Re: Anyone install an MSD on their Howell TBI??
Here is some info from customefis.com that I saved before it was taken down. This is where I got the idea to do what you are doing - using a second ignition module to provide the reference pulse. In my case, I have a 4-pin HEI module in the dist and am using a 7-pin HEI module in parallel to send the ref pulse. I am hoping that once the fuel side is tuned, I'll be able to install the 7-pin module into the dist (again using instructions from the old customefis.com site) and control timing using a custom chip. I am in the last stages of putting my system together so I can't say whether it works for me or not. Anyway, here is the info, I hope it helps:
"The second method is to use two ignition modules and wire the magnetic pickup in parallel into both modules. The computer controlled module then only connects to the ECM to provide a reference pulse and nothing else. The stock ignition module is left intact and continues to fire the coil normally. This method could be a viable way to keep the stock timing curves so that you can work on the fuel only control before attempting to work on the spark timing. I use this method often when trying to diagnose if the ECM is controlling timing correctly."
"Connect the magnetic pickup wires to the P and N terminals on the GM ignition module. For the Ford Duraspark, the purple wire goes on the P terminal and the orange wire goes on the N terminal. The polarity is important and the only way I know to tell which way to hook one up is to try and check the timing with the GM module firing the coil. "