EFI and MSD Tach wire

[troublemaker]

Hey folks, thought I would pass this on. I am running a FAST efi with a FITECH 6 barrel throttle body, MSD 6al, MSD distributor and coil. The MSD tach wire is connected to the efi module. The dash tictoc tach. needs a signal. The tach. has been reworked for an MSD signal. My question was where to get the signal? Various articles are posted throughout the internet, piggyback off the MSD feed or come off the negative side of coil, MSD Instructions tell you to never connect to the negative side. I called MSD, they told me what I figured, stay clear of the negative side, splice the tach wire as close as you can to the box, the MSD box will adequately feed the efi system and the tac.. Plan on doing it this weekend and will let you know how it works. Just an FYI for anyone messing around with EFI. This is on a 70 RR 440, 4 speed.

 

[pnora]

I thought the MSD box had a tach signal ? Usually the gray wire. What box do you have?

 

[troublemaker]

I have an MSD 6al, the Grey wire generally used for the tac signal coming off the box is now going directly to the FAST EFI module. 1/2 the posts I read say that splicing into the grey wire will cause spikes to the module and create a dirty signal-MSD informed me that wasn’t true. Just thought I would share.

 

[71RRHI]

I have The MSD 6 Digital Plus, and FiTech. I have both the FiTech and a Autometer tach spliced into the tach output of the MSD for over two years. No problems so far.

 

[troublemaker]

Thank you, that’s what I wanted to hear.

 

[pnora]

I have an MSD 6al, the Grey wire generally used for the tac signal coming off the box is now going directly to the FAST EFI module. 1/2 the posts I read say that splicing into the grey wire will cause spikes to the module and create a dirty signal-MSD informed me that wasn’t true. Just thought I would share.

At this point I would try it and see how it reacts. If everything works so be it. If there is an issue you could try a diode on the tachometer feed.

 

[troublemaker]

I’m going to run the wires like 71RRHI did, and like MSD suggested. Thanks guys.

 

[Don67Satellite]

I’m running FiTech EFI on my 440 and I have a MSD 6A with the tach signal output. Both the EFI and my Sun Supertach II piggy off that with zero issues.

 

[Paul_G]

I am using a factory tach in my 73. Had to use the MSD tach adapter box. I tied the EFI and the tach adapter box both off the tach output wire of the 6AL box. No issues.