Well I just went through this. I had a partially discharged battery two weeks ago, not enough juice to start the car, just click, click.... I charged the battery for awhile but it wouldn't hold the charge and I "jumped" it to go to AutoZone for a battery. Somewhere somehow, the voltage spike caused the microprocessor to be damaged. My symptoms were slightly different. NO Tach and No Speedo. All other gauges worked including trip OD, the OD, and the MPG gauge and my cruise control all functioned. My top controller worked.

If you haven't checked the fuses on the passengerside, underneath the cover for the computer boxes, check them. There are four. My fuses were intact as were all other fuses in the car.

I was told by BBA Reman in Taunton, Mass. that my cluster was not rebuildable because there are no processors available. It cost me $17 in shipping to find out it was fried. Another place to try is Andy at DNA Speedo repair in Tampa. Very knowledgeable and helpful. 1888-495-2777. I have a 95 SL500 and it had the digital cluster. I found one within a half hour drive to my house in Cleveland Ohio. This guy (Sam) has another cluster with a cracked lens. My original plan was to buy it and switch the lenses from mine. However, when I connected the cluster, the speed was off, like it was reading a V6 instead of a V8. When I was traveling 25 it read 40 and so on... The tach worked fine though as did all the other gauges in the cluster. I lucked out, the second cluster he had worked perfect and it was like new. By the way, I have my SL up for sale and I have lots of extra parts if you need any down the road.

In summary, you might have a blown fuse in the computer area, or the cluster might be fried like mine. BUT Andy at DNA said he could fix most speedos but maybe not the Tach. So I would try either place or even both.

Good Luck, Steve fazekasstephen@gmail