I just Installed a MSD 6a WHAT A difference 100%
Now my tach will not work. I have searched the forum for what I need to do. I have found no real answer some use the MSD adapter 8910 others the 8920.
I have a 73 fuel injected 2.0 with pertronix. According to MSD the 914 (mine) the tach wire used to go to the Negative of the bosch coil and it is called a Voltage Trigger and says to use the 8910. I have read others using the 8920 with no problem. below are two diagrams I found. Which is the correct one to use



8920



8910

THANKS

I found this on line about the 8920
http://www.msdignition.com/forum/archive/i...php?t-8649.html

I made the 8920 diagram and that post on MSD's forum is mine. I used the 8920 because it came with my box when I bought them used. It works fine. Well it did at least until the 6AL box failed! I *think* you can use either adapter. But I know the 8920 works.

If you can't get it to work with either MSD adapter PM me.

Thanks for the information

I just came across this on the forum that explains how to do a little modification on the Tach internals by using a jumping cable. Has any one tried this or is it safer just to spend the extra about $70 for the MSD adapter 8920

http://www.914world.com/bbs2/index.php?act...hyfire,and,tach

Here's my posting when I finally got it to work...

-- Rob

I dont think you need an adapter....

The dizzy tells the BOX when to fire the coil right?
Hmm... the only wire coming out of the dizzy to the box is a signal wire.....

you should be able to tee into that wire and have a tach pulse (it used to be the wire going to the negative side of the coil before the box was installed)

works with my mallory box and dizzy this way

Yes.. the white wire in both mallory and MSD 6a boxes is a trigger wire. 1 pulse per plug (the box decides when to do multispark discharge... not the dizzy)


Tee into the white wire out of the MSD 6a box

Thanks Aaron I am going to try what you said. If it does not work for me Then I am going to buy the 8920 adapter.

Ditto what Aaron said.
I've got a Unilite and MSD 6a running with no tach adapter.
Do a search for MSD installation, or tach adapter; and you should be able to find the wiring setup diagram. Fact is, I've got a brand new un-opened 8910 I bought just in case, and never needed it.
Mike

Yes, but...

the stock tach is current-sensing. When you remove the original coil, the switching current (points or electric points-replacement gizmo...) is now only a few milliamps. This might not be enough to trigger a tach reliably, especially an older one.

MSD's (and the Crane HI-6) provide a tach-trigger output just for this purpose. Try that first if using the original points trigger connection doesn't work for you.

It's time for my rant on the MSD 'tach adapter.' It's just a friggin' loading coil that presents an inductive load for the points just like the original coil did. My first time down this path was with an early CIS Rabbit that required a reliable tach signal to keep the fuel pump energized. I was shocked at what I saw in the box after parting with my money, especially when i had to do it TWICE because the first one (recommended by the wizard boys at Autotronic) didn't work and "Ooh, I guess you really need the high-current one after all - did we mention electrical parts are not returnable?"

I don't recall the exact loadings but the 'regular' adapter is something like 3-4Ω and the "high-current" is about 2.8Ω

If that sounds like the nominal resistance of an ignition coil - bingo... So if you've still got one in your parts stash, it's worth a try. (tape over Terminal 4...)

It's half-a-transformer, and I've always suspected that you could go to your local big-box hardware store and get a doorbell or thermostat transformer and have it work just fine - but I didn't have to go down that route so it is left as an exercise to the reader...

The 'tach adapter' can't be costing them more than a couple of bucks, copper content notwithstanding, and their "value pricing" designed to capitalize on the desperation of a car guy who needs 'just one more last bit' to get his project running rubs me the wrong way.

Or just buy a Monster tach that can run with the voltage-trigger levels that are compatible with CD ignitions... It'll fit right in the dash...

VDO tach's require at lease 125 volt voltage spike to work. It uses the back
EMF off the stock coil to work.

I just got the MSD adapter 8920 it cast me $70.00 ArtechnikA I agree with you all this money for a transformer.

I will install this week end i will post some pictures of the install I will be using the diagram posted above to install.

I Installed the MSD adapter 8920 according to the diagram above it worked PERFECT.
THANKS jasons


JC

Hello,

I just installed my MSD 6A and I cannot get the engine to run. It will only crank. I used the diagram above for the 8920 tach adapter. I unplugged everything and connected the original set up and it runs, so everything works. Any suggestions as to what I am doing wrong?

Correction 8910*

i've been running a 6A with 8910 for 15 yrs, later added an MSD timing control, with points at first, and with a Pertronix for at least 10 yrs - never any problems

I've got an 8910 new in box sitting on the garage floor. Technically, you don't need it. JCD914 helped me install mine and he just took a wire and connected it to the tach output on the MSD box and ran it to the coil... IIRC. I am putting two MSD 6AL boxes and the tach adapter on eBay today unless someone here wants it... Cleaning up the stuff I don't need..

I suppose my first question would be, are you sure the MSD box is good?
Have you double-checked all of your wiring and connections?

Mike

Where did you get the MSD box? Used?

You to start a new thread of your own next time. Old post confused with new posting, etc... Try it; You'll like it.

For some reason the stock diode with the male and female endings already crimped in place was backward. I removed the diode and the engine fired up in 30 degree weather instantly. I did not have engine run-on when I turned it off so I left it off. So I am good to go.

Glad to hear it was something simple!

That's how I have ran mine, with both silver and black dot tachs. I seem to recall that the car wouldn't fire with the adapter in, or it would run with no tach. I think I sent the adaptor to Andy for shipping. Waste of money for the adaptor. The only reason I still use it is that I paid for it. When it dies, I plan to run without.

Carlos

lol, me too. Thanks