During this extended down time I spent some time downloading runs from last Sept. when I had issues with lost MPH.....5-6 off and never found anything mechanical.....

I have a Grid controller connected to an older MSD 7al3 (red box) and have used that system for 5-6 years

During my day of chasing the lost MPH I replayed my Autometer tach and rpm was showing only 100-200 low....mph was off from usually 173-174 or better in cool air to 166-167

I had never viewed those runs until today on the Grid.....It shows RPM to be down more than that and appears as if the rev limiter is on....the same look as when on 2 step on starting line...

Normal rpm at the stripe is 7300-7400.....Grid recording showed 6800-6900


I hooked up my MSD tester and can fire the ignition and it runs without any issue to any rpm....BUT my Tach does not work and if I trigger any rev limiter nothing changes

It all works normally whan I run the car without the tester....

I went over the various wire connections and see nothing......Grid to MSD....connections to K&R Panel and switch panel....nothing wrong.

I've used the MSD tester before on other cars....Tach worked....and I was looking to see if my burnout chip was active downtrack....it is a 7000 chip...and that would kind of make sense..


I know I'm rambling here but that is the best explanation I have for it all...

Markemark is the man with the best knowledge on all the MSD products....I did the lastest upgrades to the box and have the latest versions of View and Review....

I'm not looking for responses about your car did this or that so thats what my car must be doing.....

Why does my Tach not work using the MSD tester and why do my rev limiters also NOT work using the MSD tester...launch, burnout....and high side...


3 runs that were very consistent and dialable and nothing mechanically wrong....and MPH off and nosed over at the same point every run.

My old brain dead arse could not tell if it was indeed on the revlimiter.....maybe it was....

Does the grid data actually show the limiters being active or it just looks like the limiter is applied?

I'm not using the Grid for rev limiting...

Chips in the 7al3 so the grid has no control of rev limits

The instructions said rev limiting using the grid with a 7al3 would be harsh and to use chips.....None of the grids rev limit trigger wires are connected....

Don't know if this is your problem but the tach circuit went bad in my MSD 6-T and MSD even admitted that it was bad. They repaired it and the box went back to working perfectly. Just thinking that if your tach circuit in the box is bad that might be the reason. Good luck!

I was hoping I found my issue from last year but could not confirm it using the tester.

Multiple items in the car all interconnected make it more complicated....

Under normal running conditions the Tach works fine. But I'm not sure about the rev limters.....

Was just hoping the burnout limiter was active possibly from a bad microswitch......I'd never know it until the engine got up to that rpm down track....

I need to do more investigating but am dumbfounded as to why when I use the tester the tach does not read correctly and the rev limiters don't activate...

I'm trying to decide whether to go all Grid or replace the 7al 3 with a new black box...

I'm leaning to all Grid now that I have my laptop working well and totally up to date on the grid software.

Which device is connected to the tach input signal.. 7al3 or Grid ??

The Tach output terminal on the 7AL3 is empty

The Grid controller grey wire is connected to the Tach terminal on my K&R fuse/relay panel...

I did not wire the car but did install the Grid....The Tach has always worked and so does the rev limiters using chips in the 7al3

I tried adding a jumper from the 7al3 Tach terminal to the K&R Tach terminal and nothing changed....

I Have the large laminated sheet for the K&R switch and relay panels and the connections to the ignition and all other devices....

I never had an issue like this in the past using the MSD tester....The coil fires flawlessly to any rpm with or without a rev limter triggered as it sits...using the MSD tester...

The Grid does record rpm and the green light flashes rapidly when the ignition box is running....tach works normal when engine is running...

Quick question semi related, what tester do you have ? I need to purchase one and see 2 listed. They are very similar. Thank you

This message has been edited. Last edited by: 27Keith,

I am not familiar with the grid but I know those red 7AL3's can be evil! Just food for thought.

For some reason there is an electron shift in the universe the last few days and it's zoned in on me, my car and this computer now too....

I usually use the Edge browser in Windows 10....did the conversion from 7 earlier this year and it all worked fine until a day or two ago

Out of nowhere I can no longer post on here using the Edge browser....

Chrome works...Edge does not....I did nothing that I'm aware of to cause the issue.....OH well

Lets get back to the ignition and testing.

Today after half a day at work.....

I removed the grid controller and hooked the Red 7Al3 up as it would be without the grid.....NO CHANGE with tester....Tach does not work and rev limiters don't activate...

I verified the wiring and voltage signal to trigger the rev limiters and checked the chips.....Nothing wrong.....

This car has sat since last September until I rebuilt the engine and have had it running in the car last month and the Tach was working then....don't know about rev limters...

I added a crank trigger and ran the engine using both the crank trigger and then the mag pickup in the distributer.....1 degree differnce in timing doing nothing but disconnecting one and connecting the other...

The red box is out and I would not waste my time or money sending it to anyone.....it's from 2003....never had any luck sending anything to MSD....I'll send it to the garbage can.....

I believe the burnout limiter was active last September on 3 successive runs....and now it appears the box lost the Tach output signal.....

I work with electronic controls, devices, boards and it's no shock to experience odd things but this one dragged on for more than 6 months, MY FAULT there because I was looking in the wrong place...

The Grid ignition component will get installed along with the recommended coil and fix up some wiring......

It's not like we're going racing anytime soon !! NJ's governor is about 1 step away from declaring Marshall Law.....Pretty much can't do anything and it ain't changin anytime soon....


So Al I agree my red box is evil now and it has 2 MSD stickers on it. The previous car owner must have sent it in twice.....Not me.....It did work for me since around 2007 with no issues.....