[DeTomaso] 8920 Tach Adapter Checout In The Car
Thomas Tornblom
Thomas.Tornblom at hax.se
Sat Apr 17 02:51:33 EDT 2010
SOBill at aol.com skrev:
> EA,
>
>
> Installation
> The White wire of the 8920 must be connected to the Tach Signal connection
> on the 6A. The Tach Signal connection on the 6A will have a 20% duty cycle
> 12v square wave on it. One pulse for each spark occurrence.
This sounds like the tacho could be made to work by just bypassing the
series resistor on the tacho signal.
Didn't you have a schematic for the tacho?
Cheers,
Thomas
> The Black wire of the 8920 must go to a good chassis ground.
> The Violet wire of the 8920 must be connected to the Blue/Black wire which
> goes to the Pantera Tachometer input terminal. There must be no other wire
> connected to the Blue/Black wire. My car was built with the Blue/Black
> (Pantera Tach wire) crimped into a common terminal with the Blue wire which
> goes to the breaker points and condenser in the OEM distributor. To be safe,
> be sure the Violet wire is connected ONLY to the blue/Black wire.
> The Red wire of the 8920 should go to the same place as the small Red wire
> of the 6A. This should be 12V when the ignition is in Start or Run. Fuse
> #12 is a good place. Using the Pink ballast resistance wire which previously
> went to the plus side of the OEM coil may work, but I would wire it to
> Fuse #12. You can do this easily thru the passenger side rocker area using the
> seat belt attachment opening.
> The 8920 takes the 12V Tach signal of the 6A and converts it to a signal
> equivalent to what would be found on the Negative (breaker point) terminal
> of a points/coil ignition.
> Checkout
> You can verify that the 8920 is working in the car using a multimeter. In
> the following, +12V DC means the voltage of the battery.
> With the engine running the White wire between the 6AL and the 8920 should
> read around +2.8 V DC. This indicates that the 6AL is providing a 20% duty
> cycle +12 volt square wave to the 8920. This voltage will not change with
> the speed of the engine because the signal duty cycle % does not change. If
> the White wire reads 0 V DC, you may have a bad connection. If the White
> wire reads +12V DC, the 6AL tach output signal is bad.
> With the engine running, the Violet wire tach signal out of the 8920
> should read as follow:
> 1,000 RPM = 1.27 VAC, 2,000 RPM = 2.62 VAC, 4,000 RPM = 4.75 VAC
> This indicates that the 8920 is putting out the normal point/coil type
> signal to trigger the Pantera Tach. Note that we are reading AC voltage here
> because we want to see the inductive ringing signal which occurs with each
> spark occurrence. The AC voltage reading on the Violet wire increases with
> engine speed.
> With the engine not running, if you disconnect the White wire from the
> 8920 (i.e. remove the 6AL tach trigger signal), the Violet wire of the 8920
> will read +12V DC. With the White trigger wire then reconnected to the 8920,
> the Violet wire will read slightly less than +12V DC. Although the
> difference between readings is only on the order of 0.5V DC, this is a second
> indication that the 8920 is working correctly.
>
> Have fun,
>
> SOBill Taylor
> sobill at aol.com
>
>
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--
Real life: Thomas Törnblom Email: Thomas.Tornblom at Hax.SE
Snail mail: Banvallsvägen 14 Phone: +46 18 444 33 21
S - 754 40 Uppsala, Sweden Cellular: +46 70 261 1372
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