crazy tachometer problem

[cruznude]

Okay so I hook up the tach and as soon as I turn the truck on the needle jumps to 5 and doesn't move until I turn the key off.  Any ideas about whats happening here? Oh by the way its on my 620 and the tach is an original from a 620.

[datzenmike]

 

 

Okay so I hook up the tach and as soon as I turn the truck on the needle jumps to 5 and doesn't move until I turn the key off.  Any ideas about whats happening here? Oh by the way its on my 620 and the tach is an original from a 620.

 

 

 

Turn the key to ON or start the motor?

 

5 RPM?  hundred? thousand?

[DAT510]

What kind of tach is it? Stock 3 wire or 4 wire? 

IE: Induction type or voltage signal 

[datzenmike]

Ahhh, you see I read it was a '79 620 tach. Yes it could be an induction type and won't just wire up to a '79. If it is it CAN be wired up without too much trouble.

 

Inductive type tach... note #4 and#5 wire loops through

 

 

Voltage signal. (your '79 should have this one)

[ggzilla]

Yep, early 620 tachometer can be used in later 620 by finding the IGN wire in the dash harness, cutting it, and putting spade connectors on it. Then plug the wire ends into the harness (wires #4 and #5).

[datzenmike]

I think you have to wire the inductive tach between the dizzy and coil so it senses the current flow.

[ggzilla]

In the Datsun factory wiring harness, it is wired in the dash, in the coil supply line (IGN wire).

 

Between coil and distributor is a make/break connection. It may work there too.

[datzenmike]

It's how I had to wire my inductive up in the 620. The '79 has a single Blue wire from the coil negative terminal. The dash end goes nowhere. It's meant for the other style tach.

[ggzilla]

Yes, I've heard that will work. It is not the way Datsun wired inductive tachometers but if it works, then it works.

 

The 1979 has a wire under the dash that supplies power to the ignition coil (in addition to the 1979 tachometer wire). Inductive tach does need a wire to "go to" the tach, instead the tachometer senses the current changes flowing though the wire.

[cruznude]

Thanks DM,Dat 510,GGZilla, for the quick replies. Sorry I've been away for the weekend. Okay I turn it on and started and the tach jumps up to 5000 and stays there.  I  rev the motor and it stays there.  It doesn't move at all except for when I shut it down and back to nothing.  Of sorry I have the voltage type tach.  So my other question is there too much voltage going there and do you think I'm going to try to hook this up an alternate way?

[datzenmike]

Is there a plug on the tach? does it match your '79 harness?

[cruznude]

Yes and thats what I'm plugged into. So,what do you think is going on? maybe it needs to hook up to something else also?  I just don't know..

[datzenmike]

 

 

So you sure it's this one? The Black/Green wire should go to a Blue wire in the harness plug.

[cruznude]

Okay, its late and let me go out there in the morning and take a look at this all again and see where I stand. Thanks DM

[73DATSON]

Does anybody have a diagram for the factory tech? I just got a white needle one with four wires? And I was told its for 70-73 510? It does fit perfect:-)

[ggzilla]

I don't think a 510 tach will be a good one to use in a 620. Maybe create a new topic for your question?

[datzenmike]

It's for a 620???? :lol: :lol: :lol:

 

Well it should still work but forget looking for the factory wiring plug. Also you may have trouble seeing it at night. :lol: :lol:

[73DATSON]

No it's a 73 510

[datzenmike]

Ah you're in someone else's post.

[73DATSON]

Yes:-) I notice this was for a 620, so I did a new one.