If you're interested in resetting your speedo for larger tires and such follow this link: http://www.tbichips.com/drac/

That link doesn't quite tell you where or how to find your ECU though. That's what this How-To is for. The ECU in a 1st gen blazer will be illustrated in this article.

Your ECU is located roughly here, behind the glovebox:


It cannot be gotten to through the glovebox however, as I found out, and you must go in from underneath:


First, you must remove this panel. It is the panel in front of the passenger side door. there should be 4 screws holding it in:


There should be about 6 screws holding this bottom trim piece on located about here:



I found this trim piece to be pretty flexible. You WILL have to flex it some to get it out. It would be a good idea to keep your eye on that massive wire loom and remember where it was before you take out the trim piece as that wire will get in your way during re-installation.

After removing that piece, all the work is done you should see a silver tab under the glovebox with a screw holding it in:



That plate holds your ECU. To get it out, simply take out the screw and push back while pulling down on it. It may take a couple tries to get it out. Be careful! This piece is static sensitive! Try not to touch any of the bare connector wires or terminals. Hold only the case. Attached to your ECU is the unit you need to calibrate your speedo. Two screws and two connectors hold it in place.

Installation is the reverse of removal. The hardest part for me was getting the trim piece from under the glove-box back on. It would be a good idea to make sure your speedo is calibrated to where you want it before you put everything back together. Just take your time and this isn't a very hard thing to do! Good luck

 

I hear ya! After I get my gears, I'm gonna get this done. Pretty good write up. I'm gonna wire up a tachometer here soon, so I'm gonna be in that area anyways.

 

Just an FYI, some models have the DRAC built into the gauge cluster. I haven't found a definitive rhyme or reason to this, but I know it is true. But it is modified in very similar fashion.

 

I realize there isn't much to this how-to but I figured this might help some member who's on the fence deciding if they want to do this or not. Just showing how simple it is. Honestly, the hardest part is soldering the switch.

 

Note to add, not all of us first gen guys have that either. I think they started that drac mess sometime around 90. My 87 still uses the tired and true gears.

 

If we can come up with a year range for this, I'll happily add it to the title instead of 1st gen. I hadn't even thought of that Neo. Thanks for pointing that out.