I need the location of where to find the tachometer on my 1998 f150 4x4 4.6L

Does the tachometer register when cranking on the engine ?

The speedometer is operated differently then the tachometer. Tachometer
The tachometer displays the engine speed in revolutions per minute (RPM). Voltage pulses are taken from the ignition control module (ICM) (Gasoline) or the generator (Diesel) and sent to the tachometer. Solid state circuits convert the pulse frequency in order to move the pointer of the tachometer.

Tachometer Inoperative (Gas)
Step
Action
Value(s)
Yes
No
1
Did you perform the OBD II System Check been performed?
--
Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check (5.0L/5.7L); Powertrain On Board Diagnostic (OBD) System Check (7.4L)
2
Remove the I/P Cluster.
Disconnect the Ignition Coil connector.
Connect a J 39200 DMM (continuity) between I/P Cluster connector cavity 6 and ground.
Is continuity present?
--
Go to Step 3
Go to Step 4
3
Locate and repair the short to ground in CKT 121 (WHT) between the Ignition Coil and the I/P cluster. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
Refer to Instrument Cluster System Check
--
4
Connect a J 39200 DMM (continuity) from I/P Cluster cavity 6 to ignition coil connector cavity B.
Is continuity present?
--
Go to Step 5
Go to Step 6
5
Replace the I/P Cluster. Refer to Instrument Cluster Replacement .
Is the repair complete?
--
Refer to Instrument Cluster System Check
--
6
Locate and repair the open in CKT 121 (WHT) between the Ignition Coil and the I/P Cluster. Refer to Wiring Repairs in Wiring Systems.
Is the repair complete?
--
Refer to Instrument Cluster System Check

The "cluster" means all of the things you see under the plastic cover in front of the driver, the 'gauges'. The term is a reference to the 'instrument cluster' including speedometer, tachometer, fuel gauge, idiot lights, temperature gauge, everything.
Get a second independent opinion since this is very unusual. Most likely you have a blown fuse.

The Tachometer usually get its drive pulses from the coil. Check the connection of the wires and connecting plugs around the coil. If that doesn't fix it, check the multipin connecting plug on the rear of the instrument panel in the dash.
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Click on the link below to learn how to wire a tachometer to your 1998 Daewoo Lanos

http://www.ehow.com/how_4830244_wire-a-tachometer.html

TACHOMETER IS PROBABLY BROKEN.

Battery Constant 12v+ Positive Wire (+): Black/Orange And Red/White
Battery Constant 12v+ Positive Wire Location: Ignition Switch Harness
Starter Positive Wire (+): Yellow
Starter Positive Wire Location: Ignition Switch Harness
Ignition Positive Wire (+): Blue (16 Gauge)
Ignition Positive Wire Location: Ignition Switch Harness
Second Ignition Positive Wire (+): Yellow/Red
Second Ignition Positive Wire Location: Ignition Switch Harness
Accessory Positive Wire (+): Blue (10 Gauge)
Accessory Positive Wire Location: Ignition Switch Harness
Second Accessory Positive Wire (+): Orange
Second Accessory Positive Wire Location: Ignition Switch Harness
Parking Light Positive Wire (+): Black/Yellow
Parking Light Positive Wire Location: At Headlight Switch
Power Door Lock Positive Wire (+): Orange/Violet
Power Door Lock Positive Wire Location: In Drivers Kick Panel, White 6-Pin
Power Door Unlock Positive Wire (+): Pink/Violet
Power Door Unlock Positive Wire Location: In Drivers Kick Panel, White 12-Pin
Door Trigger Negative Wire (-): Yellow
Door Trigger Negative Wire Location: At Headlight Switch
Domelight Supervision Wire: Use Door Trigger (Requires Relay)
Domelight Supervision Wire Location: N/A
Horn Negative Wire (-): Black/Red
Horn Negative Wire Location: At Steering Column Harness
Tachometer Wire Negative Wire (-): Gray
Tachometer Wire Negative Wire Location: At PCM, Connector 1, Pin A7. The PCM (powertrain control module) is located on the firewall next to the wiper motor.
Brake Light Positive Wire (+): White/Tan
Brake Light Positive Wire Location: At Switch Above Brake Pedal
Factory Alarm Disarm Wire (-): Black/Orange (To disarm requires a (-) negative through a 1565 ohm resistor and an extra relay to connect.)
Factory Alarm Disarm Wire Location: In Drivers Kick Panel, White 12 Pin Plug
Factory Anti-Theft System: N/A
Factory Anti-Theft System Location: N/A

It is definitely the speed sensor assembly which hangs outside the transmission underneath the truck. Usually runs a little over $110

My 1998 Elantra speedometer is also not working.  Before it went, the car seemed to stutter a few times on and off.  I think the speedometer driven gear needs to be replaced but I'm not sure.

IT'S A BLUE WIRE ON THE BACK OF THE CONNECTOR THAT WOULD NORMALLY GO TO THE FACTORY TACHOMETER IN THE DASH. YOU HAVE TO REMOVE THE DASH GAUGE CLUSTER TO GET AT THE CONNECTOR. THE CONNECTOR WILL NOT BE PLUGGED INTO ANYTHING IF YOU DON'T HAVE A FACTORY TACHOMETER (DX, CX, HX ETC...YOU WILL HAVE TO SPLICE INTO OR CUT THE BLUE WIRE FROM THE PLUG. IT GOES TO TACH SIGNAL WIRE ON YOUR NEW TACH.