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The Cruise Control 

Modifications For Using The 4100 Vacuum Servo


This is the diagram of the non 4100 ECU cars. Even though the Buick V6 Eldos have an ECU, they still have the yellow cruise module you want. An easy way to see if a car in question has this module is to look at the vacuum modulator for the cruise. (the vac servo on top of the engine) If it has two electrical connectors then the car has the module, if it only has vacuum lines then you're out of luck.

The cruise module should be obvious to spot, and is located under the driver's side dash on the Eldos. You'll see two connectors going into it, one comes from the speed sensor, cut it leaving a little slack. The other is a short harness. The harness extends to the brake switch, the cruise master switch, the coast/accel turn stalk, and finally to the instrument panel harness. All you need to do is unplug the connectors at the brake switch and at the master on-off. The wires from the turn stalk are grouped together and colored red yellow and green and look petite. You can unplug this too. See below for details.

That leaves the instrument panel connection. Cut the wiring as indicated on the diagram, leaving enough slack after the connector to do a little splicing later.

Now at your Eldorado.... Step 1: Pull the Cruise Fuse it's at the top corner of the fuse block.

The speed sensor connector wiring on the yellow module should have a brown, green and green-black wire. The 4100's buffer amp will have a pnk/blk wire, a blk/wht wire and a tan wire. The tan wire is connected to terminal B on the buffer. For this to work, the wire needs to be connected to terminal C. Unplug the connector and finagle the tan wire out of B, and into C. Now cut the tan wire and connect it to the green wire on the yellow module. You'll find that everything else on the yellow module's harness will plug right in to your existing equipment, except the instrument panel harness.
BTW, the buffer amp is under the driver's side dash next to the steering column. It's easy to pick out the three speed sensor wires side-by-side that plug in to it.

I hope you left enough wiring after the connector. Here's what you need to do...
*There's a black wire, connect that to a suitable ground.
*There's a gray wire, this is used to illuminate the cruise master switch at night. Connect this to the gray wire at the headlamp switch or cut 'F' at the old master cruise control panel connector and splice. This gray wire is the dimmable lamp output that the headlight switch rheostat adjusts.
*The yellow module wire goes to the 3 amp cruise fuse. The existing wire from that cruise fuse is pink with a white stripe and goes to the CC brake switch. This connector also has a brown wire and is plugged in next to the switch for the brake lights. Cut the pink/wht wire from that connector and connect to the yellow module wire.

I've found that different years have different end connectors for the set/accel turn stalk controls. Not a problem. If you find that the plug from the stalk has three contacts on one side and none on the other, then it will plug right in to the new harness socket. If it has 4 contacts, 2 on each side, then cut the wires on the other side of the old connector. Don't cut the 3 petite stalk wires! On my car, this left me with a blue, a gray and a gray/blk wire (see diagram below). Use your judgement to match up the three wires so red is to red, yellow is to yellow and drk green to the remaining. On my car the gray wire from the old connector went to the module's pink/blk. The blue went to the red and the gray/blk to the yellow.

The final two wires are what actually operate the vacuum solenoids at the cruise vac servo.

-There's a blue wire with a white stripe (3), this goes to the cruise vac solenoid.
-The other wire is green(A) and goes to the power valve.

Here's where the fun begins: At the 4100's ECU, unplug the orange connector and refer to the diagram below. Cut E,F,J,7 and 6. Pull the red connector and cut 2. The diagram below shows what's going on. The color names in blue are the colors of the wires on my '85, the diagram is from '83. Different colors, same locations. Cut them close enough to the connector that they can't short to any other wiring.

Now cut A and 3. Then, at the driver's side of the dash, you'll see bundles of wires coming from the firewall near the center of the firewall by the floor heater duct. You can actually pull the brown (7), green (A) and blue/wht (3) wires out of their harness bundling. If you can't identify what's what, take a pliers and pull on the freshly cut wires from the ECU side of the dash and note which wire moves at the other end. Now you have the wires you need.

-A is light green, and needs to connect to the green wire (A) at the yellow cruise module.
-3 is blue with a white stripe, and needs to connect to, you guessed it, the blue w/wht stripe wire (D) at the yellow cruise module.

There's one last thing to do. The vacuum valve needs to be grounded. Here's how to do it. The brown (7) wire that you pulled from the ecu harness just needs to be connected to ground. With the old on/off control panel connector left open, and the old brake switch connector left open, you should be set. Just plug in the connectors from the yellow module.