2 electrical gremlins for 84 CJ - JeepForum.com
 
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post #1 of 8 Old 08-22-2017, 10:33 PM Thread Starter
carpesdiem
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1984 CJ7 
 
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Unhappy 2 electrical gremlins for 84 CJ

Need help please diagnosing 2 electrical gremlins.

#1 I was getting wacky readings from my oil sending unit so replaced with correct new one. Now it seems i have only 2 resistance settings from sending unit. (Slight engine revs 35-48 OHM i.e. 80 psi) or infinity (open). Needle of course when hooked up swings back and forth? resistance measured at sending unit with lead off?

#2 Dash Light don't work. EVERYTHING else does. Fuse that controls taillights is fine if there is NO dash fuse plugged in. As soon as I plug in dash light fuse.. tail light fuse pops and still no dash lights but the dash light fuse is fine??

Thanks for the ideas in advance... Id give you more history on the Jeep but I just got it with little history..However it is in great shape and runs well.


Jeeps and motorcycles..is there anything else?
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post #2 of 8 Old 08-23-2017, 03:11 AM
BagusJeep
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Dash lights and fuses are wired as follows:
Attached Images
 

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1981 CJ7 258ci - Bagusjeep
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1981 J20 258ci - Gladys
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post #3 of 8 Old 08-23-2017, 03:19 AM
BagusJeep
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The ACC LPS fuse is for the panel lamps and is fed by the rheostat in the light switch which gets power direct from the battery.

The tail lamps are on a seperate circuit, the PARK TAIL fuse is seperate. It does however pass through another part of the light switch.

The only place they cross paths is at the light switch.

I suggest you have a look at how the light switch is wired. In particular that the circuits are entirely seperate. If the tail light feed also fed the panel lamps due to some PO rewiring, then the additional load of the panel lamps may blow the tail light fuse but not the panel lamps (if everything on the panel was fine, it would not blow the downstream fuse). A bodge would be to increase the PARK TAIL fuse rating by 5 Amps, not advisable.

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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
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post #4 of 8 Old 08-23-2017, 10:26 PM Thread Starter
carpesdiem
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Quote:
Originally Posted by BagusJeep View Post
The ACC LPS fuse is for the panel lamps and is fed by the rheostat in the light switch which gets power direct from the battery.

The tail lamps are on a seperate circuit, the PARK TAIL fuse is seperate. It does however pass through another part of the light switch.

The only place they cross paths is at the light switch.

I suggest you have a look at how the light switch is wired. In particular that the circuits are entirely seperate. If the tail light feed also fed the panel lamps due to some PO rewiring, then the additional load of the panel lamps may blow the tail light fuse but not the panel lamps (if everything on the panel was fine, it would not blow the downstream fuse). A bodge would be to increase the PARK TAIL fuse rating by 5 Amps, not advisable.
So for clarification:

Either someone crossed wires somewhere between tailight and dash/ gauge lights OR..

My headlight switch may be bad and they are crossed there.

Since my dash wires look like everyone elses (probably a rats nest ) Would you recommend as a first step to to replace the light switch?


Also any ideas on my oil pressure sending unit? Thanks again for the help
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post #5 of 8 Old 08-23-2017, 11:21 PM
BagusJeep
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Changing the switch may not help you. The problem may be in how the wires are routed to it. I suggest unfastening from the dash, drop it down and having a good look at how it is wired, trace the two circuits and make sure they are not combined in some way.

You could try to disconnect the wires from the switch and jumper the wires together to complete the two circuits. If the fuse is still blowing, not the switch.

A rat's nest is very common, room for lots of PO bodges. You will need to trace the power with a 12V test bulb or similair back from the switch to the fuse box etc

As to your oil pressure sending unit, if your measurements are accurate it is broken. It is definetely a sender and not a switch? Are you measuring between the sender terminal and engine block? Have you put PTFE tape on the threads?

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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
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post #6 of 8 Old 08-24-2017, 03:25 AM
ECJ-7
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sounds like you bought the oil pressure sender for an idiot light, not a gauge.
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post #7 of 8 Old 08-24-2017, 04:02 AM
John Strenk
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I can see this happening to the light switch that would blow the tail light fuse and not the dash light fuse:

{ing]http://civilianjeep.info/Strenk/Lights/HeadLightSwitchShortToGroundConnection.jpg[/img]

Caused by the rheostat falling out of position.


Causing the rheostat to short out against the ground tab for the dome light.


This is because the short takes place BEFORE the dash light fuse so it will never blow. Although it is odd that it blows after inserting the dash light fuse. it should blow as soon as you turn the lights on.

I agree with ECJ-7. Either you got an oil pressure switch for a warning light or wrong/faulty pressure sensor.
There were two pressure sensors for the CJ one for low ohms and one with higher ohms.


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post #8 of 8 Old 08-25-2017, 11:06 AM Thread Starter
carpesdiem
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Thank you guys for the help. Ive replaced twice the oil sending unit part #3212004. What is the number of the other sending unit please??

(To be clear it works and just oscillates at idle from open circuit to 35ohm when i push the gas nothing in between) Could that mean i need the lower pressure unit?)
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