[WW3]

No, not the brand MSD but rather Summit's Multiple Spark Discharge w/rev limiter. Any way, installed it and got it running but the tach won't work. It "blips" up 200 RPMs when the key is turned off, but is dead other than that.

Summit's tech line was of little if any help as their Pontiac tech said to " jump the tach filter and it'll be fine". Well I see no tach filter on the brown trigger line other than the inline fuse holder and I recall nothing other than a 12V feed to the fuse box and this trigger line that hook onto the back of the tach.

Now, I understand that this digital box uses a square wave, 20% duty cycle signal to the tach. And I*thought* the factory tach used a pulsed 12V signal.

So, has anyone had this problem? and how did you get the tach to work.Am I missing this tach filter somewhere?

[Brian Baker]

My 79 T/A tach worked fine using a MDS-6AL, connecting the brown tach wire directly to the tach lead on the MSD box. Summit's box is very likely manufactured by MSD and repackaged for Summit. I know of no "filter" in the tach line, unless it's an RF filter. Do you have the box connected correctly to the HEI?

[WW3]

Yes, it's all hooked up correctly,not a whole lot to screw up there. But I'm guessing Summit's brand of ignition box is made by Mallory and not MSD. IT looks like the Mallory case and is digital and not analog like the MSD brands.

[billygoatii]

Have you tried calling Summit's tech support?

[TropicDave]

Originally Posted by WW3

Summit's tech line was of little if any help as their Pontiac tech said to " jump the tach filter and it'll be fine".

Yes, it appears he did.

[WW3]

Yes, at first he said I needed an MSD tach adaptor then he consulted someone else who told him that I needed to just bypass the tach filter.