View Full Version : Stupid Question....Tach output on #10/white wire

02-22-2006, 11:11 AM
If I connect a DVOM to the #10/white wire, what should the reading be on the meter?....

as of now I have a window switch for my NOS 5177 kit wired properly but the switch does not activate....the trouble shooting guide says the switch is not receiving an ignition signal....everything else is working normally....I can by-pass the switch and the 'noids and realys all work like they should...

the switch is an e-bay special Baker electronics adjustable switch....

I put my meter on the #10 wire and the only voltage it shows is .100 volts dc and it falls to .035 as the engine is revved....I tried using max/min on the meter to see if it was outputing the 5v @ 2 pulses per revolution....didn't I don't know if I should blame the wiring or the PCM signal or the switch itself.... :confused:

02-22-2006, 12:46 PM
I think the tach output is a pulse train, not a DC voltage,
and I have yet to obtain any good info on the format or
any 'scope photos (too lazy to pull out the gear and do it
myself, yet). Anyway high frequency content can muss up
DMMs' readings depending on the model, perhaps averaged,
perhaps not, definitely irrelevant on that signal as its basis
is not DC voltage.

I believe some switches / other tach output hang-ons can
require you to add a pullup resistor on the tach line to beat
the added load.

02-22-2006, 02:18 PM'd think the folks that made it would have done something like that as you have to tell them what kind of car the switch is going in....and they advertise it as working with an LS1....maybe they will have more insight....they haven't replied to my e-mails yet.....


02-23-2006, 12:12 PM
It is a DC digital signal the frequency of which gets varied according to the rpm of the engine. A DVM wont do any good because it is too slow to read the signal. DVMs onlyy work on analog signals and even then only VERY LOW frequencies. You would need an o-scope....If your engine is running the signal is there... ;)

Make sure the switch you are using is able to read a digital tach signal.

02-23-2006, 12:25 PM
I got an e-mail from the company and they said I should see 2.5 volts on that wire....that the signal is 5 volts and the meter averages it to 2.5.....I have nothing on my meter at all above .100 v