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Ok, 1990 Bronco 5.0 fresh rebuild. Temp gauge not working. New temp sending units on top of manifold and on pipe riser where heater hose attaches. (Below egr valve) All wires are attached. Temp needle moves from middle of gauge and drops to bottom when I insert key and turn to run. Engine starts and runs fine but needle never moves. I have checked fuses and everything looks good. Ideas? I'm stumped.
Thank you in advance for your input.
 

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The unit that is on the "tee" junction is the coolant temp sensor, and it relays info to the computer, having nothing to do with the gauge.
The smaller one wire unit that is on the manifold behind and to the right of the dizzy (standing in front of the truck) is your temp sending unit for the gauge.
Could just have a bad gauge. Ground the terminal end where it connects to the sender, and your needle should sweep to hot, if it doesnt you either have a bad gauge or damage to the wire. Start there and report back with your findings.
 

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yo Bear,
As Gville advised;
Sender Location pic in a 90 (under rebuild)

Source: by Seattle FSB (SeattleFSB)

Testing; "
Circuit 39 (R/W) and engine ground, using Rotunda NGS Tester 007-00500 or equivalent.
Does circuit resistance read less than 0.1 ohm?
Yes REPLACE engine coolant temperature sender.
No CORRECT engine coolant temperature sender ground connection and RETEST.

Remove the single wire (RED/WHITE) from sender; & ground it & turn the ignition key to RUN. If the needle pegs, replace the sender. If not, diagnose the circuit. by Steve83
 
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