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Minor Problems After Engine Swap

I have a 1994 Nissan Hardbody truck. 2.4L 4cyl engine with 5spd transmission. This is the 4x4 model.

I had to replace the engine and transmission at 180k miles. I purchased a wrecked vehicle for the parts because it had very low mileage for this year. The donor vehicle was a 1993 truck just like mine. According to the manufacturer, these are all the same truck from 1991-1994, so I wasn’t worried about the engine and trans swap.

All went well. It’s back together and running but I have 2 small problems:

Problem #1 - The red battery light is lit on the dash and will not shut off. There is a very small black wire (18ga?) hanging off the side of the alternator. I do not know where this wire should go. It DOES have positive energy coming out of it. I tested it with an inline light tester and it does light up, so I’m assuming this small wire has 12V energy coming out.

One friend suggested this wire could be my charging lead and should be connected to the battery. I do not believe this to be the case. If it was the main charging lead to the battery it would be MUCH larger gauge wire. Like 10ga or 8ga.

Another friend suggested this is the “exciter” wire that should be attached to one of the terminals on the starter solenoid. According to him, that terminal on the solenoid gets 12v power when you turn the key on. This sends a signal to the alternator and essentially turns it on. Sort of like a 12v switch. It tells the alternator to begin charging.

Problem #2 - my tachometer doesn’t work. It just sits on 0 RPM. I’m sure this is just a simple wire, but no idea where to look.

There is a single black wire that connects via a spade clip to the base of the distributor. This lead is connected. I do not know if this is the signal for the tachometer, but it might be.

Thanks for any help.


Get a Haynes manual, and look at the wiring diagrams to determine what the wires are. It’s best not to fiddle around with wires on an EFI truck blindly.

If the battery light is on, chances are the alternator is not charging the battery. This wire should have been hooked to something before you swapped engines.

Also, the wiring of the tachometer needs to be checked, also with a wiring diagram. That single black wire may be a connector to a capacitor noise filter.

I’ve got a haynes manual, a chiltons manual and also a chiltons CD disk for the computer.

Not one of them shows the wiring diagrams to the extent I need. They give very basic details and diagrams, not in-depth technical coverage.

I like good source for Factory Service Manuals and they don’t have the ridiculous processing fee that Helm does.