I recently installed a summit ignition box with rev limiter, and my auto gage tach wasn't compatible. I then bought MSD part number 8920 to correct the issue, but no luck. My tach is from '99, the tech guy at summit said all I needed was the tach adapter, but someone else told me that the older auto gage tachs aren't compatible. It worked fine before.
If someone could tell me which company to go with that would be great, i'm a little disappointed at the trouble I went through for a rev limiter, but the ignition box is nice. I was looking at the summit tachs for like 60 dollars or a sunpro one for 100. thanks

 

What is the part # for the box?

I have an older MSD 6A that is compatable with the Autometer, and Autoguage tachs, (old and new) and the new 6A that I just bought says it's not compatable with the Autoguage, but is with the Autometer.

I hate to say this but you may need to buy a new tach.

I see that you've been looking at the Sun Pro, and the Summit tachs. But wouldn't you definately need an adapter with those brands? I would thinks so.

 

I'm trying to sell the tach in the classifieds. I think it's pretty ridiculous what I went through trying to get it to work. I posted back and forth in an MSD forum, they gave me a bunch of tests to do on the 8920, and it didn't pass one test, yet the idiots think it's the ignition box? Does that make sense to you?
I mailed the 8920 to them yesterday. I also talked to a tech guy at summit, I asked him twice what voltage I should see at idle on the tach output, and he ignored my question. The # is 850600 I believe. The MSD tech thought my box was messed up, because I should only see 1-5 volts at the tach output, but why would my stock tach work. The original HEI was good up to 7k, I don't think i'm going to buy a CDI box ever again.
If I need the adapter I already bought it, so i'd like to buy a tach that needed the adapter, so I don't throw out my $50 plastic box from MSD.

 

I had no problem with the box from summit giving the proper signal to the factory tach, which I didn't expect at all due to the whole berlinetta digi dash. I also have this box on my truck, and no adaptor was needed for the sun pro tach. I would return the MSD tach adaptor and get a new tach, the box is fine and much improved over the stock ignition espacially with a rev limiter.

 

There's no returns on electrical parts, I sent it to MSD. I'm going to get a summit tach most likely and mount it on the steering wheel.