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Rallye Dash Tach Wiring - Engine Harness


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3:49 PM
Mar 9, 2022
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I am replacing my engine wiring harness. The new one came with the gray (w/tracer) wire in the bundle. The one that connects to the coil and terminates in a single spade connector by the firewall bulkhead connector. Required for a ralley dash tach.

My car, '70 Bee (w/383 HP, single 4bbl), did not come with a tach from the factory, just the clock. My old wiring harness, factory original, does not have this grey tach wire. True, the wire harness tape is missing so the wires are bundled using a combination of wire ties and plastic flex tubing. Certainly possible that the tach wire was there from the factory but was stripped out at some point since it was not used.

The factory parts manual seems to indicate that there was only one engine harness part number, 2983808, for my application.

Striving to be true to the factory, was there was only one engine wiring harness used (which included the tach wire) regardless of whether or not a tach was ordered? That seems to me to be the logical approach which would have allowed for either a factory or dealer installed tach.

Does anyone have the factory harness, car ordered w/o a tach, with the spade connector just "hanging" by the firewall bulkhead connector?
It got a cabin side tach wire, and the firewall hole punched out, if the car was ordered with the optional tic toc tach.
Right, my buddies '70 Bee, has the same as you. His car was ordered with the factory tach.

Just not sure if it is factory correct to have that wire hanging by the firewall since my car did not come with tach (firewall is not punched). I actually had swapped out the stock clock with a tic toc tach back in the 80s after buying the car but had run a separate wire to the coil. Although it sort of pains me I pulled the tach and went back to just the clock since I decided to restore to OE.

If my original harness still had that wire then that would have been the tell. All came with the wire but since it does not I figured I would post.
Update: After scrutinizing engine compartment pictures I have of my buddie's survivor Bee, original owner, I was wrong in stating that his car came with factory tach. Someone, guessing the dealer since he does not work on his cars, added a tach. The few mods that exist on his car were made back when the car was new.

Per the pictures I see that a separate black wire was run to the coil parallel to the factory engine harness. That wire runs directly into the interior through the firewall by way of one of the interior firewall insulation retaining pin holes just below his non-punched dimple. Guessing someone removed the pin. There is no factory spade connector hanging loose by his bulkhead connector implying to me that his factory harness did not come with the tach wire run. Unfortunately I am unable to verify things in person.

At this point I am leaning towards stripping that wire out of my repo harness to mimic OE.
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