tachometer question

[eddie102870]

have a dash just rebuilt by Justdashes. running a MSD 6AL and Mallory distributor on it. not getting anything from the tach output on the box. any ideas?

 

[dadsbee]

OE tach in the car.. won't work with electronic spark boxes. You need an "adapter" for it, from what I've read anyhow. I still run points..

 

[eddie102870]

just got off the phone with MSD. you are correct. thanks for the reply.

 

[kiwigtx]

You need one of these.....

https://www.msdperformance.com/products/accessories/tach_adapters/parts/8920

 

[eddie102870]

ok bought the tach adaptor and still no dice. cant figure this out. any ideas why this wont work

 

[dadsbee]

Did you tach work pre "justdashes" panel rebuild?

 

[not so famous bob]

You need one of these.....

https://www.msdperformance.com/products/accessories/tach_adapters/parts/8920

View attachment 594249

I AM NOT AS SMART as a bunch of guys on here, but I have had MSD`s on 4 diff cars, and have never needed one of those.
1 hemi , a 383 vega , a 406 vega , a 406 gmc , and now a 505" wedge 68 fastback. WONDER WHY ?????

 

[Billccm]

A tach is a voltmeter with an integrator. Basically it converts pulses to a steady voltage. The more the pulses, the higher the voltage.
If your tach is dead, then it's either defective, or not getting any pulses. The tach adapter is a pulse stretcher and voltage divider to take the multi pulses and convert to one pulse.
My point is even without adapter your tach should read if it's receiving pulses. It would just read incorrect rpm.
Let us know what you discover.

 

[not so famous bob]

A tach is a voltmeter with an integrator. Basically it converts pulses to a steady voltage. The more the pulses, the higher the voltage.
If your tach is dead, then it's either defective, or not getting any pulses. The tach adapter is a pulse stretcher and voltage divider to take the multi pulses and convert to one pulse.
My point is even without adapter your tach should read if it's receiving pulses. It would just read incorrect rpm.
Let us know what you discover.

Mine have all been right on 5 diff cars ! ???????????? There have been situations in all the instructions that came w/ the new units, that had that adapt available if a certain problem arose w/ the tach not reading right, but I have never had the need for one. My 505 has a fast 2.0 fuel inj system, and the cheap tack I have is w/in 75 rpm of what the handheld says, which is right.

 

[dadsbee]

Did you use the MSD tach output connection, or where you still running points and used the - on the coil terminal?

 

[eddie102870]

had it rebuilt by just dashes. i bought the car torn apart, cluster didnt have a tach. i added that to it. i hooked it directly to the tach output with nothing. hooked it up with the tach adaptor and still no juice. just wondering what i could be doing wrong.

 

[dadsbee]

Got a power wire on it?

 

[eddie102870]

Got a power wire on it?

i do.