[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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