The other day I went to start my '74 rx3 with a '82 12a in it (so its got electronic coil ignition) and it started up, then blew the ignition fuse. I replaced the fuse, started the car again, the tachometer worked for about a second, then went down to 0 and stayed there but the car was still running. There's no specific fuse for the tach, but I'm guessing it would be on the "guages" fuse and all the guages are working. The tach flicks up just a tad whenever i turn the key to the on/off position, which i think shows it has power, and I'm obviously getting power to the coils since it's running, and tach is attached to negative post of the trailing coil, which is also indicating it has power, yet the tach stays at 0. Does anyone have any ideas?

 

The tach died and that blew the fuse. Now the circuit that failed is open and the new fuse powered up the coils again. Try a different tach. They are not very reliable.

Check to see that you are getting spark to the trailing plugs.

Lynn E. Hanover

 

Hi Lynn, I know this a old posting but I am having the some issue. My car is a 73 Rx3 I install a Msd box with 3 coils , 2 for leading,1 for trailing but I don't know what wire is for the tach. HELP!

 

The MSDs have a tach connetion. It is a resesed male spade connector on the side of the box.

It drives most Tachs just fine. This may not be the case for all tachs however.

The instructions in the box with a new MSD have most of the combinations covered. Also there is a tech phone number at Autotronics for such questions.

Lynn E. Hanover