# MSD 6AL 6420 tach connection



## anthony2 (Aug 6, 2016)

Hi all. My first post...

I have recently bought a 69 GTO that has had a 455 put in it with MSD ignition 6AL 6420. The hood tach was flicking all over the place. It appeared that the tach connection from the msd box went back out to the distributor/coil 
area (didn't trace it fully, hard to see but i assume it was the msd blaster coil thing), then back to the tach. Looked like 2 wires were involved. I undid that connection and instead ran a wire direct from the msd box tach output to the tach. 

The tacho works fine now, but I want to know from the experts if this is ok. Is it safe? And does the wire from the msd box to the tach require an inline fuse?? Like I said it's working fine, but I don't want a problem or a fire! I'm new to this so apologies if this is a stupid question


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## anthony2 (Aug 6, 2016)

So anyway, I put an inline mini blade 10amp fuse on it.


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## 1968gto421 (Mar 28, 2014)

If you connected your tach wire to the tach wire outlet on the MSD box, you should be fine. The fuse is unnecessary since the Box regulates the amount of electricity going to the tach, but it won't hurt and will give you piece of mind.

Here is a link to the MSD 6420 instructions if you don't already have them:

https://www.jegs.com/InstallationInstructions/100/121/121-6420.pdf


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## anthony2 (Aug 6, 2016)

Thanks mate. 

Unfortunately I discovered a new problem today... the tach works to about 2200rpm, then flicks back to zero. Also goes back to zero during hard acceleration. And it flicks (as though it's losing power) to the beat when the turning signals are flicking! I tried going back to a straight wire without the inline fuse from tach output on msd box to tach, but that didn't fix it. 

I read on another site where people had spliced in an ignition-linked power wire to the tach wire to fix a similar issue. Thoughts? 

Cheers, Anthony


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## 1968gto421 (Mar 28, 2014)

anthony2 said:


> Thanks mate.
> 
> Unfortunately I discovered a new problem today... the tach works to about 2200rpm, then flicks back to zero. Also goes back to zero during hard acceleration. And it flicks (as though it's losing power) to the beat when the turning signals are flicking! I tried going back to a straight wire without the inline fuse from tach output on msd box to tach, but that didn't fix it.
> 
> ...


Haven't been plagued by that problem so am at a loss to advise on it. Hopefully someone on here with more electrical experience will chime in.

(If no one chimes in a day or two, you could try posting here on the PY forum as someone there will surely know.)
Pontiac - Street - PY Online Forums

Luck!


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