My temp gauge max out put new sending unit in did not fix is there more than one??? also my oil pressure gauge sarted acting up work fine before now it drops to nothing and light comes on when you first start it it will start coming up then drop to nothing this is on a ford f150 4 wheel drive with a 4.6
SOURCE: 1989 Ford F150 Instrument Cluster Problem
Some of the gauges are on the same fuse as the dome light; check the fuses. The other main source of gauge problems for this vintage F150 is the sending units and I don't use the term sending unit lightly, so when you go to the parts store make sure you say you are looking for sending units not sensors (sensors hook to the computer) sending units are of 2 types for this vintage F150, lights and guages you need the ones for gauges, the oil sending unit is about 4 dollars and the coolant temp sending unit for a guage is about the same.
I have 4 fords and you will come to understand that the wiring is a jury rig, all this come out when they are the age of your 1989 PU.
SOURCE: check gauges light on f150
first check to see if battery fully charged and if it isn't put it on a charger and if the truck takes a jump and you can get it running while it is running take the positive side of the battery cable off and if it dies then it could be the alternator if it doesn't die then it could be the drive belt because if the belt is slipping that will also cause the battery to loose charge and the truck will not start
SOURCE: heat fluctuation on temp gauge
change the sending unit to the fan, if that doesnt work check for power too the fan or even a bad fan
SOURCE: oil pressure problem
You oil pressure sending unit has gone bad, it's common to go bad and some even leak oil.
The oil pressure sensor is on the back of the block on the passenger side, you can get to it from the top and not from the bottom. There are (2) switches back there that screw in to the block and you can only see it from the top of the engine. The Oil Pressure Sending Unit is the one wire harness with a green and white strip on it. The other switch has more wires to it.
When you pick up the new sensor, make sure you get the right one. make sure you get the Oil Pressure Sending Unit which sends variable oil pressure and has only one quick connect for the wire connector. The oil pressure switch is the one that only activates the oil light on older engine.
Once you get the right part at Auto Zone for around $9.00, disconnect the wire clip with the green with white strip on it. and use a deep spark plug socket with a extension and u joint to get the sensor out. The sensor comes with teflon tape already and no oil should leak out from the block. It as simple as replacing a bolt and reconnecting the wire connector.
Good luck and hope this helps, take no more then 10 min to do but about 5 hours for the engine to cool off LOL
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