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Discussion Starter #1
My cruise control will work for several months, and then for a few weeks, it'll die. Yesterday, it died again so I figure it's a good time to troubleshoot it. I have no cruise light, so I can't tell if it's not turning on at all or if it's turning on but not setting. I'd like to make sure it's getting voltage and that the buttons are working, but I don't know what to check. I understand the module is in the driver's side fender. If someone could just let me know which wires should have which voltages or resistances under which circumstances, I could possibly figure this out.

Also, my horn is fried. I was hooking up an airhorn to it [smiles] and my stepbrother was setting up the relay. He put the wires in the wrong places and now the horn doesn't work at all. There is always resistance between the horn wire (the one that plugs into the horn itself) and either negative or positive. The fuse is good, so unfortunately I'm assuming it's a fried wire or horn switch. Any hints on pinpointing the fault? Thanks.
 

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Trumpeter Extraordinaire
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Here's some pinpoint tests from the 1994 Service Manual. You may want to put the OEM horn system back in, in order to test the circuits as listed:

Speed Control Intermittent

Possible Source(s):
Vacuum hoses.
Speed control amplifier.
Speed control servo.
Speed control actuator switch assembly.
Circuit.

Action(s) to Take:
Go to «Pinpoint Test Step A14» .

PINPOINT TEST A: SPEED CONTROL INOPERATIVE

A14 CHECK INTERMITTENT ACTION
Note carefully when intermittent action occurs.
Determine whether intermittent action occurs while cruising or it occurs while using control buttons or turning steering wheel.
Does intermittent action occur while cruising?

Yes
GO to «A15».

No
GO to «A17».

A15 CHECK VACUUM TO SPEED CONTROL SERVO
Check vacuum supply to speed control servo.

NOTE:
8.42 kPa (2.5 in-Hg) is minimum vacuum for normal speed control servo operation. The vacuum source hose is attached to the 7.9mm (5/16 inch) engine vacuum-fitting port.
Is vacuum supply OK?

Yes
GO to «A16».

No
SERVICE vacuum supply.

A16 CHECK SPEED CONTROL SERVO
Separate speed control servo from speed control amplifier.
Connect Circuit 144 (O/Y) lead of the speed control servo to the battery positive terminal.
Connect Circuit 146 (W/PK) lead of the speed control servo to ground, and momentarily touch Circuit 145 (GY/BK) lead of the speed control servo to ground.
The throttle actuator arm should pull in and the engine speed should increase. The arm should hold in that position or slowly release.
When Circuit 146 (W/PK) is removed from ground the throttle actuator should release.
Does speed control servo operate properly?

Yes
SUBSTITUTE known good speed control amplifier if OK -- properly INSTALL amplifier.

No
REPLACE speed control servo assembly.

A17 PERFORM SPEED CONTROL ACTUATOR SWITCH ASSEMBLY TEST
Perform «Speed Control Switch Assembly Test» as outlined (see next post).
Are tests successful?

Yes
SUBSTITUTE known good speed control amplifier if OK -- properly INSTALL speed control amplifier.

No
SERVICE circuits. REPLACE speed control actuator switch assembly or air bag sliding contact as required. Refer to «Section 11-04».



PINPOINT TEST B: HORN SYSTEM INOPERATIVE

B1 CHECK HORN OPERATION
Disconnect both horns as outlined.
Connect one end of a jumper wire to battery positive.
Touch other end to connector at each horn.
Did each horn sound?

Yes
GO to «B2».

No
REPLACE horn or horns that did not sound. RESTORE vehicle. RETEST system.

B2 CHECK HORN CIRCUIT
Using a test lamp, connect lead to a known good ground.
Connect other end to horn harness connector. Position test lamp in visible position.
Actuate horn blow switch.
Did test lamp illuminate?

Yes
System OK. RESTORE vehicle. RETEST system.

No
GO to «B3».

B3 CHECK HORN FEED AT RELAY
Remove horn relay as outlined.
Connect test lamp to known good ground.
Connect test lamp probe to Pin 2, Circuit 1 (DB) at relay.
Actuate horn blow switch.
Did test lamp illuminate?

Yes
GO to «B4».

No
GO to «B5».


B4 CHECK HORN CIRCUIT CONTINUITY
Using ohmmeter, connect one lead to horn harness connector. Connect other lead to Pin 2, Circuit 1 (DB) at relay connector. Read resistance.

Is resistance 5 ohms or less?

Yes
GO to «B5».

No
SERVICE open in Circuit 1 (DB). RESTORE vehicle. RETEST system.

B5 CHECK HORN SYSTEM SUPPLY
Using test lamp connected to a known good ground, connect test lamp probe to Pin 4, Circuit 10 (LG/R) at relay connector.
Did test lamp illuminate?

Yes
GO to «B8».

No
GO to «B6».

B6 CHECK SUPPLY CIRCUIT
With test lamp, check Fuse 16 (20A) at instrument panel.
Is fuse OK?

Yes
SERVICE open in Circuit 10 (LG/R). RESTORE vehicle. RETEST system.

No
GO to «B7».

B7 CHECK FOR SUPPLY SHORT TO GROUND
Using ohmmeter, check continuity from Pin 4, Circuit 10 (LG/R) at relay connector to a known good ground.
Is resistance 5 ohms or less?

Yes
SERVICE short to ground Circuit 10 (LG/R). RESTORE vehicle. RETEST system.

No
GO to «B8».

B8 CHECK HORN RELAY
Reconnect horn relay.
Using test lamp connected to a known good ground, connect probe of test lamp to Pin 3, Circuit 6 (Y/LG).
Did test lamp illuminate?

Yes
Go to «B9».

No
REPLACE relay. RESTORE vehicle. RETEST system.

B9 CHECK HORN SWITCH FEED FOR OPEN
Disconnect battery positive cable as outlined. Wait one minute.
Disconnect driver air bag.
With test lamp connected to a known good ground, check Circuit 6 (Y/LG) at horn switch connector.
Did test lamp illuminate?

Yes
REPLACE horn blow switch. RESTORE vehicle. RETEST system.

No
SERVICE open in Circuit 6 (Y/LG). RESTORE vehicle. RETEST system.
 

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Trumpeter Extraordinaire
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Speed Control Actuator Switch Assembly

Disconnect the 6-pin connector at the speed control amplifier (9D843). Refer to the electrical schematic before performing the following checks.

1. Connect a voltmeter across Circuit 151 (LB/BK) and ground. With ignition switch (11572) in the RUN position, press the ON button and check for battery voltage.

2. Connect an ohmmeter between Circuit 151 (LB/BK) and ground.

3. Rotate the steering wheel (3600) throughout its full range of motion while making the following checks:

a. Press the OFF button and check for a reading between 0 and 1 ohm.

b. Press the SET ACCEL button and check for a reading between 714 and 646 ohms.

c. Press the COAST button and check for a reading between 126 and 114 ohms.

d. Press the RESUME button and check for a reading between 2310 and 2090 ohms.

If resistance values are above the allowable limits, inspect as follows:

1. Disconnect air bag sliding contact (14A664) at the base of steering column tube (3514). Check for battery voltage on Circuit 6 (Y/LG). If there is no battery voltage, go to Step 2, then go to Step 4, otherwise go to Step 4 directly.

2. Disconnect horn relay and bracket (13853). Check for battery voltage at the horn relay connector in Circuit 10 (LG/R). If there is no battery voltage, check 20A fuse and Circuit 10 (LG/R).

3. With the horn relay and bracket disconnected, apply 12V to Pin 4 of the horn relay and bracket. Check for 12V at Pin 2 of the horn relay and bracket. If the voltage at Pin 2 of the horn relay and bracket is not approximately equal to 12V, replace the horn relay and bracket. Refer to «Section 13-06».

4. Disconnect speed control actuator switch (9C888) assembly and measure resistance across each of the air bag sliding contact windings between the air bag sliding contact connector at the base of steering column and the speed control switch assembly connector in the steering wheel. Each resistance reading should be between 0.25-0.5 ohm.

5. Check continuity on Circuit 151 (LB/BK) between speed control actuator switch assembly and speed control amplifier. Check continuity to ground in Circuit 57 (BK).

Reconnect the 6-pin connector at the speed control amplifier.

CAUTION:
Do not use a test lamp to perform the following tests as excessive current draw will damage electronic components inside the speed control amplifier. Use only a voltmeter of 5,000 ohm/volt rating or higher.


On Circuit

Turn ignition switch to RUN and connect a voltmeter between Circuit 296 (P/C) and ground in the 6-pin connector at the speed control amplifier. The voltmeter should read battery voltage. If battery voltage is not present, check the fuse, and service as required. Connect voltmeter between the Circuit 151 (LB/BK) lead and ground in the speed control amplifier 6-pin connector.

The voltmeter should read battery voltage when the ON switch on the steering wheel is pressed and held. If voltage is not available, perform «Speed Control Actuator Switch Assembly Test» . Release the ON button. The voltmeter should read approximately 7.8 volts.

The voltage should remain approximately 7.8 volts until one of the speed control actuator switch assembly buttons is pressed and held. If the meter reads zero, check for ground on the speed control amplifier (either BK wire on the 6-pin connector). If there is no ground on the speed control amplifier, check the system ground connection and wiring. Also check the 20 amp fuse and substitute (but do not install), a known good speed control amplifier, and check for proper ON circuit operation.


OFF Circuit

With the ignition switch in RUN and the voltmeter connected between Circuit 151 (LB/BK) in the 6-pin connector and ground, press and hold the OFF switch on the steering wheel. The voltmeter should indicate 0 volts. If the voltage does not drop to zero, perform «Speed Control Actuator Switch Assembly Test» . If the switches check OK, substitute a known good speed control amplifier and recheck the OFF circuit as outlined.


SET ACCEL Circuit

With the ignition switch in RUN and the voltmeter connected across Circuit 151 (LB/BK) in the 6-pin connector and Circuit 57 (BK) ground, press and hold the SET ACCEL button on steering wheel. Voltmeter should indicate approximately 4.5 volts. Rotate the steering wheel back and forth and watch the voltmeter for fluctuations. If the voltage varies more than 0.5 volt, perform the «Speed Control Actuator Switch Assembly Test» .


COAST Circuit

With the ignition switch in RUN and the voltmeter connected across Circuit 151 (LB/BK) in the 6-pin connector and ground, press and hold the COAST button onsteering wheel. The voltmeter should indicate approximately 1.5 volts.


RESUME Circuit

With the ignition switch in RUN and the voltmeter connected across Circuit 151 (LB/BK) in the 6-pin connector and ground, press and hold the RESUME button on the steering wheel. The voltmeter should read approximately 6.5 volts.

If all the circuits check OK, perform the speed control servo test and substitute a known good speed control amplifier. Do not substitute a good speed control amplifier until the speed control servo test has been successfully completed.
 

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Discussion Starter #4
Whoo hoo! My air horn works. It was the old relay. I had looked in the owner's manual to try to find it before, but there wasn't a relay in that slot. I looked again today and there was. It must have magically gotten there. [whistles] I had my brother press the horn button repeatedly while I looked for a plug on the relay that had voltage when it was pressed. I found it and checked the resistance between the horn output and the other plugs on the relay and when I found one with no resistance, I knew the relay was the problem. I'm using a new relay that came with the horn anyway, so I just cut the horn switch wire and ran it over to the new slot. Blam-o! Thunderbird with an air horn.

As for the cruise control, I'll have to work on it next Thursday when I'm off. How do I know where those circuits are since they go by numbers? Some I can figure out by context clues, but others aren't so clear. Are there schematics for the circuitry? I really have to get one of those cd's. Do they have executables or pdf files or what (to anyone with the cd instead of the book)?
 

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Here's info regarding the speed control amplifier.

Speed Control Amplifier
The speed control amplifier (9D843) is located behind the glove compartment, under the A/C evaporator housing (19850) .

Removal

1. Remove two screws retaining speed control amplifier and speed control amplifier mounting bracket (9D845) assembly to A/C evaporator housing .
2. Disconnect two electrical connectors at speed control amplifier .
3. Remove two bolts and nuts retaining speed control amplifier to speed control amplifier mounting bracket .

Installation

1. Install two bolts and nuts which retain speed control amplifier to speed control amplifier mounting bracket . Tighten to 4-6 Nm (35-53 lb-in).
2. Install two electrical connectors.
3. Install speed control amplifier and speed control amplifier mounting bracket assembly to A/C evaporator housing with two screws and tighten to 1.4-2.4 Nm (12-21 lb-in).

 

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Discussion Starter #6
Domo arigato. I'll work on that tomorrow if I feel like it. The problem is it started working again, so I probably won't feel like it. [smiles]
 
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