Hello,

I have tried getting responses for my questions in LT1 tech and all I get is views, but not 1 response.

I have a 95 TA. I have a Mallory 685 CD Ignition. I want to hook up a shift light to the tach output on my Mallory box.

I do not want to use a proform shift light because that is what I have right nowand it is off by at least 700rpms when I hook it up to the tach output on my mallory box. Before I had it hooked up to the pcm it would read still read incorrectly. I used the rpm gauge on the dyno as a reference, not my car's tach.

I would like to use this shift light http://store.summitracing.com/defaul...ight&x=13&y=13

I know I have to use a an MSD "pill" I was going to plug in a 6600 or 6800.

Will this shift light work if I hook it up to my Mallory tach output? I do not want to hook it up to my pcm or coil.

If this shift light will not work, which shift light will?

Thank you in advance for any responses.
Lalo

 

It's always recommended to hook a shift light or tach into the tach output of the ignition box. All the output does is send a pulse signal which the tach or shift light pick up. You will need a special shift light as you mentioned above in order for it to come on at a preset limit. You could also use a plain shift light connected to an rpm activated switch.

My ignition has 2 built in rpm switches. I use a normal shift light that came with a cheap tach (tach failed already) and installed a multi LED bulb in the shift light. I use an Autometer playback tach now but only look at it when I'm running the engine up in the pits and to watch the results after a run. Once I'm on the starting line I only conventrate on the shift light.

What are you comparing the Proform light to when you say it's 700 rpm off? Don't compare it to the factory tach. That's far from accurate over the entire rpm range. The tach output off the ignition is a better tach source.

 

The dyno. When I hit 6900 on the dyno's rpm display, my shift light came on at 6100, 6200

 

Mine only has one and I am already using it for the nitrous.

So what shift light would work correctly with the output wire on my mallory box? Specifically, will the previously mentioned MSD shift light work?

 

I wanted to hook up a shift light to my 685 box also. Didn't realize it only has a rpm window switch. So for now I used a light I bought from Radio Shack ($2.95) and connected it to the window switch. The light comes on when the nitrous is activated and goes off when the nitrous is shut down. I just shift when the light goes out. It's not that bright so it don't bother me being on that long. Oh well, it was cheap.

 

It does have a wire for tach out. The problem I am having is that my proform shift light is not coming on at the right time when I have my shift light hooked up to it. I was hoping that an MSD shift light would be more accurate, but I am not sure if the MSD will work correctly with my mallory box. Seems pointless for mallory to sell a box with a wire for tach out and it not work with a single shift light.