Let me start by saying that the end goal of this post is to ensure I have a functioning electronic tach signal compatible with the Zip electronic tach conversion kit before tearing out the dash.

Recently purchased a 69 coupe which runs great and I'm really enjoying it. The previous owner replaced the original 350 SBC with a crate engine (probably in the early 90s) that included GMPP/ACDelco Heavy Duty electronic ignition and he didn't replace the manual tach. The ignition control module is P/N 10037378 (pictured below) and distributor P/N 10134355. What few details I've found insist on not using either one with production HEI systems which implies to me that the signaling is a bit unique. The control module has a tach signal output but when connected to a cheap digital tach it's reading probably 3x true RPM at idle. I'd really like to find technical specs for these two components but they're old enough that I'm not having any luck finding anything online. I'd settle for some advice on a filter solution that will eliminate what I assume is the multi-spark pulses or someone with experience to assure me that the Zip conversion kit will work w/o a filter. Any feedback would be appreciated.

 

That looks the analog MSD 6 eh? I'll tell you what I did and you can go from there.
I installed a tach from a 1976; initially with a tach filter...but I had to disconnect the tach filter because it would make the tach bounce when I hit ~3500 rpm. Pretty sure I took the tach signal off the MSD-6 box.
Let me know if you want to verify where I got the tach signal. BUT anyway, it works like a dream and has for years....

 

I'd you have another thread that we were discussing this on....its better to have one thread so we can follow along and refer back to info.....what distributor are you using now. What are you going to use? If it was a converted dizzy that had an induction pickup and used a seperate box like that and you are switching to the all in one hei you don't need any off that or the filter, just a clean power force usually pulled from the yellow wire feeding the wiper motor. If you are looking to find a new dizzy msd makes one that will use the mechanical tach drive. Otherwise the msd box provides a signal which needs to be calibrated or the stand alone GM dizzy has a tach output that needs to be calibrated...its not the source it's the tach itself.
Use a timing light with tach function and make a box and put your tach in it to protect it and you can calibrate it on your fender before you install it, but you have to run your car at 1500 rpm and again at 4000 to do it by the directions.....or just buy the $50 dollar tool then resell it .
Or buy this and figure out how to make it work for your signal..https://www.amazon.com/Generator-DROK-Adjustable-Frequency-Rectangular/dp/B07KVYQ78K/ref=pd_aw_ci_mcx_mh_mcx_views_0?pd_rd_w= ok4df&content-id=amzn1.sym.eeeda21f-f942-4067-b2fd-e3ffbfbe7c3b%3Aamzn1.symc.2b06b7e8-a86c-4e6e-b02c-90d58278f4f1&pf_rd_p=eeeda21f-f942-4067-b2fd-e3ffbfbe7c3b&pf_rd_r=7BHQCQDZY5YB6JWKY1A A&pd_rd_wg=CbNdY&pd_rd_r=226e8847-207b-4dff-99bf-76962d8a8242&pd_rd_i=B07KVYQ78K

 

I am using the Zip tach part on my 69 with a Daytone Sensors capacitive discharge box. It works fine without any type of filter, but be aware you need to calibrate the tach unit before final install. I have done two of them and needed to calibrate both to read accurately.

 

Thanks for the advice carriljc, I'll start watching ebay for this option.

I had seen some references to this GM control box being rebranded MSD, that gives me a better chance at finding documentation. The distributor (GM P/N 10134355) doesn't have an obvious tach output but the control module harness has a white tach lead that is unused in this car so that's what I'm using. I really don't trust the cheap Chinese digital tach I'm using to prove I've got a reliable signal, I may wire up the Zip conversion kit that I already bought to see if the 3x reading is consistent.

 

Thanks for the reply Scott. I'm not planning to replace either the ignition control module or distributor, the car runs great and the previous owner did a good job with the crate engine install, I'm just trying to get back a working tach. I'll need to look into the calibration for the Zip conversion kit, thanks for the advice.

 

I suspect that the conversion kit will work with that Pseudo-MSD thing.
You can write to ZIP and just ask them if it will function properly with an MSD box.
....and some info FYI;
https://67-72chevytrucks.com/vboard/...54&postcount=4

Per the above link it is the same as an MSD-6T....and if so, then is compatible with GM tachs..per this document: https://static.speedwaymotors.com/pdf/547-6400.pdf