Tachometer Help Please

[DavidSalama]

Hello,

Just purchased Allen Holz yellow GTR. The tach does not work, so I purchase the MSD 8920 tach adapter to convert the tach signal from my MSD6
to a signal the tach should be able to read. I am connecting the white/black tach wire to the tach adapter per the instructions. I
still get no signal. The original coil + wire is not being used. Is this the problem? Can someone please explain
how to get my tach working with the MSD 6 BTM with the magnetic pickup distributer? What are the toggles on the
back of the tach suppose to be set at? Is the tach a voltage or current triggered tach?? Thanks so much!!!

Dave

[steve_d]

Do you know if the tacho is a factory unit?
Has it ever worked?
Not heard of anyone needing a tacho adaptor when using the MSD 6AL but I don't have the same dash so could well be wrong.
I assume the ignition wiring is correct or you would be repoting dead engine.
Can you work out how everything is wired including the wire colours?

Steve

[yiihaa]

With the standard American Speed setup you will have an MSD 6AL. The magnetic trigger from the dissy is green/violet and is connected to the MSD6AL.

The MSD6 range has a tacho output that produces a 12V square wave with a 20% duty cycle (according to my instructions!). This output is via a spade connector on the side MSD box, below or above the magnetic pickup connectors (green/violet).

This needs to connect to the white with black stripe cable on the factory loom (which is labeled in the build manual as connecting to the coil). This part of the factory loom comes out somewhere near the back of the engine as in some installations these two wires connect straight to the coil, so you'll have to splice in an extra length of cable from the MSD box to the white/black wire. The paired white cable in the factory loom connects to the lightweight red cable to the MSD box (this is a switched 12V).

The msd box then has an orange and a black wire connecting to the coil, these are the only two wires that should connect to the coil (except for the HT lead).

This setup works fine with the factory VDO gauges and no MSD tach adaptor is required.

[stig]

As a matter of interest, with the standard AS dizzy/6AL/coil setup - what model is the distributor?

[yiihaa]

DavidSalama said:

Hello,
What are the toggles on the
back of the tach suppose to be set at?
Is the tach a voltage or current triggered tach??

voltage triggered tach.

Toggles on the back of the tach set how many cylinders,

For eight cyclinders:
Dip#1: On
Dip#2: On
Dip#3: Off

See here for instructions:
www.egauges.com/pdf/vdo/0-515-012-020.pdf

[DavidSalama]

My tach is the factory tach with the 6 toggles on the back. Does anyone know the correct toggling of this type tach? I already have a switched power source to the MSD box, so the large white wire next to the white/black wire is not used. Is that fine? Perhaps a fuse is blown somewhere? Supposedly, there is a 3 amp fuse in line somewhere? I will have to check the fuse box and wiring schematics, unless someone wants to tell me if you already know. I assume there are no inline fuses to look for. Is there any way of testing the tach to be sure it works? I've already tested the MSD Tach output and can get a tach reading on my voltmeter. Any other suggestions welcomed.

Thanks.

[steve_d]

Do you get the same voltmeter reading at the Tacho? Broken wire?

Steve

[DavidSalama]

I will test the white/black impulse at my tach loom later. With persistence, I will get to the bottom of this. Don't know how to test the actual tach though.

Dave

[yiihaa]

Have you tested continuity of the wire connected to the tach output and the black/white wire connected to the tacho? Sorry if that is a bit obvious.

(PS the dissy on my 540BHP AS engine is an MSD V8 pro-billet, 85551)