Moss Motors, Ltd

Under a previous post "Fuel Gauge" I apparently entered some wrong information and some readings have changed for some reason. For instance the fuel gauge now reads empty all the time instead of full all the time.  The grn/blk wire from the sender to the gauge reads zero ohms when detached at both ends.  The grn/blk wire reads 5 volts when attached to sender and gauge.  The double green wire reads 12.3 volts when either attached or detached from gauge.  When the sender is removed from the tank with one test lead attached to the body of the sender and the other attached to the post on the sender readings of 10 to 80 ohms occur when the float is raised.  The tank is 1/4 full.      I don't know what the voltage readings are supposed to be and it seems that the new sender is working properly.       Does the fuel gauge need work?       If so instructions on how to disassemble, inspect and repair would be helpful.       I have an 1958 Austin Healey BN6. 

The likely causes for a gauge reading empty all the time are

1) The gauge case is not properly grounded.

2) There is a short to ground in the green/black wire to the sender.

3) The sender has an internal short to ground.

4) There is a broken wire or connection inside the gauge.

5) There is no voltage to the gauge.

It appears that you do have correct voltage so not #5. The resistance of your sender is about right so not #3. If you measured zero ohms on the green/black wire from end-to-end then it is right so not #2. If you measured between one end of the wire and ground then it definately is #2. Assuming that is not the case then that leaves #1 and #4. The more likely of the two is #1. You can do a quick resistance check on the gauge to see if that is it. The resistance between the green wire post and green/black wire post should be about 100 ohms. Between the green and the gauge case, about 50 and between the green/black and the case, about 70. These numbers are approximate. Actually, if you get anywhere near then the gauge is not likely the problem. If any of the above indicate infinite then the gauge is the cause. Good luck.

 

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

Enfoperfect,     The readings I got on the gauge:    Resistance between the grn and grn/blk posts = 700 ohms,    Resistance between the grn post and the gauge case = 760 ohms,    Resistance between the grn/blk post and gauge case = 700 ohms.    Does this shed any light?

Enfoperfect,       On my last reply I must have been looking at the wrong scale.  My ohm readings on the fuel gauge are:
   
   1)  green post /green black post  -  90

   2)  green post /gauge case  -  70

   3)  green and black/gauge case  -  80

You say the  fuel gauge is not likely the problem with readings close to what you quote, which the above are.  But is it possible that if there is a problem with the armature assembly inside the gauge then the fuel gauge arm wouldn’t swing which it should do with a quarter tank of gas.

Possible armature problem but not probable. Electrically, it looks all right. When you hold the gauge in its normal position with no wires attached, try rotating it clockwise. The needle should go from empty to full by gravity. If not then there is definately a mechanical problem. Otherwise, try another electrical test. Reconnect the green wire and the ground but not the green/black. Turn on the key and the needle should indicate full. The gauge must be held in its normal position for these tests, vertical and upright. We will get this sorted eventually.

 

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

Enfoprefect,  Thanks for all your help.  The gauge is now registering properly.  I've learned a lot.  The sender had a poor ground and the gauge had a broken wire which I was able to resolder.  Working with the hair thin wires is definitely a challenge.  Thanks again!!!!!

Glad to hear you got it working. That's kind of an understatement on the tiny wires. I just yesterday had to repair a broken wire and an old solder joint that was not conducting for a Jag XK140. That's probably the same gauge as yours. Might have been easier when I was younger and had numble fingers and actual working eyes.

 

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)