Cruise Control Troubleshooting

[fastpakr]

I'm trying to sort out the problem with the cruise on my '94 Explorer. I've verified that all the secondary components are ok like brake on/off, clutch switch, and dump valve. All vacuum lines are good.

Per the manual I'm reading, I should be getting a constant ~8 volts on the control input wire at the cruise amp. I'm actually getting zero. It goes to 12v when the On button is pressed, but all other buttons are zero. Resistance checks for each switch, however, match the specs in the book. Does anybody know what would be causing this to happen? There's a reference in the manual to checking for a shorted clock spring if this happens on an Aerostar, but no suggestions to the appropriate solution on a Ranger/Explorer.

I tested for continuity between each of the rings at the back of the steering wheel, and none of them are shorted to each other. I do get continuity between the inner and outer terminals coming from the steering column to the wheel, however. Not sure if this is normal or not.

Suggestions from those with experience would be helpful.

 

[locovaca]

I assume you've been to this site, which I consider the holy grail for that era Cruise Control:

http://www.thorssell.net/hbook/ccwire.html

I'm pretty sure that you shouldn't be getting any nominal voltage on the wire, based on that diagram. If I get time later tonight I'll go check out what I'm getting at my amp.

 

[fastpakr]

Thanks - yeah, I've been staring at that website quite a bit. From the drawing I agree - it looks like there should be no nominal power through the control input wire. However, on the same site I find this quote:

The steering wheel switches tell the amp what to do by grounding out the switch line (OFF), putting full to it (ON), or by putting voltage to the amp through resistors (Other functions).

And in my book I find this table:

Control Switch Voltage
No button pressed - 7.8
On - 12
Off - 0
Resume - 6.5
Set-Accel - 4.5
Coast - 1.5

I get 12 on, and 0 in any other state. However, measured at the amp I do get all the correct resistance values according to the following table:

Control Switch Resistance
Off - 0-1ohms
Set-Accel - 646-714
Coast - 114-126
Resume - 2090-2310

And that's where my electrical skills end. Why is no power passing through when buttons (other than On) are pressed, but the resistance tests are fine?

 

[locovaca]

I went out and tested. Those voltages are when the connector is plugged in to the Amp. Unplugged you get the resistances and +12V from On. Plugged in I got:

Nominal - 7.84
On - 12
Off - 0
Resume - 6.4
Set - 4.4
Coast - 1.7

So the nominal voltage must come from the Amp itself.

 

[fastpakr]

You hit the nail on the head - I goofed and missed a couple of lines in the instructions as I flipped back and forth between wiring diagrams and steps. Following the sequence, I've:
1) Checked electrical/vacuum connections
2) Checked horn
3) Checked brake light on/off switch
4) Checked clutch switch
5) Checked actuator cable
6) Checked throttle cable
7) Checked for vacuum at servo
8) Checked vacuum dump valve
9) Checked all controls and switches using resistance and voltage measurements
10) Checked the servo by jumpering it to force it into life
11) Checked speed sensor

At this point, it looks like the only thing left is to swap the amplifier out. Maybe I can find a spare at a nearby yard.

Thanks again for all the help. Hopefully the above steps will help somebody else in the future.