w126 1986 300SDL -- no dash lights - PeachParts Mercedes-Benz Forum

daw_two · #1 11-03-2007, 12:08 AM

So, Brian. Are there 2 circuits within the rheostat? I'll give it a whirl after I replace the 5watt bulbs with 3watt bulbs in the morning. And one of the prisms looks browish --- have to wonder if my lights are going to look brown.

Thanks for the quick reply.

Brian Carlton · #2 11-03-2007, 12:13 AM

Quote:

Originally Posted by daw_two

So, Brian. Are there 2 circuits within the rheostat? I'll give it a whirl after I replace the 5watt bulbs with 3watt bulbs in the morning. And one of the prisms looks browish --- have to wonder if my lights are going to look brown.

Thanks for the quick reply.

The rheostat is a single circuit in series with the dash lights. I'm trying to see if you have power at the rheostat, and then bypass the rheostat to eliminate it from the circuit.

daw_two · #3 11-03-2007, 12:45 AM

Quote:

Originally Posted by Brian Carlton

The rheostat is a single circuit in series with the dash lights. I'm trying to see if you have power at the rheostat, and then bypass the rheostat to eliminate it from the circuit.

the rheostat dims and brightens the outside temperature display.....so, it must be working, right?

EDIT: While I'm in here, I might as well try to make the RESERVE light work on the fuel gauge work, too. Should it come on initially like in my 300D when the key is turned to position #1? What watt bulb is that tiny thing?

Thanks!

Brian Carlton · #4 11-03-2007, 09:30 AM

Quote:

Originally Posted by daw_two

the rheostat dims and brightens the outside temperature display.....so, it must be working, right?

EDIT: While I'm in here, I might as well try to make the RESERVE light work on the fuel gauge work, too. Should it come on initially like in my 300D when the key is turned to position #1? What watt bulb is that tiny thing?

Thanks!

Yes, that confirms that the circuit is functioning, so, you can forget about any fuse or rheostat issues.

Your problem is the bulbs and/or the sockets.

The reserve light doesn't work because of the accumulated debris on the fuel sending unit.........most likely..........and you'll have to remove the rear seat and pull that unit (need a big socket) and clean it with Brakekleen. That will restore function of the reserve light.

daw_two · #5 11-03-2007, 09:55 AM

Quote:

Originally Posted by Brian Carlton

Yes, that confirms that the circuit is functioning, so, you can forget about any fuse or rheostat issues.

Your problem is the bulbs and/or the sockets.

The reserve light doesn't work because of the accumulated debris on the fuel sending unit.........most likely..........and you'll have to remove the rear seat and pull that unit (need a big socket) and clean it with Brakekleen. That will restore function of the reserve light.

So, Brian, are you saying the reserve light will NOT come on when the key is in Position #1 because of the accumlated debris? This is interesting. Would biodiesel help dissolve this debris? My 300SDL was run on a biodiesel blend by the PO and I've been running B100 for past 4498 miles. So biodiesel doesn't help?

Also, on my 1985 300D, the reserve light comes on in Position #1, then goes off after car is started.

Different beasts?

Thanks again for your assistance.

I have about .45 volts to pin #5 of the 15 connector socket. I'm going to replace the bulbs with 3watt and see what happens --- maybe the melted plastic has contorted the sockets so they aren't making contact on the little strips around the edge of the hole. Fasinating way of making a connection. These cars continue to amaze me.

Brian Carlton · #6 11-03-2007, 10:11 AM

Quote:

Originally Posted by daw_two

So, Brian, are you saying the reserve light will NOT come on when the key is in Position #1 because of the accumlated debris? This is interesting. Would biodiesel help dissolve this debris? My 300SDL was run on a biodiesel blend by the PO and I've been running B100 for past 4498 miles. So biodiesel doesn't help?

Also, on my 1985 300D, the reserve light comes on in Position #1, then goes off after car is started.

Different beasts?

Thanks again for your assistance.

I have about .45 volts to pin #5 of the 15 connector socket. I'm going to replace the bulbs with 3watt and see what happens --- maybe the melted plastic has contorted the sockets so they aren't making contact on the little strips around the edge of the hole. Fasinating way of making a connection. These cars continue to amaze me.

Well, nothing is for certain, but, on two of these, the gunk at the bottom of the sending unit created circuit problems for the light. No opinion as to whether Biodiesel will cure it.

Both the '85 and the SDL function in an identical manner. The light comes on in position 1 and is extinguished when the vehicle is running. It will come on again when there's about 3 gallons remaining in the tank. I'm not sure if the accumulated debris will affect the test in the original #1 position. It's certainly possible.

I think you are correct with the distortion on the socket holes.

daw_two · #7 11-03-2007, 03:51 PM

I have working dash lights that actually dim with the rhetostat!!!! I trim a little bit of plastic on the back (or bottom) of the plastic surround on the outside edges of the inner piece. I also painted the brown (from over heat) plastic a nice bright white. I replaced the bulb in the RESERVE light indicator but it is NOT coming on when the key is in Postion #1. Oh, well, that was going to be a bonus anyway. Maybe at some point it will start working.

At least, NOW, I'll be able to see how FAST I'm going on my upcoming road trip --- the first time I've been able to drive on the interstate for more than an hour.

Time to tackle the radio antenna and the gasket around it.

Thanks, everyone, for documentating all the work in front of me.