Test the wires in the problem circuits for continuity. I had a brand new harness where a connector wasn’t making contact with the wire. The insulation hadn’t been stripped back far enough when the harness was made up.
Power goes into the tach and then to the distributor. Because your engine runs, this wire path is good
There is another power wire to the tach that powers its operation and causes it to sense the ignition pulses. Is suspect you are not getting power to this connection on the tach
Thanks everyone for all the info. I’m still working through all suggestions. Does the fact that the ignition light stays on when the engine is running and showing charge have any bearing on the tacho problem?
Measure the battery voltage when charging. You’re looking for something like 13.8 volts. The charging light might be indicating that your voltage output from the alternator is low. When the engine is off the battery voltage should be something over 12 volts.
Voltages are good both off and running. Could it be a fault with the AW3 unit. It’s a new one but it wouldn’t be the first new electrical item to fail.
I’ll swap it with a spare to see if that’s the problem.
Sorry for late reply. Other jag problems took over precedence.
I’ve checked all the continuity and live feed to the tacho but there may be an issue with polarity of the loop around the plastic block.
Next job is to check that. If that doesn’t solve the problem I’ll check the capacitor.
I have 12v on the green wire. The engine runs so the white wire loop must be pulsing.
I need to check polarity around the loop, if that fails I’ll look at the internal capacitor.
Apologies for late reply, lots of other jag issues took precedence
I have 12.4 volts without engine, 13.8 volts with the engine running.
The green wire is live and as the engine is running the white wire must be pulsing.
Next task is to check polarity of the loop and maybe switch over the white wires in the connecting block.
Sorry for late response, many other jag issues to contend with.
Fuse 6 is good. Frank run. All wiring renewed and continuity checked. Live green to tacho is good showing 12.4v static. As the engine runs the white loop wire at the tacho must be pulsing. Next job is check the internal capacitor.
When my ignition switch fried several years ago and melted the white wire that loops thru the tach I had to re-wire that section. At first the tach would not work. I fiddled around with the loop and the block that attaches it to the back of the tach and it started working. Not really sure what the initial problem was or how I “fixed” it but all has been fine since. Perhaps it was the same type thing as smacking the TV on the side in 1968 to fix the vertical hold.