If you put an 89 Engine and tranny into a 91: ( both tranny's are 700R4 )
Your 91 cluster will need an electric speedo signal. If you used the 91 engine harness than pull the speedo sensor out of the original 91 tranny and stick it into the 89 set-up. You can't use the cable speedo unit unless you spend a lot of $ converting the dash cluster, or using a Cable X conversion. If you used the 89 harness than you will need to install the 91 speedo sending unit and splice 2 wires from the sending unit to the dash wiring harness get get the speedometer working.
** While swapping the speedo sending unit look at the speedo gear on the inside of the tranny. The one in the 89 tranny must be the same color and tooth count as the 91 tranny or the speedo will be "off".
the 89 tranny should use speedo gears for 3.42 gears
The 91 tranny ( if engine was 3.1 ) should have 3.42 speedo gears with a stick and 3.23 speedo gears with an auto.
You will not know the "exact" Speedo Sensor you need to buy until you verify what speedo gear is inside the 'new' tranny compared to the speedo gear inside the 'old' tranny !
