Tach Signal for Shift Light

[fish2222]

Does anyone know where I can pick up a tach signal to run a shift light with on an 85 Shelby Changer? I see that there is a ignition reference signal at one of the LM connectors, but will it work? Or is there a tach input going to the power module that I can use? There is also a tach output signal at the LM connectors, but I would think it just is a variable voltage to run the gauge, so it wouldnt run a shift light. Any help would be appreciated. Thanks.

[diabloed]

I show on my databases:

1984-87 Dodge Charger Information

Signal = Tach
Wire Color = Black
Where = Coil



Just not 100% sure what kinda signal the shift light requires

[White Lightning]

Shift lights require low voltage. The tach signal for a shift light can easily be picked up from the negative wire of the coil. In the later models, this is the factory gray wire (w/black tracer).

[xrattiracer]

yeah, the tach output signal is what you want. it is the same pulsing signal that you would otherwise pick up off the coil, but without all the timing advance and noise you would get with that.

[fish2222]

Ok then, heres a question. Will the ignition reference sensor input on the ECM work for a shift light? I would think it is just the pickup from the distributor, isnt it? Or will that only work on the 86 and 87 years?

[Una]

Yes, the LM tachometer output is a very clean signal, should work great for your shift light. I've used it to trigger the Megasquirt EFI computer on a couple cars.

[fish2222]

Is the tach output a pulsing signal though? I thought the LM converted the input from the ignition reference signal to a voltage type signal to run the tach. I didnt think the tach would run straight off a pulsing signal, but of course I could be wrong....

[xrattiracer]

yes, the tach signal is what you want, i guess i didnt explain good enough in my other post. it is a pulsing signal, one pulse per firing event. this is what tachometers and shift lights want.

[fish2222]

I am just asking if the tach output to the gauge from the Logic Module is pulsed or just a voltage signal to run the gauge. I know that I need a tach signal to use, but I am not sure if that output is pulsed or not that actually runs the tach, since it doesnt come directly from the distributor.

[Una]

Quote:

Originally Posted by xrattiracer yes, the tach signal is what you want, i guess i didnt explain good enough in my other post. IT IS A PULSING SIGNAL, one pulse per firing event. this is what tachometers and shift lights want.

What part of the previous reply did you miss? IT IS A PULSING SIGNAL. I probably sound harsh, just trying to make sure you catch the answer that was already posted.

[fish2222]

I read the post right. It just didnt specify that the tach output FROM the LM was pulsed. It just says tach signal. That could be from the coil, the distributor, etc... I was just trying to clear that up.

[Una]

The tach output from the logic module is pulsed. One pulse per ignition event.

[fish2222]

Thanks for clearing that up. Maybe I misread something, but thats all I was asking. Thanks.

[harrym]

Looks like this thread died a few years ago, but maybe someone is still out there that can help.

I have an 03 SRT-4 and I need to find an RPM (tach) signal for a shift light. I don't want to have to get a tach driver. One of the mechanics at the dealer here in Tulsa told me he found it in a manual a few years ago, but had no luck while I was there. There is a lot of talk about this on other Forums, but I haven't found a solution.

Thanks!
Harry Higear