Join Date: May 2011
Location: Elbert, CO
Compliments to JeepHammer....
Troubleshooting Guide For '78 to '86 Jeep CJ Vehicles.
1. Aquire a 'Test Light'.
If you purchase one (thet run between $6 & $12 at parts/tool stores)
Look for the type that has a light bulb, (NOT an LED Type).
Most test lights look like an ice pick with a bulb in the handle and a wire coming out of the 'Ice Pick'.
2. Testing the test light.
Once connected to the battery, you will 'Probe' the other battery terminal to see if the light works or is burned out.
3. Since there are so many components in the ignition stystem, Fuses, Switches, Tachs, a dozen connectors, ect.
It's VERY IMPORTANT to find a starting point to trace you 'Issues'.
The easisst place to do this is at the Ignition Coil Connector.
The coil connector will tell you if the 'Issue' is with the interior wiring (Ignition Swtich, Ignition Fuse, Factory Tach, Firewall Connector, Ect.)
Or with the Ignition system in the engine bay of the vehicle...
Since the system 'Splits' at the ignition coil connector, this is a good place to start with testing.
4. The Jeep/Motorcraft ignition has TWO ignition circuits,
One is the 'Starting' or 'Cranking' circuit, When the ignition switch is in the 'Start' position you are powering the coil/igntion module from different circuits than you would be if the Ignition switch was in the 'Run' position.
Testing might seem redundant, but you need to test BOTH of the ignition circuits to make sure things are working correctly, so DO NOT skip any steps
5. Since you will be working with LIVE WIRES,and you will need to crank the engine,
MAKE SURE your transmission is in 'Park' or 'Neutral' and the
parking brake is set or the wheels are chalked before you do this testing.
SAFETY GLASSES are always a 'MUST', and since you will be working under the hood around moving parts, belts, pulleys, ect. make SURE your cloths, hair, jewlery are secured so they don't get into moving parts.
I can not, and will not be responsible for your safety, and there is no way I can list all the safety issues you will need to address,
So if you are not comfortable with working around moving parts, DO NOT proceed!
Connect the test light wire to the NEGATIVE battery terminal.
(Probe the positive battery terminal to make sure the light works)
Remove the ignition coil connector from the ignition coil.
We WILL NOT be testing on the coil, just the wires in the connector.
Turn the ignition switch to the 'Run' position.
Probe the 'Red Wire' terminal in the coil connector, you *SHOULD* see the tester light up.
--*IF* you DO NOT get a 'Light' when you probe the 'Red Wire' terminal in the coil connector,
Your 'Issue' is most likey INSDIE the cab of the vehicle,
Ignition Fuse, Ignition Switch, Key Switch or activation rod, Factory Tach, or connections.
--*IF* your test light does light up,
Then proceed to next test.
Have someone turn the key switch to the 'Start' or 'Crank' position and see if you have a 'Bright Light' while the engine is cranking.
WARNING, The engine IS going to crank (will not start, but will crank).
--*IF* you DO NOT have the tester light up, then you have a broken 'Red' wire from the small 'I' terminal on the starter relay ('Solenoid') to the coil
connector 'Red' wire terminal.
--*IF* you DO have the tester light up, then proceed to next.
Move the wire on the tester to the POSITIVE battery terminal.
With the key switch in the 'Run' position, Probe the 'Green' coil connector terminal.
You *SHOULD* see the tester light up.
--*IF* the tester DOES NOT light up, you have one of two issues,
The 'Green' wire is not making connection with the Ignition Module,
The Ignition Module isn't being 'Grounded' through it's 'Black' wire to the distributor housing.
--*IF* The tester DOES light up, then you have VERIFIED the 'Ground' path from Coil Connector to the Module, and from the Module to the 'Ground' at the distributor.
(This will be important later on...)
While probing the coil connector 'Green' wire, have someone turn the key switch to the 'Start' or 'Cranking' position.
You *SHOULD* have a 'Flashing' test light while the engine is cranking.
--*IF* you DO NOT have a 'Flashing' tester, then the Module isn't firing the coil like it's supposed to.
--*IF* you DO have a flashing tester, then move to next.
Leave the coil DISCONNECTED for now, and move to the MODULE CONNECTIONS.
You will find your ignition module on the drivers side fender, under the washer tank, on the back side of the fender.
It will have a 2 wire connector (Red & White), and a 4 wire connector (Orange, Violet, Green & Black), is about 6 inches square and about two inches
thick aluminum box.
Disconnect the two wire connector (Red & White wires from the module),
The wires will be Red & Blue on the harness (Engine) side of the harness, and that is were you will be testing.
'Ground' your test light to base metal, like the engine block,
Then probe the 'Red' wire in the HARNESS side of the connector.
You *SHOULD* get a light from the tester.
--*IF* you DO NOT get a light from the 'Red' wire on the harness side of the connector, then you have a broken wire from the 'Splice'.
The ignition circuit comes through the firewall connector, splits into three wires, and the split point is where the 'Splice' is.
One wire will feed the module ('Red in the module connector),
One wire will feed the ignition coil through a resistor wire (Red to the ignition coil)
And one will feed the 'Excite' terminal to the alterantor.
If you get power to the ignition coil with the ignition switch in the 'Run' position, and you DO NOT get power to the module connector, then you have a bad
splice or you have a bad wire from the splice to the connector for the module.
--*IF* you do get power at the 'Red' wire on the harness side of the module,
Then move to next test.
Probe the 'Blue' wire going into the module/harness connector while someone is cranking the engine.
If you get the tester to light up, then you are getting power to the module 'White' wire and that's what it's supposed to do.
--*IF* you DO NOT get power to that 'White' wire during cranking of the engine,
You have an issue with the wiring splice for that circuit or you have a broken wire from the splice to the connector.
The 'Blue' wire comes from the bulk head connector, splits (Splices) into two wires,
One to the starter relay ('Solenoid') 'S' terminal (so if your engine crankks, the ignition switch, fire wall connector, ect. is working),
And one side of that splice goes to the module 'White' wire. If engine is cranking and you don't have power to that 'White' wire, the module side of that splice has issues.
--*IF* you get the tester to 'Light' up, then you move to next test.
Unplug the 4 wire connector from harness to module. You will be testing the HARNESS or ENGINE side of the connection.
IF YOU DID THIS BY THE NUMBERS SO FAR, the 'Ground' connections were tested when you tested from the ignition coil terminals,
YOu can move directly to the distributor trigger testing...
'78 to '81 Jeeps,
Use a 'Multimeter' set to 'Ohms' (about $15 from Wal-Mart) on the Violet & Orange wires in the 4 wire connector (Harness side).
You should show about 625 Ohms, but 400 to 800 Ohms is acceptable.
('Ohms' is a measure of electrical resistance. It's also expressed as 'Ω' on some multimeters)
'82 to '86 Jeeps will NOT have a 'Violet' wire going into the harness side of the connector.
Test at the distributor connector, distributor side of the connector, again, test the 'Orange' & 'Violet' wires for resistance in the connector.
--*IF* you DO NOT get a reading (Broken Connection/Wire) then you have a connector or harness problem, or you have an open 'Stator' ('Trigger' in the distributor with a broken wire).
--*IF* you get the proper Ohms reading of around 626 Ohms, then your distributor trigger is working and you probably won't need to chase that circuit any further.
Move to the next round of conclusions and remidies...
DO NOT FORGET TO HOOK THE COIL, MODULE & DISTRIBUTOR CONNECTORS BACK UP!
You feel pretty stupid when you find a bad component, replace it, and the vehicle won't start...
Because you forgot to hook the coil back up!
(Ask me how I know that!)
99 times out of 100, when the coil is getting power when it's supposed to, the module has given up.
The DuraSpark module used in the '78 to '86 Jeeps is pretty weak, and the 'Import' versions we've been forced to use for years is disgraceful...
If you coil is NOT getting power when the key switch is in the 'Run' position,
Then check the module 'Red' wire.
If it's not getting power, then you probably have a bad fuse, ignition swtich, key tumbler, ect.
If you ARE getting power to the module and coil, 99/100 bet it's the module.
Occasionally, the trigger in the distributor, called the 'Stator', goes bad.
This is VERY easy to diagnose with a multimeter.
Around 625 Ohms or change it out.
I change mine out about every 5 years or so no matter what, the old one goes in the 'Spare Parts' box if it was still working.
Better safe than sorry and stranded 15 miles out in the boonies!
If everything else tests out fine, then the coil is probably your issue.
Coils can be checked with a multimeter, but since virtually no one has a factory coil on their engines after 25 or 35 years, it does me absloutely no good to tell you what to look for on a factory coil since none of us have them any longer.
If everything else checks out, then change the ignition coil and see what happens...
They aren't expensive, easy to change, and couldn't hurt anything even if it wasn't the primary 'Issue'.
If you don't get power to the engine compartment,
Try reaching up on top of your steering column under the dash, at about 11:00 O'clock, and feel for a rod that connects the key cylinder to the ignition switch on top the steering column just inside the firewall.
Sometimes that key switch linkage gives up, especally with tilt steering wheel columns, and mimics a bad ignition or ignition switch when it's actually a linkage problem.
By locating and 'Helping' that rod move up and down the column as the key cylinder is turned, you may find out it's a linkage issue...
DO NOT FORGET!
Bad coil wires, bad rotor or center button in the distributor cap, ect. will mimmic a bad ignition.
Make sure you have coil wires, caps, rotors changed regularly so you don't chase a bad 'Ignition' in the wrong place!
One more thing to remember,
The Jeep/Motorcraft ignition WILL BURN UP THE MODULE if you leave the key switch 'On' without the engine running!
If you need to run the radio, wipers, ect. with the engine 'Off', then turn the key switch BACKWARDS to the 'Accessory' position so the ignition isn't cooking it's self.
This is just a quirk of the Jeep/Motorcraft ignition system, so remember NOT to leave the key in the 'Run' position when the engine is NOT running.