The tachometer adapter will wire in series between both banks of coils and their power supply. They are available through several aftermarket manufacturers.

Pro Comp Auto Meter Tach Wiring Diagram H1 Wiring Diagram
Autometer tach not working. Tach adapter 2650 561x 10 revc. In this case you may use an autometer tachometer adapter. Yepyou need a tach adapter. Check the tachometer wiring section in the car manual. Check your boat wiring manual to confirm your voltage if your not sure what it is. How to fix a bouncy tach needle.
Examples of these items are 5312 5313 and 5314 as well as the recently discontinued 5310. You just need to hook it directly to the box like the diagram shows. Pink power wire away from the coils connector to where it is most comfortable to work with auto meter suggests 2 6 away then cut this wire in half. If you dont find it there get the appropriate haynes manual for your car. Follow along with the autometer crew as we remedy this problem. While proper grounding of the tach and routing of the signal wire go a long way towards preventing this sometimes its not enough.
Repeat this on the other side of the engine as well. For this reason your oem tach that was circuited to read the latter does not recognize and cannot read the signal its receiving from the newer style distributor. In this case you are not dealing with a weak signal but rather a dead signal or no signal. A classic symptom of a loose wire connection is erratic display of readings. Calibrate your autometer tachometer to your engine size as follows. Check that the back of the tachometer has a switch set to 12 standard on all 12 volt tachometers matching the boats 12 pole system.
Some ignition systems are electronically noisier than others. He might but according to the chart shown on that msd webpage that i linked to the autometer tachs dont need the tach adapter. For a six cylinder engine clip just the brown wire and for an eight cylinder engine do not clip either of the wires. Sometimes corroded wire connections and breakage may be the reason for the tachometer not working. 70 chevelle ss clone 632 ci powered. Turn the tachometer over gently so that the backside is exposed.
The adapter will not use anything from the computer or the original tachometer signal wire. The fix for this situation is to purchase a tach filter or interface device. If you have a four cylinder engine clip the two looped wires on the back of the tachometer with wire cutters. What if the pull up resistor trick did not work. Run the power side pinks left right together and attach to the solid red of the adapter. Nothing besides the steps we took in the video were done.
If you are using a factory tachometer or an aftermarket tachometer that does not have shift light controls you may still use any of the above mentioned shift lights but you will now need an rpm switch an rpm activated module or playback box.