[John Strenk]

Temporarily opened for suggestions..

For a video, go here: https://www.jeepforum.com/forum/f8/quick-gauge-test-4390781/#post40900235

CJ Speedometer Gauge Quick Test

By: John Strenk

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OK, You know what your doing. You don't need a long explanation. Just a test light. Maybe a DVM.

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One Warning. A poor broken ground connection or hooking up the plugs incorrectly can quickly burn up the gauges or sensors. Don't make matters worse. Double check your connections before turning your ignition key to 'ON'
Add a ground wire from the dash to the (-) negative terminal of the battery to be sure.


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Step 1. Start Here

Turn key to ON. Attach your test light clip lead to a good ground.

You may want to disconnect your Ignition coil. These have been known to burn up if the key is 'ON' but the engine is not running.

 

[John Strenk]

Step 2: Power test

Check for power at the "I" terminal.

The test light should glow brightly if you're getting power.

If the light is on go to next step.
If it does not work go to Troubleshooting Section. Check the fuse

 

[John Strenk]

Step 3: Regulator Test

Test for flash at "A" Terminal.

The test light should flash if the regulator is working.

If the test light is flashing go to next step.

If it is not flashing go to Troubleshooting section.

If you are using a DMM then a working regulator should look like this:

 

[John Strenk]

Step 4: Temperature circuit test 1

Remove Temp plug and test for flash at Temp plug:

The light should flash as it did in the previous step.

If the light Flashes go to Testing Temperature sensor. Test 6
If it is not flashing go to Troubleshooting

 

[John Strenk]

Test 5: Fuel Level circuit test 1.

Remove Fuel level plug and test for flash at Fuel Plug:

The light should flash just like it did in the previous step.

If light flashes go to trouble shooting Fuel Level Sensor. Test 7
If it does not flash, go to Troubleshooting

 

[John Strenk]

Test 6: Temperature circuit test 2

Momentarily ground the temperature plug with a jumper wire.

The gauge should go to 'H' in a few seconds.
Don't leave the plug grounded for any longer than necessary.
Remove the jumper wire to ground.

If the gauge goes to 'H' then go to Resistance Tests. Step 8
If the gauge does not move go to Troubleshooting

 

[John Strenk]

Test 7: Fuel Level Circuit test 2

Momentarily ground the Fuel Level plug with a jumper wire.
The gauge should go to 'F' in a few seconds.
Don't leave the plug grounded for any longer than necessary.
Remove the jumper wire to ground.

If the gauge goes to 'F' then go to Resistance Tests. Step 9
If the gauge does not move go to Troubleshooting.

 

[John Strenk]

For the following tests, you will now need an DVM

 

[John Strenk]

Test 8. Resistance measurement Temperature Sensor

Start your jeep and allow it to warm up.

Take your ohmmeter and connect one lead to ground and the other lead to the post on the sensor.

Compare your reading to the following chart:

Temp. Gauge calibration:

Room Temp.....................70 degrees--200 to 400 ohms
C (cold)........................ 130 degrees--73 ohms
Beginning of band........ ..171 degrees--36 ohms
Top of band.................. 242 degrees--13 ohms
H (hot)........................ 270 degrees---9 ohms

These measurements don't have to be exact below 130*F.
Some where in this resistance range though.

Double check the resistance to the base of the detector:

Make sure it's the same resistance as going to the block.

If these reading are OK and your gauges still doesn't work then you need to check your grounds.
Refer to the Trouble shooting section

 

[John Strenk]

Test 9: Resistance test Fuel Level Sender.

Take your ohmmeter and connect one lead to the base and the other lead to the post on the sensor.

Wow, full tank. How unusual.

Also test the resistance to the ground on the frame or better yet, to the dash or back of speedometer. .

As you can see the readings are different, there is something wrong with the ground here.

This will tell you how good is your ground circuit to the tank.

Compare your reading to the following chart

Empty = 73 ohms
1/2 Tank = 23 ohms
Full tank = 10 ohms

Note: If you don't know the fuel level just expect the resistance to be between 73 and 10 ohms. Or fill it up and it should be around 10 ohms.

If these resistance readings are OK and your gauges still doesn't work then you need to check your grounds. Refer to the Trouble shooting section.

 

[John Strenk]

Troubleshooting Step 2

1. Make sure you are on the right terminal. It should be the terminal with the red wire on the right.

2. Check the fuses, on both sides, these older fuse boxes can corrode, weaken etc and not make contact with the fuse.

Newer Fuse Box:

Older Fuse Box:

Both sides of the fuse will light the test light is the fuse is good.

If neither side lights up check if your ignition key is in the "ON" position.

If still not lit then a problem with the ignition switch, fuse box or wiring.

If both sides of the fuse light up and still no power to the "I" terminal, it could be a problem with a bad socket in the fuse box or a broken wire to the gauge.

If one side lights and not the other side then the fuse is blown. Replace the fuse and see if the gauges work now.

>If the fuse is blown, and blows a new fuse, Use an Ohm meter and check resistance from "I" to ground. It should be around 50 (?) ohms.
>If it reads 0 ohms remove the plug from terminal and check the the resistance from "I" to ground again. It should be around 50 (?) ohms .

>If it still reads 0 ohms then you can try to see if the gauge wiggles in it's position. If it does wiggle, it could be the gauge has slipped in the mount and is shorting to the case. You will have to re-center the gauge and tighten the nuts.

>If it still reads 0 ohms then you have a short in your gauge and you will need to remove the gauge to inspect the assembly.

>If the resistance is OK after removing the plug then you have a short in your harness.

 

[John Strenk]

Troubleshooting step 3

What you can check without removing the Speedometer.

1. Ground, Check using test light connect to (+) on battery or a DVM on the Ohms range.
...a. Check ground on dash between (-) on the battery and dash
...b. Check ground on Speedometer housing between housing and dash or (-) on battery.

.......1. Good Ground

...... 2. Bad ground

2. Power
...a. Make sure power connector is still connected.
...b. Touch nut on "I" terminal to see if plug is making good contact with the terminal.

3. Resistance check. Turn power OFF Disconnect all wires on Fuel and Temp gauges

...a. Check resistance from "I" to housing. It should read around 50 ohms

...... 1. If it reads no resistance or infinit then it could be the heater is broken. You would have to replace the gauge.
...... 2. If it reads around 0 ohms, check that the gauge is centered in the housing and is not shorting out. You probably have been replacing fuses at this point.

...b. Check resistance from "A" to housing. It should read around 50 ohms.

...... 1. If it reads no resistance or infinit but "I" to reads 50 ohms then it could be the points are dirty. If you take the speedometer apart, you might be able to clean the points.
...... 2. If it reads around 0 ohms, check that the gauge is centered in the housing and is not shorting out. You probably have been replacing fuses at this point.

...c. Check resistance from "I" to "A". It should read around 0 ohms +0.2 ohms

...... 1.If it does not read around 0 ohms, it could be the points are dirty. If you take the speedometer apart, you might be able to clean the points.

Next step is remove front glass and trim ring of the speedometer housing.

1. Check case of speedometer to case of gauge is 0 ohms.
.... a. If it is not around 0 ohms then the speedometer housing may be rusty and the ground contact on the gauge is not making good contact. Try cleaning up the rust and scrape the contacts on the gauge and test again if the fuel gauge housing is making good contact with the speedometer housing.

 

[John Strenk]

Here is a little video of what you will see:

 

[John Strenk]

This section reserved for troubleshooting step 5

 

[John Strenk]

This section reserved for troubleshooting step 6

 

[John Strenk]

This section reserved for troubleshooting step 7

 

[John Strenk]

This section reserved for troubleshooting step 8

 

[John Strenk]

This section reserved for troubleshooting step 9

 

[John Strenk]

Just a quick post on quick testing gauges.

I'm working on the troubleshooting.

I'll open it up for comments now.

add a link to a detailed PDF later.

 

[John Strenk]

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