359 tach signal wire

On a Delco type altenator the terminal could be a "T", "S"' or "W", for Tach, Sense, or Waveform respectively.

 

That's a Leece Neville Alternator, I am guessing it is a 8LHA 140 or 160 amp alternator.

SO it is really simple, the three terminals on the bottom are Stator taps and can be used for a tach. It is 8 pulses per revolution of the alternator.

 

The tach signal comes from bottom of the rear structure. A speed sensor reads the flywheel ring. The harness is a twisted pair all the way up to where they hook to the rear of the tach

 

The thing is though the wiring should already be there.

I'm not sure which trucks had it and which did not, but most of those trucks had a magnetic sensor under the bell housing that reads the flywheel rotations.

If you're saying that your tach was working and then somebody changed the alternator you need to go back to them.

Sounds like there's a story with that and you probably don't want to go back there, and if not you need to get some long test wires and an ohm meter and find where those wires are for your tach.

For the hell of it I would just crawl underneath there and see if you do have a sensor under the bellhousing.

And if it only had a connection at the alternator, you've got to keep looking down the frame. The wire has to be there.

And in the worst case scenario, you're going to have to run your own wire from the tach to however you're going to read it whether it's the alternator or the sensor on the bottom.

I don't know what kind of truck you have but I think on most of the trucks the wiring harness comes out on the right side and there's a plug there and inside of that harness the tach wire is somewhere in there. You have to look through a wiring diagram to see which wire it is but you could jump it there if you had to.

I know it's a pain in the you know what and maybe you'll have to hire somebody to do it, but of all the problems you have it's really not that big and it shouldn't cost you much, even if you have to pay someone to fix that up for you, unfortunately.

 

Anything loose in the battery box?