tach not working

RickKlem · 09-14-2003, 01:50 PM

I was having problem with setting up my MSD 6al so I pulled it out and installed the permatune cdi and a factory coil. The problem is that the tech is not working. I used the black /purple wire goes to the tach and connected it to the Black wire (TD) from the 6 pin connector and now the tach doesn't work.

How can I test it? Did I connect to the right wire coming from the cdi unit?

Rick

RoninLB · 09-14-2003, 04:23 PM

I'm not sure what the TD connector is?.. but the '77 has a 3 pin Permatune and later models have a 6 pin.. so I'm posting a 3 pin for your '77.. the connection for thr 2 into 1 tach wires is under the engine fuse/elec panel inside the taped bundle..

RickKlem · 09-14-2003, 06:24 PM

Thanks Ronin

But I guess that I should have mentioned that the motor has been changed to a 80 3.0L with a 6 pin cdi box. The 6 wire connector has a black wire (TD in the pinout discription) that (I think) should signal the tach. I just need someone to confirm this.

Rick

RoninLB · 09-14-2003, 11:29 PM

Quote:

Originally posted by RickKlem
I should have mentioned

I'm no prize either!

but how about some color to help this out.

CamB · CamB's Garage

What did you do with the tach and the MSD before putting the permatune in? Specifically, did the tach ever work wtih the MSD?

RickKlem · 09-15-2003, 02:38 PM

Yes , the tach worked when the MSD 6al was installed . It work correctly , no spikes or jumping . I was troubleshooting a different problem so I connected the permatune and factory coil for testing reasons. I connected the same black/purple wire coming from the tach that plugged into the bottom of the MSD and spliced it to the (td) black wire coming from the the permatune connector. Started the motor ,no tach movement what so ever.

Is there a fuse somewhere ? Is it possibile to test the signal out of the permatune to make sure It is sending a signal or voltage?

Thanks
Rick

CamB · CamB's Garage

That's wierd.

The MSD gives a +12v signal (pulses) - presumably the permatune does the same. You should be able to test it with a multimeter?

Early_S_Man · 09-15-2003, 03:15 PM

Rick,

The '77 tach was designed to use ground pulses from the distributor points.

The 6-pin 'TD' signal from the CDI-unit is a shaped version of the trigger signal from the magnetic-pickup in the distributor. Not all early tachs will properly trigger from the SC-style CDI-units or Permatunes.

CamB · CamB's Garage

Warren

I think that the MSD does the same (shaped signal) - from memory it refers to a "12 volt square wave".

Which is why I reckon it is weird the tach works with one and not the other. Could the 6-pin TD signal be lower voltage??

mb911 · mb911's Garage

I did the same conversion with the same year conversion parts with an MSD box and my tach worked as well no problems

Ben