enough to droop and touch the glow plug rail.  I'd hate to have a short here!

This morning, when I was still at work I realized that I really needed to add a switch to this system.  Because the Suburban was originally equipped with an automatic transmission, I needed a switch that would sense when the clutch was being used and cancel the cruise control.  The brake pedal has two inputs to the cruise control system.  One is normally open, and the other is normally closed.  Either one will cancel when switched from the normal condition.  The normally closed one is what got my attention.  By running this through a second normally-closed switch, either switch will cancel the cruise control.

This is a clutch switch that matches the 2000 K2500 pickup clutch assembly I used. It snapped in place perfectly and provided normally-open and normally-closed connections.

My clutch assembly is from a 2000 K2500 pickup, so I looked for an appropriate switch and picked up this odd-looking device on my way home.  The white plastic piece pops off, and this switch snaps onto the clutch pushrod.  The white part snaps back into place to lock it on.  When I got under my dash with it, it was obvious how it would fit and it was a perfect match.  Connections on the end provide normally-open and normally-closed connections.

I spent a fair amount of time looking for the appropriate purple wire under the dash.  When I thought I had it (several times), I used a test light with a needle point that can dig through the wire's insulation and a ground clip to check.  I was looking for a wire that would give +12V with the ignition on, but would shut off when I touched the brake pedal.  When I found it, I cut the wire, added some extending leads, and put the normally-closed portion of this switch in series with the brake switch.  Now touching either the brake or the clutch will result in an interruption of this signal, canceling the cruise control.

With these components installed, I went for a short test drive.  I got the Suburban above 30 mph, turned the cruise on, and hit the set button.  At first I thought it wasn't working, but then I started climbing a hill and the vehicle maintained speed.  Clutch use canceled operation, brake use canceled operation, coast and accel/resume functions were working.  Mission accomplished!

-Time for some holiday travels to try it out!