OK, I have been chasing gremlins on this thing. I replaced the sending unit with the one from Ecklers....replaced the gauge from ZIP and STILL I cannot make the gauge read correctly. I checked the OHMs on the sending unit...OK I checked the connector at the gauge....Power...OK Ground...OK Continutiy on the wire from the sending unit to the connector...OK.

Read all the posts re: Resistor, Sending unit, and Temp Gauge and still I'm a little confused. I still have the original sending unit, checked the OHMs...cold = 768 and hot (placed in 200*water for 10 minutes)=150...so maybe the old stock sending unit is still good.

Two Questions: Could the new sending unit NOT be matched with the rebuilt stock temp gauge? Do I need to swap with the old stock sending unit?

AND 2: How the heck should the back of the gauge look? Did I replace the connectors correctly? As you are looking at the back of the gauge....the "flat wire-wrapped" thingy is horizontal on the 3 o'clock and 9 o'clock posts. Is there any insulated washers (nylon) between the"flat wire-wrapped" thingy and the gauge housing or not. The resistor, which is the stock one, is vertical on the 12 o'clock and 6 o'clock position...are there ANY insulated washers anywhere?

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ttt

 

Does this picture help (I think the one on the lower right is temp gage)? You will need to trace the wires to see if one is bad, do you have the wiring schmatic?
The colors are Pink, Black and Dark Green. Black is the ground, make sure it is grounded. Dark green goes to the sending unit (through the bulkhead connector), and pink is the hot lead (looks like it goes to the fuel gage as well). I'm looking at the wiring diagram for my 71', but it should be simular to your 75'.

 

 

Don't know as I have since put the thing back together. Picture was from a couple years ago.

 

Vetteguy the insulated washer goes under the "flat wire-wrapped" thingy--between the thingy and the housing
Also the center male connector on the other end of the thingy goes under the thingy next to the housing.There is a hole in the housing for the tab on the connector.
When I say housing I mean the entire back of the cluster.Has the different wire colors printed on it.
You do realize the housing goes in between what you have in the picture -right?edit-ok I'm sure you do-you can see it on Dukes post.

 

OK, I think I understand about the center connector...with the gauge facing down and the top post is at the 12 o'clock position, here is the "order" of the center connector.

1) Gauge Cluster backing (blue) with the post poking through, then the...
2) Center male connector (with the bent tab in the alignment hole) then the...
3) Insulated washer? then...
4) The "wire-wrapped" thingy and finally...the
5) lock washer and nut.

Is the insulated washer in the right place?

Thanks!

Stuart

 

I chased a similar problem with my 71. It turned out the original sensor was the best solution. I was surprised but that was the simple solution.

 

Funny spotting a thread NOW about this....I have been playing with my '72 gauge here because I forgot to get the replacemet heads redrilled for the old large sending unit....so AZone got me a gauge from Ford trucks that did screw into the aluminum 113 L98 castings...but problem is....of course the resistance range is differant....so I had to add 50 ohms in series, and ~1000? I forget across the gauge....and that seemed to pull it somewhat into line....what needs doing is take that thing all apart and redo the entire network...but it's a thing of NEED vs TIME, Desire.....it's good enough in the critical areas....

 

Vetteguy-thats NO on your post #7
In this pic on this post -the washer goes just where the arrow is pointing -under the wire thingy
Now the opposite post is where the center male spade with the tab goes under the wire thingy.
This pic is correct.

 

THANKS!!!!!! Right now I'm getting NO reading from my gauge....after checking EVERYTHING...which tells me I'm not getting a good ground....

 

Do you mean the needle is just below 100* ? That usually means you have 12 volts and the ground -and now all you need is input from the temp. sender at the motor.