tach not working

[bob deluke]

In the process of sorting out electricals for my 77 Targa as it had a dash fire when I bought it. Can't get tach to work. It has a permatune(doom) CD box. Checked dist. point, adjusted correctly, voltage at tach terminals are: 13.5vdc between ground and red/black terminal, 6.5 vdc between ground and black/purple wire at tach. Engine starts and runs fine, have 13.5 vdc at battery. If you tap on tach face, needle moves o.k. so its not stuck. Looked through previous threads regarding tach and thought it might be diode d-8 as suggested by Wayne. Took cover off permatune and it's completely potted! No access to circuit board. model #c.a.r.b.EOD-210. s/n 61574-911. Any suggestions?

[Early_S_Man]

Bob,

If you have steady 6.5 Volts DC at the Black/Violet wire at the tach with the engine running, then you aren't getting any signal from the points! Check the Black/Violet wire in the 2-pin Nylon connector at/under the electrical panel for corrosion or looseness.

You have to be getting the 12 Volt pulses from the points to expect the tach to work! You can use a 12 Volt test lamp to check for pulses from the points.

There is no D8 in a Bosch 3-pin CDI unit ... that was in a 6-pin unit for SCs and Turbos. Permatune, who knows???

[bob deluke]

Warren, what do you mean by "connector at or under electrical panel"? Am I looking under the dash for this nylon connector or in the engine compartment? By the diagram, I guess I should be looking under dash someplace. Thanks for your help, will let you know if I find the problem.

[Early_S_Man]

Bob,

The electrical panel on the left side of the engine compartment is where I was referring to ... the 2-pin connector will be relatively close to the CDI unit, just a few inches.

The 2-pin connector may be under the panel, or it might be just sticking out of the taped bundle of harness wiring going forward. Look for the Black/Violet wire that goes to the CDI unit.

[bob deluke]

Thanks Warren, I know where you're talking about, will check that out tonite and let you know. Thanks again for your response..