Fuel and temp gage

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Bills70

Bills70

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My fuel and temp gage are not working! I looked at wiring diagram in service manual and it appears that there is a "voltage limiter" that is in that circuit for both gage's! could that be bad and causing my problem, if so, how do I check it if it is? if the limiter is bad will I still have power to the tank? I will check to make sure I have ground at the tank! Also, my tank and sending unit are new, so I am pretty sure it is not the sending unit! Also, if my "Limiter" is bad, does anyone know where I can buy one?
 
There are several threads on this forum about the Limiter and testing gauges.
Perhaps the quickest method is to take a 12v test light and plug it into the slip fit connector for the coolant temp. sensor on the intake manifold or the connector on the gas tank sending unit. Pull the wire connector off the stud and stick the probe inside the connector. You should see the test light pulse ON and OFF. I'm guessing about two times a second.
You can also pull the connector off the stud and jumper wire it to a ground source. (engine block , frame, etc). Do this for a very brief moment and have someone watch the gauges. They should swing towards the Full or Hot range quickly. Disconnect your jumper when this happens so you don't burn out your gauges.
 
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Since both gauges have quit working, the Limiter is very suspect. Although, early Mopars are wired differently. What year vehicle have you got?
 
iScamp said:
There are several threads on this forum about the Limiter and testing gauges.
Perhaps the quickest method is to take a 12v test light and plug it into the slip fit connector for the coolant temp. sensor on the intake manifold or the connector on the gas tank sending unit. Pull the wire connector off the stud and stick the probe inside the connector. You should see the test light pulse ON and OFF. I'm guessing about two times a second.
You can also pull the connector off the stud and jumper wire it to a ground source. (engine block , frame, etc). Do this for a very brief moment and have someone watch the gauges. They should swing towards the Full or Hot range quickly. Disconnect your jumper when this happens so you don't burn out your gauges.
Click to expand...
If I connect the temp sensor wire to ground and the gage "doesn't" works that will mean that the Limiter it bad, correct?
 
That puts it on the high probable list. Could be that power is not getting to the limiter. These units plug into the circuit board and over the years connections go bad.
I don't know off hand if the two gauges share the same fuse.
If you have a test light, that will make for quick analysis of where electrical power is going. I like it better than a multimeter. Just touch some key points on the circuit board.

Since the likely problem is the Limiter, you might want to consider buying a solid state version or making your own. The OEM mechanical limiter can fail in the closed circuit mode (apparently yours failed "open circuit"). If they fail in closed circuit , it will fry your gauges.
 
iScamp said:
That puts it on the high probable list. Could be that power is not getting to the limiter. These units plug into the circuit board and over the years connections go bad.
I don't know off hand if the two gauges share the same fuse.
If you have a test light, that will make for quick analysis of where electrical power is going. I like it better than a multimeter. Just touch some key points on the circuit board.

Since the likely problem is the Limiter, you might want to consider buying a solid state version or making your own. The OEM mechanical limiter can fail in the closed circuit mode (apparently yours failed "open circuit"). If they fail in closed circuit , it will fry your gauges.
Click to expand...
it looks to me that both gauges run off the same
iScamp said:
That puts it on the high probable list. Could be that power is not getting to the limiter. These units plug into the circuit board and over the years connections go bad.
I don't know off hand if the two gauges share the same fuse.
If you have a test light, that will make for quick analysis of where electrical power is going. I like it better than a multimeter. Just touch some key points on the circuit board.

Since the likely problem is the Limiter, you might want to consider buying a solid state version or making your own. The OEM mechanical limiter can fail in the closed circuit mode (apparently yours failed "open circuit"). If they fail in closed circuit , it will fry your gauges.
Click to expand...

Limiter! here is picture of wiring diagram
iScamp said:
That puts it on the high probable list. Could be that power is not getting to the limiter. These units plug into the circuit board and over the years connections go bad.
I don't know off hand if the two gauges share the same fuse.
If you have a test light, that will make for quick analysis of where electrical power is going. I like it better than a multimeter. Just touch some key points on the circuit board.

Since the likely problem is the Limiter, you might want to consider buying a solid state version or making your own. The OEM mechanical limiter can fail in the closed circuit mode (apparently yours failed "open circuit"). If they fail in closed circuit , it will fry your gauges.
Click to expand...
where do I buy a solid state version Limiter?

DSC00253.JPG


DSC00252.JPG
 
If I recall correctly, the fuel and coolant temp. gauge use the same plug-in limiter. And you have a Red light for oil pressure?
Of course , check the fuse, I think it is for just those 2 gauges.
Do the dash panel lights work? It's a different fuse but, I think it's just one large connector to supply all the gauges and lights. Plugs into the circuit board.

Access is not easy with the instrument panel installed but if you can lay under the dash and probe the 12v input to the Limiter and the pulsating output with a light that will confirm the problem. (without shorting anything out).
An analog voltmeter will show about 5v output. Not sure what an electronic digital meter will show. The display may be erratic??
Just in case you don't know. The Limiter takes 12 volt input, and an internal mechanical contacts open and close rapidly. 12v-0v-12v-0v........ The result is a nominal 5v that the gauges "see".
 
In the diagram, just to the left of the limiter is the multi pin connector. The connections there can go bad. You lose all your gauges and panel lights.

Panel grounds often go bad. But, if you can probe the circuit board where your diagram shows 5v and 12v , you will have your answer right away.

Solid state limiters are available on Ebay. They are about $40 to $50 dollars. Not cheap but, they do have a fail safe mode to protect the gauges. There are other sources on line.
 
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