Got you 2 diagrams.
Follow the yellow/ green wire-it goes from the temp switch to the gauge
you may have squished it
it may have rubbed thru the insulation and now is touching "ground"
maybe you tied some other accessory into it
something under the dash may be grounding the gauge
all of the above would mean the wire is grounded-especially if the second you turn the key on it rises to the top
(just some useless info as a test, grounding "sender wires" such as to the fuel or temp gauge let's me/ us/ anybody know if the gauge or the sender is bad)--yours seems to be testing itself!
Other than that---maybe a defective sender or a bad gauge
to "verify" the wire may be grounded you can take it loose at the gauge and see if it drops
with the key on - if there are "connectors" on the way to the sender, disconnecting them---as you progress, may make the gauge drop and sorta let you know which way on the wire that the problem is
extreme case with no connectors (key on)---find an ez to fix place on the wire and cut that puppy!---Does the gauge drop or not?--Investigate the wire further on if it did drop
my last pic-"willy's" fuel tank sender - although my float is "up" and my gauge is on full - this is exactly what would happen if I "grounded" the sender wire anywhere along the wire from the sending unit all the way to the gauge - in fact - I could ground the "stud" that the sender wire connects to on the gauge itself and the gauge would peg out
lemme know if this helps
Images (Click to enlarge)
Thursday, April 24th, 2014 AT 8:08 PM