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Unread 08-08-2008, 09:26 AM   #1
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1987 YJ Wrangler 
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Fuse and gauges question

1987 4.2L Laredo, 5spd, A/C

I'm trying to troubleshoot an oil pressure gauge that never moves from zero (oh and the clock doesn't work either). All other gauges work fine.

I've ohmed out the sending unit and it reads about 1 ohm with 0 psi. Sprynet says the ohms should be about 234. And I found an old post here on the forums that says you want about 1 ohm with 0 psi. So I'm not exactly sure what it should be.

I tried disconnecting the wire from the sending unit and turning the key on to see if the gauge pegs to the right but it doesn't move.
I also tried grounding the wire that goes to the sending unit and turning the key on and again it never moves.

I checked my fuses and found that the "clock" fuse was blown (well it was the fuse next to the word "clock") so I put a new one in. Clock still doesn't work and the oil pressure gauge is still a no go. Then I found my "dome" fuse blown. Unfortunately I am out of fuses at this time (will have to go get some more after work). Still need to check a few more but I was in a real hurry.

So my question is: Do all the gauges run through one fuse (like "ACC") or through multiple fuses in the fuse block? From the Haynes manual it looks like they all get their power through one fuse which is the "IGN LPS" fuse but it's hard to tell for sure. I really hope the problem is not on the PCB because I don't want to have to pull the dash out.

Any help is appreciated.


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Unread 08-08-2008, 03:33 PM   #2
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1987 YJ Wrangler 
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Not sure if this is the case with your clock but I've bought a couple of clusters for the 87 thru 91 YJ's for various parts. I noticed the printed circuit "wires" leading to both of the clocks were "melted away". Not a lot may be like an inch or two of missing copper foil. Strangely on my current cluster all of the guages work poorly. Gas gauge doesn't all. Oil pressure gauge drops when I turn on the headlights. I have smack the temperature gauge sometimes to get it to read. The clock however works great!
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Unread 08-08-2008, 06:18 PM   #3
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Replace the "dome" fuse. IIRC that sends the 12v to the clock. If you remove the dash plastic overlay around the gauges and htr controls, you'll be able to easily remove the gauge cluster and check the ribbon connector. It's a cheesy setup and you'll probably find corrosion at the least or burnt up ribbons at the worst. Mine has a piece of wire jumping the burnt up feed to my clock. It keeps perfect time. I have the schmatic on the PC if anyone needs it.
I'll just post it:
temp1.gif   temp2.gif  
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Unread 08-08-2008, 06:22 PM   #4
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That's a sweet schematic! I don't need it for myself right now, but it'll be good to have later if I do!

I hope it helps the OP.

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No one here knows what they are talking about. You should try Pirate 4x4 they will be happy to help you.

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Unread 08-09-2008, 04:50 AM   #5
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That's a keeper! Nice job - Thanks
1988 YJ, 2.5 4cyl TBI, 5 Speed, 4WD, 31's. Repaired ECU, Herculined. Wrenchin', scrapin', learnin', paintin', enjoy'n! - The "Work in Progress" …continues into '11! (althought she's been on the road since '08! Enjoy it Dad!)
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Unread 08-09-2008, 04:09 PM   #6
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"Dome" fuse it was!! Thank you! The clock now works.

However, the Oil Pressure gauge is still not working. I'm going to order a new sending unit first to see if that has any effect. It looks like the rusty original one is still on it so I'm sure if it was good it won't be for long. Then if the oil pressure still doesn't move then it's dash time. I may try using a mechanical oil pres gauge just to see if I have any (I'm sure I do).
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