MSD Installation

MSD Factory Instructions
Because of temperature considerations, we usually mount the MSD unit inside the passenger compartment, either inside the glovebox area (onto the top inner panel) or onto the bottom of the  glovebox floor.  We drill a new hole and run the wires through the firewall below the starter solenoid. (Later 427s will have a hole already in correct spot.) Because of electrical interference we create two bundles of wires from the MSD unit:
  • The harness to the distributor is run down behind the engine and to the left side of the carburetor.  
  • A second bundle to connect with ERA harness #40 runs down the right side of the engine and across to the left wheel house.
Notes - Smiths tachs from Nisonger may not be compatible with the MSD.  Inquire.  Stewart Warner and Caerbont (our current Smiths provider) instruments will usually work with the hookup shown.  If you have a problem, see below.

A  voltage surge protector can be added as described here.

The MSD troubleshooting page is here.

If you a using a Unilite distributor, you must use a ballast resistor in series with its power wire.  The distributor is not built to run on the full system voltage and will fail prematurely without the ballast resistor.  Wiring a Unilite with MSD is described here.

If your tach doesn't work:
Check that all connections at the tachometer are OK, and that there is 12V at the appropriate terminal.  Check that there is 1.0-1.5V at the MSD tach output.  If not, the MSD is defective ? even if the car runs OK.

Some Stewart Warner tachometers don't read correctly over 3000 rpm.  Using the MSD tach adapter 8910 should correct this problem.

MSD wiring harness

Late Smiths tachometer:

Depending upon whether you're using an MSD ignition or not, the R/U or W/U (sometimes W) wire is used.

Always connect the black plug wire together with the black ground wire from the harness.

The black wire taped to the R/W lighting wire is not used.

The Caerbont reproduction of the Smiths tachometer is
compatible with almost all ignition systems.

Some people have had problems with certain later Stewart Warner tachometers.  
Below is a partial thread from ClubCobra about solving the problem.
Location: Southeast, CT
Cobra Make & Engine: ERA #375 427SC - 428FE - Toploader - My Daily Driver is a 1992 SC400


Yah, I think that is a good way to go. I did find that 8920 installation document on their web site. Thanks for that info.

However, I just received an email from MSD Tech Support in answer to my question (I gave them my particular configuration). They said that I should get the 8910 Tach Adaptor and not the 8920? I will confirm that. But then perhaps because you have the MSD distributor and I have the UniLite Mallory, that is the reason for the variance??

In any case, this sounds like a good winter project for me to undertake (adding to the list of things to do to the Cobra). I will get one of those on order (once I get confirmation) and we can compare notes.


Len Hurlburt
Location: Illinois
Cobra Make & Engine: Unique 427SC SB TopLoader

OK Guys - At the request of SW (which by the way is in El Paso TX now) I removed my tach and sent it to them for inspection/repair. A copy of this thread was also sent to them which really woke someone up at SW. According to them, their tach should function OK with any combination of ignition parts listed here. Right now, they don't know what may be the problem but it seems based on the information here, the tachs work OK for a time and then start to act up. In my case it was about a year. I'll get whatever information I can from SW, and share with all after my tach is sent back to me. In the meantime, you can email SW using the address a few paragraphs up. Len


Location: Harvest, AL,
Cobra Make & Engine: Unique 289FIA (351C),1966 GT350H

Just started having the same problem with my SW tach in My Unique - 351C running a Davis Unified ignition system. Worked fine up until about a week ago, then started reading about 3000rpm too high and does not go back to zero when switch is off. Pulled the tach out of the dash and checked connections, stuck it back in and it seems to read OK for now. Seems like SW should do a recall/replacement...

Unique 289 FIA - 351C powered

Len Hurlburt
Location: Illinois,
Cobra Make & Engine: Unique 427SC SB TopLoader

Phone contact at SW

Guys - Here's a phone number for Ed Mantunas, the tech specialist at SW - 925-593-1965 x138. I'm sure he would love to hear your comments on your SW tach problems. He's the guy looking at my tach right now. Len

Location: Southeast, CT
Cobra Make & Engine: ERA #375 427SC - 428FE - Toploader - My Daily Driver is a 1992 SC400

Some preliminary good news. Having the day off today, I heated up the barn and got to work on installing the MSD 8910 Tach Adaptor unit. I separated all the tach cables from the bundle of wires that run to and from the MSD. So all the tach wires (2) were rerouted away from the power wires and such. Spliced in the MSD 8910 and mounted it up in the nose, in front of the radiator cowling. It apparently likes a cool environment.

Started up the engine and the SW tach is a smooth as can be. No jitter or jumping. These are preliminary findings. Now, since I did change the wire route as well as installing the 8910, I have changed two variables. Sadly, I am not sure which of these changes did the "CURE".

Just to firm up everyones perspective... I have the Mallory Unilite electronic eye distributor with 605 unit in the distributor, the MSD6-AL box, the Mallory Power Conditioner and a ballast resistor on the red power wire 12v small.

As I get some time on this configuration, I will let you all know how this works.

With fingers crossed...

Art in CT

Location: Southeast, CT
Cobra Make & Engine: ERA #375 427SC - 428FE - Toploader - My Daily Driver is a 1992 SC400

Well guys, the Tach adaptor from MSD has indeed done the good deed for me. That combined with running the tach wires from the MSD box to the passenger's side of the engine compartment seems to have solved the problem.

The wire separation perhaps stops or eliminates something called "inductance" or in laymans terms, stops the wires from acting like a radio antenna picking up the ignition pulses.

The MSD tach adaptor went in easy and is mounted up near the MSD box. A rather simple install.

The tack is now steady and reads with accuracy. I did not change out the tach.