84 B2 2.8L swap to 92 4.0L - transmission and wiring questions

[Bronson with Bronco]

I spent time this weekend trying to get gauges working in the dash. I'm wanting to keep all of the original gauges in my 84 Bronco II. I installed the oil pressure sensor from my 2.8L into the 4.0L, so that one was pretty easy (though it's only working intermittently). However, I'm not getting anything on my engine temp or ammeter.

Does the 4.0 also use a switch for the temp instead of a sensor? Would the solution be to install the sensor from the 2.8?

What about the ammeter? The charging system is working, just not the gauge. Not sure where to start with this one.

 

[franklin2]

Did the ammeter ever work? They usually do not give much indication even when they are working. If you are using the original alternator and alternator wiring, it should work. If you are using the 4.0 alternator and it's wiring, the ammeter is not going to work.

On the temp sensor, first find the correct wire out in the engine bay. Turn the key to run, and then ground and unground the temp sensor wire to the engine block. The temp gauge should swing cold to hot when you do this(give it a little time, they are slow). If it passes this test, the gauge and the wiring are good, I would go ahead and swap sensors. Make sure you use little to no sealer or thread tape on the sensor, it needs a good ground to the block to work correctly.

 

[Bronson with Bronco]

Thanks, @franklin2.

The ammeter did work with the 2.8L. I'm using the 4.0L alternator and wiring. Is there a way to get this working?

Will the 4.0L temp sensor/switch work with the 84 gauge?

 

[franklin2]

The later model ranger gauges worked differently, Ford changed things around. So the later sensor probably will not work, different ohms.

What amp output does the later alternator have? If it's a lot higher than the older alternator, it would not be a good idea to try and make the old ammeter work, the wiring for it may not be large enough (the shunt).

If you can find the old alternator wiring, find the wire that went to the alternator output (the fatter wire). Follow this from the old alternator connection, it will go across the engine to the driver's side where it meets up with a larger wire that went around the radiator to the battery. Somewhere in this larger wiring you will find a strange looking piece in the wire with a smaller wire spliced in on each side. This is the shunt. It's a very very small resistance. The small resistance creates a small voltage drop when amperage is flowing through it. These small wires on either side of the shunt went directly to the dash ammeter, which is really a very sensitive voltmeter. The ammeter would read this small voltage generated by the shunt.

 

[franklin2]

P.S. The smaller wires on either side of the shunt that go to the ammeter are a red/orange wire and a yellow/lightgreen wire.