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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53945
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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ML430: , I have a 99 ML430 and took the top of dash off

Customer Question

I have a 99 ML430 and took the top of dash off to r&r blend door motor. Now the cluster and radio illumination don't work. Bulbs and related fuses check OK. How should I diagnose?
Submitted: 2 years ago.
Category: Mercedes
Expert:  Marty replied 2 years ago.
Hi, first make sure that the panel light rheostat in the cluster is turned all the way up. Next make sure fuse 9 has battery voltage with the headlights turned on. Fuse 9 powers the dash lights through the rheostat in the instrument cluster. Power to fuse 9 comes from the headlight switch.
Let me know what you find.
Customer: replied 2 years ago.
Good and bad. First, we had already checked the Rheostat. I rechecked the fuse and it was OK. But this time I took the steering column shrouds off and checked the remaining wire harnesses to the column. When we put the cluster back in (it was out from checking the bulbs), it lights up, and so does the radio. But now the gages are acting funny. The speedometer flutters badly then settles way below zero. The gas gage is reading less than 1/4 when it has 1/2 and was reading fine. Can these be reset or did I fry the cluster?
Expert:  Marty replied 2 years ago.
I don't think you fried the cluster. It sounds like you have a poor connection at the cluster or there is a loose ground. The ground is over on the passenger side kick panel. Did you remove any ground wires over there? Also carefully check your cluster and make sure you didn't bend any pins when you plugged it in.
Customer: replied 2 years ago.
Checked the pins twice, no problem. Didn't mess with anything by the kick panel. This one just started today. It looks to me like the calibration is off on two gages (only). The Speedo reads about -5 standing still and I think is 5-10 low at speed. The gas gage is 1/4 low. All others are fine (which would say the main grounds are fine. Is there a way that only a few gages can go out of synch?
Expert:  Marty replied 2 years ago.
Try disconnecting the negative battery cable for 10 minutes and see if the gauges reset. I'd also try running a separate ground to the brown wire at terminal A3 on the cluster and see if anything changes.
Customer: replied 2 years ago.
OK, but it will have to wait until tomorrow at least. Daughter just took the car. I did disconnect the positive for at least 5 minutes and didn't change anything - is it important which terminal?Also, I was checking the connector for ground and power and was having trouble picking up any connection at A3. Was getting good ground at A12 but couldn't get my pin to contact metal in A3. So this could be it, but wouldn't that affect all the gages? And why is it rock-solid off by -5 (checked against GPS on phone from 5 to 50mph). Let me now if this gets you thinking and I will post when I get the car back. Thx.
Expert:  Marty replied 2 years ago.
It doesn't matter which battery cable you disconnect. I'd focus on making sure you have good power and ground to the cluster. That would make the most sense. It looks like the main power inputs are on A11, A7, A9 and A13. A3 is a ground. You may need to use a smaller probe to test the pins.
Let me know how you make out.
Customer: replied 2 years ago.
Hi,Sorry for the delay in ratings.I won’t have time to try your latest recommendations until the weekend. So far the information has not been helpful to fix my fluttering/inaccurate gages, but I am hoping that you are steering me in a good direction…Thanks,
Expert:  Marty replied 2 years ago.
Hi Mark, thanks for the update. I'll wait to hear from you.