bounceing tach after msd 8920 hookup?

[kully 560]

I have a early 1974 260z with e12/80 dissy .installed the msd 6a with the blaster 2 coil .could not get the tach working with the msd 8910 so I pickup the msd 8920 tach adaptor. tach works but there is a little bounce there and also when the headlights are turned on it stops for a moment. I hooked up the msd 4 wire tach adaptor as follows black ground, red 12v switch power, violet to blue wire from wire harness in car which is the tack wire, white to white wire from msd 6a and also connects to c term. on e12/80. msd is closed today . is this the correct hookup thanks kurt

Edited February 28, 2009 by kully 560

[beezee]

Take the white wire from the tach adapter and plug it directly into the tach output terminal on the MSD box. The white wire to C.

[gnosez]

If memory serves me correct the violet wire is not used in your application.

Check the MSD website for a wiring diagram.

[kully 560]

I have the msd 6a with no tach output and the violet wire I thought from the 8920 was the tach output

[kully 560]

beezee I found the tach output and tried wireing the white wire from the 8920 to it and left the msd6a white wire connected to the c term on the e12/80 .the tach works but not as good as before and now when the headlights are turn on the tach stops working alltogether.the other 2 black wires that went to the ballast resister I spliced together also.I remember when I talk to msd tech I thought they said I might need a capacitor in line that they would supply but just want to make sure I have it hooked up correct. at least the 8920 works somewhat but the 8910 did nothing at all!

[beezee]

Kurt,the symptoms of the tach not working indicates loss of power or voltage drop to the tach when the lights are turned on? Check voltage at the 10 amp instrument fuse with the lights on and off.

[kully 560]

i will check and let you know the results thanks kurt

[kully 560]

beezee I spoke to msd today and resolved the tach issue ,the bouncing or pulse issue was because they recommend on the 8920 to ground to the battery not chassy. also I had to refeed the msd8920 from another source such as not from the black/white tracer wire that feeds the msd 6a.and also feed the b term on the e12/80 dissy. it pick up pulse from the msd 8920 which caused the tach trouble.I feed the msd 8920 direct from the battery and my tach is perfect, with lights on or off.so I need to pick another source for power.I am going to pull my fuse box and detail and rebuild it for cleaner power as the oem is nla and msa says the 1973 will not fit.can not hurt as it is 35 years old. kurt

[beezee]

Hey Kurt ,glad this ones solved , grounding to the battery and another keyed power source,would be interesting to see the voltage input to MSD red and E12-80 "B" if its pulsing. Running an earlier electronic dizzy I didn,t have any problems what so ever.

[kully 560]

beezee the tech had me use my fluke meter and I read the tach output on the msd6a and it was between 2.8 volts and 3.1 volts so that told him the tach output was working fine. then I took the reading on the msd 8920 and the voltage was 14volts it was the violet wire for the tach. so that was working fine. so we spoke a little more about wireing and decided seperate feeds and seperate grounds .it works like a charm.so I guess you know beezee this made my day .but I still need to run a seperate feed as I said I tryed it off of the positive side of the battery.I will pull fuse box and detail it and hook up the seperate feed this week and let you know . the tech thinks the feed for the 8920 was spliced in to close to the msd6a kurt

Edited March 3, 2009 by kully 560

[draztik280]

I am about to buy a Blaster 2 coil for my 77 280z and replace my old stock one. My question is, by replacing the old ignition coil and replacing it with the Blaster 2 coil (w/out the MSD 6A and will just use the stock one) will improve any spark? or it is still the same spark output as the stock coil?

Thanks

[Firepower]

Hi - I understand this is an old thread, but there’s lots of relevant & useful info here.  So I’ll post here. 
as OP states, I think you need the MSD8920 to work with the early stock tachs, mine’s a ‘73 240Z.

My understanding is it’s a ‘current loop’ tach so one side  (black/wh wire) goes to the pos + on the coil.  The other side (grn) used to go to the ballast resistor (which I removed - so just straight to keyed ignition.   That is stock and works, is stable and very accurate. 

I’m installing an MSD6AL to my car, and bought that and a PCE2030 (p/n PCE387.1002) which is an 8920 type tach adapter. No instructions, just the unit. 

So far so good- but the wire colors are different from the MSD 8920 and when I contacted the supplier, they just sent me to the MSD diagrams and said it was ‘the same’.  But the wire colors are not.  MSD8920 has Red, Black, Violet & White. 
I have 4 wires on the PCE tach adapter I bought: Red, Black, Green, Orange  

I think I end up with the Red wire on the Tach adapter at the Grn wire of the tach, and so on to switched ignition. That’s all I’m sure of. 
There is No white wire on the “8920” unit I bought.  
Anyone have a wiring diagram or can help?

Nothing but orange/black from the MSD6AL will end up running to the coil, so the existing tach black/wh wire has to move.

Thanks.