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Lost cruise control after motor/transmission swap


vonD1025

Well-Known Member
U.S. Military - Veteran
Joined
Dec 20, 2018
Messages
88
City
Carson City, NV
Vehicle Year
1987
Engine
2.9 V6
Transmission
Manual
Total Lift
2 inch body lift
Tire Size
30”
So after switching the engine out to a rebuilt 2.9 and dropping a manual transmission in it I can’t get my cruise control to work. Any thoughts? I’m still using the automatic wiring harness and have a few unconnected plugs here and there.
 
When you changed it to a manual, you had to do some wiring to make it crank over correct? You had to jump the old neutral safety? If you swapped the pedal assembly, there were some wires that went from the cruise to the brake pedal to disable the cruise when the brake was pushed. Where these wires hooked back up? There was also a vacuum line with a vacuum switch under there hooked to the brake pedal. This is the cruise dump when you press the brake. Was that hooked back up properly or is it sitting there sucking vacuum?
 
When you changed it to a manual, you had to do some wiring to make it crank over correct? You had to jump the old neutral safety? If you swapped the pedal assembly, there were some wires that went from the cruise to the brake pedal to disable the cruise when the brake was pushed. Where these wires hooked back up? There was also a vacuum line with a vacuum switch under there hooked to the brake pedal. This is the cruise dump when you press the brake. Was that hooked back up properly or is it sitting there sucking vacuum?
Umm I don’t remember.. my dad and I did it like 8 years ago. I do have to start it in neutral every time. I’ll take a look at the pedals and see what’s going on.
 
When you changed it to a manual, you had to do some wiring to make it crank over correct? You had to jump the old neutral safety? If you swapped the pedal assembly, there were some wires that went from the cruise to the brake pedal to disable the cruise when the brake was pushed. Where these wires hooked back up? There was also a vacuum line with a vacuum switch under there hooked to the brake pedal. This is the cruise dump when you press the brake. Was that hooked back up properly or is it sitting there sucking vacuum?
Here is a few pics of it. I took a look but I’m not to sure.
 

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Tucked up behind the dash should be a big plastic box with a bunch of wires going to it. That is the speed control amplifier. See if you have that. You should also have a servo under the hood with a cable attached to the throttle.

There should be a lightgreen wire leaving the amplifier going to the lightgreen on the brake pedal switch. I thought this wire would be a normally closed circuit, but I am looking at the diagram and it will only lock out the cruise if it has voltage on it. So if you find it, it needs to be hooked up but it would not keep the cruise from working if it wasn't.

Go out to the servo under the hood. It should have a vacuum line going to engine vacuum. It should also have a vacuum line going through the firewall and down under the dash. This is the one that went to the dump valve on the brake pedal.
 
Make sure the VSS is hooked up at the transmission. Speedometer cable comes out and there is a two wire electrical connector there too. Also check for pinched wiring.

If you have a hose feeding the servo from the engine... fun fact if it isn't draped across the brake booster just right the hood hinge will pinch it off. Good times diagnosing that one. It worked fine as far as I could test it but with the hood shut (the only logical way to test it on the road) it wouldn't work.

There is a menu across the top for different things about the speed control system. I snagged a connector from the JY so I could easily test the servo.


The speed control harness:

 

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