confirm I fried my Temp / fuel gauge? - JeepForum.com
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Unread 04-16-2012, 02:48 PM   #1
DDHand
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1977 CJ5 
 
Join Date: Aug 2011
Location: Charleston, SC
Posts: 20
confirm I fried my Temp / fuel gauge?

A. I hate auto electrical.

B. I'm pretty sure i cooked the temp and fuel gauges while troubleshooting a power sending problem ( I think i hooked 12v to the "A" post on the gauge while not paying attention)

C. diagnostics:
Meter testing:,( ignition off, gauge installed, ground connected, all wires disconnected)
Ground to S, I and A terminals show infinite ohms.
S to I shows 20 ohms
I to A shows 0 ohms (0.5 actually)

Continuity light test: (gauges installed, power on)
I to ground - constant bright light
A to ground - constant bright light
S to ground - dim solid light

Operation:
with ignition on :Fuel goes to beyond FULL (after ignition shut off the gauge needle starts to move back to empty after about 8 seconds- seems like a long time??)
Temp does not move.


Any way to tell if I monkeyed up the sending unit as well? A continuity light to the pink wire at the gauge does not light up (ignition on and all other gauge wires ho0ked up).
didnt drop the tank to check the sending unit directly.

This last litte bit of wiring has been more trouble than the entire frame off restoration! 1977 CJ5 v8

Thanks for the feedback

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Unread 04-17-2012, 02:40 AM   #2
John Strenk
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1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 13,007
Putting power to the "A" terminal could mess up the gauge and/or sending unit if left on a long time.
Short time might produce a little smoke but it could still be operational.


It should be:
GRD to S = 71 ohms
GRD to I = 51 ohms
GRD to A = 51 ohms
S to I = 21 ohms
S to A = 21 ohms
I to A =0 ohms

No Ohms to ground is bad.

How sure are you of your ground?

A Continuity light should not be used with the power on. It has it's own power.
Do you mean 12 volt test light perhaps?

Off hand though, it sounds like you burned up the heater on the regulator.

Just use an ohm meter on wire to the sending unit to read the resistance. This shoukld give you an idea if the sensor is screwed or not.
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Unread 04-17-2012, 07:04 PM   #3
DDHand
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1977 CJ5 
 
Join Date: Aug 2011
Location: Charleston, SC
Posts: 20
Thanks John, I used your tutorial to get as far as i did (it was a great help and very well explained for the novice).

I do mean a 12 v light (I gots tools... I just dont know what they do..)

When i say I get an "infinite ohms" reading what I mean is, I get the same reading with the leads connected (ground to S,I and A) as I get with them not touching anything or each other (just to make sure I am using the correct term)

Ohms between the sending wire on the tank and ground show 17 (should be about right for the amount of gas in it)

I did make sure i have good grounds. At least one body bolt in each part was cleaned and connected, good connections from body to frame and engine block. I ran a dedicated ground from the engine block ground to the dash panel for all my gauge grounds (and connected it to the speedo corner bolts)

Thanks again for your input and guide.
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Unread 04-18-2012, 02:10 AM   #4
John Strenk
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1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 13,007
Well if it shows infinite ohms then there is a problem with the regulator in the fuel gauge. That would cause the gauges to go to full then.

You could replace the gauges or possibly add a resistor to the "I" terminal that would cut down on the current through the gauge and get it to work somewhat. I would have to take some current measurements to see what resistor value would work.
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