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Discussion Starter #1
6T with Soft Touch and three step added. Output terminal on 6T has 2 volts with engine running. Can't get RPM Switches, tach or 3 step to work. This has happened since replacing the old 6T with a new one. The
set up has worked for years and now no go. Everything checks OK by its self seperately. But when the RPM Switches' white wires are combined with the tach wire (Autometer) and pluged into the 6T Tach Output Terminal, nothing works except the spark to fire the engine. Msd calls for 1.5 to 5 volts engine running at tach output terminal. Msd says the tach is bad and causing the problem. I can take the tach compeletly out of the picture and still have the problem. Is 2 volts enought to feed these three things and why no rev limiting with 3 step or with chip directly in soft touch? Have I got a faulty tach curcuit on this 6T?
 

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My first guess would be that the 6T box may be faulty. Seems weird that you replace the 6T box and now nothing works.
But the other question I have is what happen to the old 6T box?

If it were me, I would hook up each piece individually and verify that all components work by themselves. Once verified, I would add the different components one at a time.
If after hooking 2 components up and they do not work, I would point the finger at the 6T box. But try hooking different components up in different orders, i.e.: Tach and 3 step, then try 3 step and rpm switches, etc. That way you have extinguished all your options.

You could look at the signal with a Fluke 97, but this gets kinda tough to explain if you’re not familiar with using a scope

If you still have no luck I would then call MSD and get a RMA number and send the ignition back.

I hope this helps
Sparky
 

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Discussion Starter #3
MSD finally agreed that the 6T is defective. Now through the process of waiting.
Thanks for your input.
 

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Discussion Starter #4
Finally got MSD Box back. Had a bad transistor and tach output was not calibrated right. MSD fixed it and hope to be back racing this weekend. While I was having problems with this I changed the shift to work off my Pro Cube timer. Found it worked better, but I would like to rum the MSD RPM Activated Switch as a back up to the timer. Other words if something should fail on the timed shift, the MSD
RPM Switch would function as a back up to the timer for a shift. Presently the #1 timer wire triggers a 5 pin relay, pin # 85. Shifter 12v wire on 87A. How could the MSD RPM Switch be wired into this to function as a saftey back up?
 

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I’m assuming the timer throws a ground signal to the relay. If this is true, you need to cut the ground wire between the timer and relay. Put a connector on the ground side wire coming off the relay. Then get 2 mate connectors, put one on the timer wire (which ran to the relay) and the other on the Yellow wire of the RPM Switch. This way you can switch between the 2 components.

I would not recommend tying the 2 wires to the relay together. The problem you will run into here is, if the RPM switch triggers first then the timer goes off within a tenth or two of a second later, this could cause disaster.

An example of this might be: If it’s a three speed car and the RPM Switch shifts the car into second gear and then the timer goes off a tenth or two later, now your in third gear way to early.

I hope this helps
Sparky
 
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