taz68camaro

Hoping to correct this problem and this is the place to do it. I have a transplanted 08 Trailblazer SS 6.0/ 4l70 combo in a 68 Camaro. I installed the Autometer 5" electrical tach but it's not working...the lights work in the tach, but the needle doesn't move. Shouldn't I see less than 3 volts at idle and as rpms increase the voltage increases also instead of a constant 13 volts that I'm reading on the multimeter? Do I need the LS tach adapter harness from Auto meter? I just don't want to throw another $200 at it if I'm not getting the correct voltage at the signal to start with. Any help would be greatly appreciated. thanks

JoeNova

The LS outputs a 12v square wave frequency for a tach signal. There is no varying voltage.

taz68camaro

Autometer tells me there should be some movement of the needle if there is an output on the engine speed signal wire. Is the steady 13v an indicator of correct signal then? If it is then it should be a matter of setting dip switches?

2xLS1

iTrader: (25)

A DVM is not going to be able to read frequency on a DCV scale. You need to look at the output with a scope or frequency counter.

taz68camaro

I have neither scope or counter, but, if there is 13v at the signal wire could I assume that there is in fact a square wave that the meter is not fast enough to read? The tach signal of the 08 Trailblazer SS is supposed to be a 2 pulse signal but when I set the dip switches to 2 pulse, (4 cyl), it still doesn't work. Autometer tells me I need the LS tach adapter...another $185. Just don't want to keep throwing money at this but if I knew it would make it work, I'd do it.

jcvett56

Are you using the factory E67 TBSS computer? Who has tuned it? There are settings you can alter for tach output that could render the output wire inoperable. If you have HP Tuners post the tune.

You need to have a pull up resistor, 4.7k, on your tach output wire for an aftermarket gauge to read the signal. On all our harnesses here we test our speed output and tach output with an autometer gauge.

taz68camaro

Yes, I am using the factory E67 computer. Since my last post I bought the Autometer tach adapter, 9117, which is half the price, just have to cut and splice as opposed to plug n play. I haven't had a chance to splice it in yet. I've heard 1k resistors, 4.7k....but I will try the 4.7k first. Thanks for your input, greatly appreciated!