how to hook up speedo???
09-01-2004, 08:56 AM
#1
8 second mod
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how to hook up speedo??? I just did the th-400 swap, im guessing i need a autometer mech gauge. anyone do a speedo with the 400? any help would be great 
09-01-2004, 09:43 AM
#2
From the TH400 FAQ above, this is the post I made:
My speedo is pretty close, not because it doesn't work, rather the gear ratio in the ECM is maxed out and I can't use my current settings. The limit for a 98 ECM is 25.6" tires with 4.10s, It does work with 28" tall tires and my 4.33 gears though. 
For your's, you'll need to multiply the speedo signal from the TH400 2.5x to read properly. This can be done with minor changes in your ECM.
Originally Posted by 12secSS
Use the speedometer items from a 4L80 (3 speed trans) truck, part numbers were previously posted (GM# 8655291, 8655315), they work perfectly on ex-A4 cars. Just cut the wires from the 2-prong connector under the car and splice them to the new connector (p/n: 12085498)
For your's, you'll need to multiply the speedo signal from the TH400 2.5x to read properly. This can be done with minor changes in your ECM. 
you just need to modify the input signal to your ECM as I stated.