Manually testing via the 14 pin connector is not hard but it can be tedious. To help others trouble shoot problems with their cruise control, I have prepared the following tutorial on testing the cruise control system. Note that this is based on an 89 GW. Your FSJ system may be different but the principles are the same. Refer to the wiring diagrams in your FSJ to help work out any difference.
For starters, let’s take a quick look at the main components in the system.
1) Control module – circuit card in a yellow box under dash. My yellow box was under dash next to left foot of passenger. This testing does not test the module. It tests everything BUT the module. If everything else test OK then that implies that the module is bad.
2) Multi-function lever on steering column – inputs commands to system for setting and adjusting speeds
3) Brake control switch – mounted above the brake petal. It is an open circuit until you hit the brakes then it allows 12VDC to flow to the module on pin 13. The module monitors pin 13 to know when you applied brakes so it can turn cruise off when you apply the brakes
4) Inline 4 amp glass fuse that feeds 12VDC to the multi-function lever. I think it is a slow blow fuse but not sure. If blown, nothing will work. Impacts reading on pins 5, 10 and 14. This fuse is buried deep under dash and very difficult to get to.
5) Speed sensor – sensor mounted to transmission and lets module know your speed. Inputs to the module via pins 2 and 3. Voltage readings are AC (not DC). That tells me that the sensor is a small motor (generator) that generates a variable VAC depending on speed.
6) Control servo – Mounted on driver side fender under hood. Uses vacuum and signals from cruise module to control gas to carburetor. Linked to cruise module via pins 4, 6, 11 and 12
7) Fuse panel – mid left side of panel has a slot (marked for cruise control) to plug the cruise control power wire into. The plug gets it power from the yellow 20 amp HAZ/STOP fuse. This power wire goes to pin 7 in the 14 pin connector
8) Ignition key – position of ignition key is important in the testing since the cruise control system is like an accessory and only works when key is in RUN position
9) Connectors and connections – even if all components are good, a bad connection is very possible and will cause bad or erratic readings. Always tough to track down the specific bad spot.
Recap of the 14 pins in the connector shown below. Pins numbered 1-14 from left to right.
1 – Ground wire
2 – Speed sensor and Cruise control servo
3 – Speed sensor
4 – Cruise control servo
5 –Multi-function lever
6 - Cruise control servo
7 – 12VDC from fuse box
8 – Unused
9 – Unused
10 - Multi-function lever
11 - Cruise control servo
12 - Cruise control servo
13 – Brake switch
14 - Multi-function lever
The following test are grouped by type of test. All tests are done with a simple VOM meter that can measure ohms, VDC and VAC. These tests are electrical in nature only. Does not test your vacuum (must be OK for control servo to function) and the linkage to the carb (properly adjusted). All these test will do is point you to the circuit that has a problem. You will probably need to do addition testing to isolate the problem in a bad circuit.
2004 4.8LS/Advance Adapter/727/242 D44/AMC20 Serehill tailgate and headlight harnesses 
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