98 ranger 3.0 2wd. Temp gauge isn't working. First I grounded out the single wire and the dash pegged to hot so I replaced the temp sender. Still didn't work, so then I replaced the thermostat. Still didn't work. I did have a heater issue but that turned out to be a clogged heater core so I fixed that and heat works fine now. When I watch the live data on my scanner it show my ECT building to about 190° then drops so I know my thermostat is working and I know my ECT sensor is working. Is it just a bad dash? Everything else on the dash works. Could it be a bad dash even though I ground out the sender wire and the dash needle pegged to hot?

Also I should state that I tested the new sender by making sure it's properly grounding the body of the sender to the engine with my voltmeter. And I makes sure the plug was good by testing the prong on the sender to the wire with my voltmeter.

 

Welcome to the forum

1998 temp sender may have 2 wires, red/white to dash gauge, and a Black/white wire as its Ground
Do that test again but use the black/white wire as the ground to make sure gauge goes to HOT, if not then need to re-ground that black/white wire

Temp sender is a 12volt unit, low OHMs, 150ohms cold, 26ohms center line on gauge
ECT sensor is a 5volt unit, high OHMs, 38k ohms cold, 3k ohms center line
Make sure someone didn't sell you an ECT sensor instead of a Temp Sender

 

I specifically asked for the sender not the sensor from the auto parts store, that's not to say they didn't give me the wrong part. The sender only has one wire going to it. Is it supposed to have 2 wires(positive and ground)? I can include a pic of the old sender(it looks the same as the new)

 

The sender is the new one with only one wire and the sensor is to the right of the thermostat correct?
Also I'm only getting 10.72volts from the single wire.
The alternator is charging the battery at 14.2v

 

Yes, if threads had a metal Ground to engine then the 1 wire will work, and inside the sender there is only 1 contact, correct?
If there were 2 contacts inside the sender then it needs an external ground wire, or its an ECT sensor, they always have 2 contacts/wires

Try this, unplug the sender and use a jumper wire from red/white wire to metal part of the sender(the ground) and see if gauge goes to HOT, it should of course
If not then sender threads have a bad ground, the lower threads on these need to be bare metal to get a good ground, and because its on a screw in elbow those threads also need bare metal to ground to the lower intake manifold

If gauge goes to HOT, then new sender is bad, use OHM meter to test ohms between contact and metal part of sender, should see under 200ohms


The ECT sensor should be on the lower intake(like in the picture) since its more important to engine operation that the temp sender
But their positions/threads are interchangeable if the wires reach, lol

If the gauge goes all the way up to HOT when you do the red/white wire to Ground test then Voltage is OK, never tested the voltage on that wire but it would have to be lower than battery voltage to prevent a Dead Short if that wire ever shorted to ground in the harness, so there is built in resistance in that circuit

 

with a jumper wire from the harness to the ground it pegs the temp gauge to hot.... the new sender has 2 posts in the plug. im wondering if they sold me a sensor and not a sender. and if thats the case this is the exact reason all part stores need to train their people better. ill try running a jumper from the harness to the sender and from (what i assume is) the negative of the sender to a ground and see if that changes anything.

 

Its most likely the wrong sender, in the mid to late 1990's Ford was using plastic intake parts which of course are not able to be grounds, so senders needed to be 2 contact versions

Looking at wiring diagrams 1998 used 1 wire sender, but 1999 and up used 2 wire sender
Maybe ask for a 1996 or 1997 temp sender, should be same connector but only 1 contact

Worst case is you get the 2 wire connector and add the ground wire, you can buy 2 wire connectors for senders