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MSD 8910 tach adapter
A friend brought me a MDS system 6429 box and the 8910 tach adapter. Car runs fine but no tach. It's a 78 3.0 engine in a 73 body. I called tech support at MSD and they said the adapter needs to be the 8920. I know this is not correct because I saw this set up working in the car he got it out of. So, there is a white, and a red wire on the tach adapter, so where do they hook up to?
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Tach adapter
I have an 8920 on my 80 sc and it works fine. I used the diagram I got online at MSD.
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Rick,
An 8910 is a doorbell transformer in a plastic box. Really. This is a very electrically dirty way to drive the tach, but it works- but usually if you have a pre-october 1970 tachometer. The way it works is that the coil has one leg connected to +12v, and the other leg connected to the points. The /1 input to the tach is connected to the points also. When the points close, the coil charges, just like an ignition coil. When the points open, a big whopper of an EMF fires up the tachometer black/purple wire and slams into the tach, where it triggers the tach's monostable multivibrator circuit-- basically a voltage pulse that triggers a transistor to shut off. Some guys use a diode in line to damp down the ringing of the coil, but that's an elegant solution. This tends to burn up the points just like old-school kettering ignition but it works. Anyway, I don't know what a 6429 is, can't find that part number, but if it's a 6AL, why not just use the tacho drive terminal, a 1/4" terminal on the side of the box, to drive the tach? What tach is in the car? What numbers on the back? What date code? |
I have a brand new 8920 still sealed in the factory packaging and I need an 8910 if your friend wants to swap.
- Justin |
Admittedly self-promoting here, but if the MSD Adapters don't work out for you, please consider trying one of my TACH-ADAPT units. This unit has helped solve similar problems for many members on this forum. Home Page
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Quote:
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date stamp on the tach is 4/72.
The nay sayers all say to buy the tach adapter right out of the gate. That is why I didn't try the spade on the MSD . John, it was a typo on the MSD unit, it is a 6 AL 6420, not a 6429. Monday morning I am back it. Time to go home for the weekend. |
i have run one for 15 yrs - no problems
there is another recent MSD thread you should search & read on this site . |
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