Installing a Scirocco Tach in a Rabbit

Rabbit clock - to - Scirocco tachometer COMPLETE: (added for search)

The tach I was using was a 12-pin unit from a '76 Sciroccco. The Rabbit (1975) is 12-pin also.

I swapped the clock, added the tach and pressed circuit board, drilled a small hole for the voltage regulator and thought I was done.

"VW's wiring connections on the 12-pin harnesses would 'likely' be the same", I thought. WRONG.

I should've traced the wiring to make sure: I plugged in the hybrid cluster, hooked up the battery, and heard two "zaps". The tach didn't work, and that was the least of my problems. The instrument cluster lights were dead. The turn signal lights didn't function. The high beam indicator light was always on. Fuel/ temp gauges quit working. And I had glowing warning lights all over the place. Not good.

I pulled the cluster and now had two blown connections on the circuit board.

I tried "SEARCH": searches say only one pin ("#4") is different" between the harnesses. It's 12V positive clock power for the Rabbit, and a terminal 1 coil signal for the Scirocco.

Not the case with me. There may be "early" and "late" harness configurations on the MKI Scirocco?

Here is the ORIGINAL wiring setup on my Rabbit, and what I had to change to match the (now-repaired) '76 Scirocco 12-pin board:

Pin 1.....Blue (red stripe): Turn signal light
Pin 2.....Blue: Alt warning light
Pin 3.....Blue (white stripe): High beam warn light
Pin 4.....Red: Clock (+) wire or tach (term 1) signal
Pin 5.....Brown: Ground
Pin 6.....Gray (blue stripe): Inst. cluster light
Pin 7.....Black: Positive 12V constant
Pin 8.....Purple (black stripe): Fuel gauge feed (from sender)
Pin 9.....Blue (yellow stripe): Temp gauge feed (from sender)Pin 10...Blue (brown stripe): Cat converter indicator (if appl.)
Pin 11...Blue (black stripe): Oil pressure warning light
Pin 12...Blue (green stripe): EGR control (if appl.)

And here's the changes I had to make to the harness:

Pin 1: NO CHANGE
Pin 2: moved to position 9
Pin 3: moved to position 2
Pin 4: moved to position 3, disconnected midway in cluster harness, and routed to coil terminal #1
Pin 5: moved to position 4
Pin 6: moved to position 5
Pin 7: moved to position 6
Pin 8: moved to position 7
Pin 9: moved to position 8
Pin 10: moved to position 11
Pin 11: moved to position 10
Pin 12: NO CHANGE

Write-up courtesy of clintg60-16v of vwvortex.com

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