# Need Some Tach Wiring Help



## Jimdear2 (Oct 12, 2008)

This one can be real sticky. 

You first need to know what your tach was using for a signal. 

Common aftermarket steppermotor tachs use a pulsed square wave as a signal. depending on the coil type and number of cylinders. Aftermarket tachs for a older type distributor type ignition with a single coil used two ignition pulses to count a single crankshaft revolution for a 4 cylinder engine, 3 pulses for 6 cylinder and 4 pulses for 8 cylinder engines. 

When you get into distributerless ignition then the number of coils and number of cylinders matters.

What your Ford used is a mystery you must solve.

Some factory tachs used a pulsed signal, some used a voltage signal generated by the fuel/ignition system ECU. Some of the ones that use a pulse, used a signal generated by the ECU and may not match the aftermarket pattern. 

What year was your Ranger and which engine did it have. Is the dashboard a standard or optional unit. I might be able to help you track down the information you might need.

This might be a good execise to run in this thread. 

In your picture I believe the three wire unit is a hall sender. We will need to know which wire is + which is - and which is signal. We need to know what the operating voltage is, some were 12 volt and some were 5 volt (ECU internal voltage). We need to know if the sender will need an external pull up voltage applied to the signal wire.

Your friends hook up of a reed switch and one magnet indicates to me that his truck has a distributorless ignition system with waste spark coils (coils with two spark plug leads) and could be either a four cylinder or a six cylinder. If your truck is the same year and model, you will have a good start.

At least you know the wire that drives the tach.

Let me know the specifics of the engine, and the type of ignition, the year, the model, we also need to know if the dash assembly is optional. I'll try to dig out the required signal.

Jim


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## bblocher (Jul 30, 2008)

I've been through this already and it was challenging to figure out what was needed. Find the service manual for your vehicle. You should have a trouble shooting section for the tach. It will usually have you check different points on harnesses, etc and that will clue you in to the signal needed. For the last output wire to the tach it said I should see 8-12 volt pulses.

I ended up using a hall effect sensor (like the 3 wire setup you have). I built my own sensor by placing a high power magnet behind the sensor and then made a gear with only two teeth on it. When the metal from the teeth passes by the sensor it sends a quick 12v pulse out the signal wire to the tach.


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## tj4fa (May 25, 2008)

Thanks for the replies Jimdear2 and bblotcher! 

I did get some additional information from Keith Mercill another EV'er who did his '89 Ford Ranger tach mod and have attached a photo he sent showing his setup below figuring it will help me and any others looking for tach pickup signal info.

I have sent out for one of those nylon shaft collars to run on the front shaft of my motor to send the signal to my stock tachometer. I'm hoping it shows up today so I can work it this weekend.

I'm thinking the set screw will act like the gear tooth bbotcher is using. If I need another pick up, I will drill and install another magnet/setscrew 180 degrees out on the collar.

Keith Mercill hooked his up with a reed switch and one magnet had the same size engine (2.3L 4 cyl). His is an '89 Ranger and mine is a '91. We both had different computer brain systems with distributorless ignitions. 

He did say that his glass Reed switch and one magnet is running his stock tach properly. He did mention something about his ICE had two spark plugs per cylinder and that the one magnet on the motor shaft pulsed the Reed switch two times per revolution.

I think I've found a common wire that put out voltage through the old ICE computer system sensors (green with red stripe) and plan on using that as the voltage source to drive the new sensor. 

My guess is that the 3-wire Jeep sensor I'm planning to use is probably wired +, -, and signal. The center wire is white and the two outside wires are black so my first guess is that the white wire is the pulse signal wire. 

Keith Mercill mentioned the tach is grounded at the instrument cluster so he only used two wires as shown below so I many not have to use the - one of the Jeep sensor wires.

If I get to work on it soon, I'll let you know how things go! 

Keith Mercill photo of his tach pickup unit.


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