Engine swap and now Tach doesnt work?!

[pyite20v]

I have been reading threads for hours but cannot seem to find my exact issue.

I have a 72 that had an 83 SC 3.0 in it. I did an engine swap last weekend for a ROW 3.0 from 1980. Everything works great except for the tach, which doesnt work at all. Turn signal lights and high beams seem to work, and it worked fine before, so I am not sure which step I am missing.

I tried two CD boxes and both seem to work fine. I was told the new engine has an alternator with an external voltage regulator, but everything else is the same. I have checked for loose wires on the back of the tach but all seems to be fine.

Any ideas?

Anyone in the mill valley or SF area have a spare tach I can put in to make sure the tach hasnt gone bad? (although it worked fine last week).

[timmy2]

Check tach pin out on the new versus old 14 pin connector. I believe it is pin 12 on the connector for the '80, may be different on the '83 to match the '72 chassis.

[pyite20v]

Okay timmy2, what am I looking for?

[timmy2]

Check the continuity from 6 pin CDI harness connector (middle black wire) on the new wiring harness goes to the same pin as the old one did on the 14 pin connector.
I'm out for Father's Day with my boy right now. I'll check back later.

[pyite20v]

Okay I took the covers off of each connector and I defintely see some differences.

Here is the old connector


Here is the new connector


Here is the pin box



The wires are definitely in different spots for the old vs new harness. How can I tell what goes where?

Thanks!
Happy Fathers day!

[pyite20v]

Yes thanks for the lead timmy! I rearranged the wires so they mimicked the old wires and now my tach is back!

This is great because now I can really wind the new engine out and actually know where redline is!

[timmy2]

There ya go!
It's drive it like ya stole it time