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Thread: Indicator Light Problem 1992 500E

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    Indicator Light Problem 1992 500E

    I have recently experienced a problem with the oil indicator light flashing on and later going off. Now, I have the reserve fuel light on even though the tank is half full. Finally, the antenna is only working intermittently. The oil level is topped off and the sending unit on the fuel cell is relatively new. Also, the upper wiring harness has been replaced. Is there any possible common wiring issue linked to these electrical problems or is it more likely that they are all individual problems to investigate. I am not sure whether the lower harness has been replaced, so I am wondering if this could be related to all the lights coming on and the antenna's inconsistent operation.

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    Re: Indicator Light Problem 1992 500E

    No correlation between the upper wiring harness and anything with the gauges/indicators, at all. Same with the lower wiring harness and anything relating to the antenna and fuel sending unit. The lower wiring harness could have something to do with the oil level sensor tripping the light.

    This sound to me like a ground or connection issue more than anything.

    I would start by doing the following:

    1) open the fuse box and rotate all fuses in their holders. Better yet, replace with Flosser ceramic (brass or copper) fuses. I would specifically check/replace fuses 3, 5, 9 and C
    2) remove the instrument cluster and check all grounds and connections on the back of it. Check the ground point behind the instrument cluster

    Fuel sender at the tank could be wonky, causing the false alarm, although you said you replaced it, so I HIGHLY doubt the sender is the problem.. Is the fuel gauge needle accurate, and just the reserve light going on with the needle being OK? Or is the needle flickering too?

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    Re: Indicator Light Problem 1992 500E

    Thank you for the checklist. I am going to look into it today. On the fuel gauge the needle is steady and I am fairly certain it is reading accurately. I am suspicious that it may be a ground on the back of the instrument cluster as I removed it over the winter to replace the odometer gears. I will check the fuses first. Thanks again.

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    Re: Indicator Light Problem 1992 500E

    Well after some more investigation, I found that the fuel gauge is stuck at half tank even with no power. So, the possibility is that the low fuel indicator is on because the tank is lower than I thought. I will add some fuel this week and see if the light goes out. I am not sure if the fuel gauge can be replaced or repaired. Any ideas? I checked all of the fuses and everything is making contact. I plan to check the oil sending unit and the antenna as each problem seems to be separate. Does anyone know the location of the oil sending unit? I might also have a voltage drain scenario as the battery was discharged yesterday.

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    Re: Indicator Light Problem 1992 500E

    The oil level sender is located inside the engine block, and requires dropping the lower oil pan to access. The O-ring is a common leak point so if it's never been done, a new sender (Hella, ~$50 or so?) is not a bad idea. Should be a thread or two on the forum discussing this in more detail.

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    Re: Indicator Light Problem 1992 500E

    Sure sounds like a potentially bad ground, or perhaps failed solder joints somewhere on the fuel/oil/temp gauge assembly. If you remove the gauge from the cluster, you can test the gauge with sime pointers here —- simulating various resistances should tell you if the gauge is reading properly, thus allowing you to isolate if the prob is w the gauge or with the information that the gauge is receiving (like the sender, wiring, etc.)

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    Re: Indicator Light Problem 1992 500E

    Erratic operation of the low oil level indicator can also be a function of its controller board, which is located in the instrument cluster. As the electrolytic capacitors on the board age and dry out, their values drift, affecting the timing function of the circuitry. The circuit effectively “watches” the ground signal from the sender, and if it is maintained for more than a fixed period of time (in seconds) the light will light up. When the timing function gets wonky from the capacitors aging, the light can come on and off intermittently, or even stay on for a period of time.

    As this is a function of the circuit board and not the sender, even disconnecting the sender will have no effect on the operation.

    The fix? Remove the circuit board from the instrument cluster and replace the electrolytic capacitors.

    Dan

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    Re: Indicator Light Problem 1992 500E

    Dan brings up a good point. The low oil level indicator is not supposed to illuminate unless the sensor has been triggered (due to low oil) for 60 seconds. When the light goes out, it should NOT come back on for at least 60 seconds. If it does... the timing circuit is not working. As Dan described above, this can be fixed, and the issue is with the gauge itself - not the sending unit.

    If there is 60+ seconds between each time the light comes on, that could be the sending unit, or the lower harness insulation deteriorating. Since your lower harness may be original, this could be difficult to test, although you can still try testing via the FSM procedure attached (section B and C).

    Attached Files Attached Files

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    Re: Indicator Light Problem 1992 500E

    Excellent information. Thanks to everyone. The light is going on and flickering in some instances for less than 60 seconds. In other cases it is going out for longer than sixty seconds. It sound like it could be a problem with the capacitors or the wiring. I have some diagnostic work to do this weekend! Thanks again.

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    Re: Indicator Light Problem 1992 500E

    I wanted to point this out, as I have a 1997 R129 in the fleet with this setup and it was totally flaky to the point where I removed the lamp from the cluster until I could fix it so the spousal unit wasn’t freaking out about losing all the oil in the engine (which wasn’t happening, of course.)

    Dan

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    Re: Indicator Light Problem 1992 500E

    Quote Originally Posted by LWB250 View Post
    I wanted to point this out, as I have a 1997 R129 in the fleet with this setup and it was totally flaky to the point where I removed the lamp from the cluster until I could fix it so the spousal unit wasn’t freaking out about losing all the oil in the engine (which wasn’t happening, of course.)
    She sounds like a keeper.


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    Re: Indicator Light Problem 1992 500E

    Quote Originally Posted by gsxr View Post
    She sounds like a keeper.
    Yeah, after 38 years I’ve got her trained to kill the engine and coast to a stop if the car loses oil pressure. Guess I’ll keep her. The car, too.

    Dan

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    Re: Indicator Light Problem 1992 500E

    I had a few minutes to check some things out today. The fuel gauge was still stuck on half tank with the reserve fuel light on. I disconnected all wires from the instrument cluster and the fuel gauge went to empty. Reconnected the wires and fueled up the car. It took 22 gallons so it was obviously empty. The reserve fuel indicator light went out but the gauge remained on empty. After driving home, I disconnected the wire at the fuel sending unit and reconnected it. The fuel gauge went up to 3/4 full. So, the good news is that the reserve indicator light is working correctly but the gauge is not reading accurately. I had the sending unit replaced about 6 months ago so I do not think this is the problem. I am wondering if the gauge needs to be recalibrated to match the new sending unit. If the rain holds off tomorrow I am going to run some of the diagnostics GSXR sent on the low oil level indicator.

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    Re: Indicator Light Problem 1992 500E

    There is no calibration necessary or available for the fuel gauge and sender. The values are fixed and designed specifically for the circuit. Any "trimming" of the circuit is done in production by altering fixed resistances at the gauge itself.

    Based on the issues being centered around the instrument cluster, I would be looking at the connectors on it as well as the ground point that is immediately behind it in the dashboard.

    While I hate to mention it, when was the last time you cleaned or replaced fuses, and are you using the quality copper fuses or aluminum ones? Visual inspection will reveal their composition.

    Dan

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    Re: Indicator Light Problem 1992 500E

    The fuses have just been cleaned and rechecked. However, I think I figured out the problem. I put light pressure on the circuit board on the top left behind the fuel gauge with the instrument cluster partially pulled out and the gauge went to full. When I turned the engine off the gauge stayed full. Some light pressure on the same area and the gauge went to empty. I started the car gain, put some pressure in the same area and fuel gauge reading went to full and the oil light indicator went out and remained out. It seems like I have a cold solder joint. I noticed there is a brown wire that solders at two points. It is about 1/2 inch long. I am going to re-solder and see if this solves the problem. I am wondering if this is a ground point on the circuit board.

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    Re: Indicator Light Problem 1992 500E

    Okay. Re-soldered connections and the fuel gauge is working correctly. The oil level light came on again, so I will follow up with the diagnostics on that item tomorrow.

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    Re: Indicator Light Problem 1992 500E

    A test of the oil level sensor gives a reading of 0L. Based on my understanding this would indicate the sensor is open and needs to be replaced.

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    Re: Indicator Light Problem 1992 500E

    Not to sound like it's a stupid question, but is this with the sensor in place and the engine full of oil? If so, it should read as an open circuit. Just trying to clarify the conditions under which you're testing it.

    Dan

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    Re: Indicator Light Problem 1992 500E

    Yes, the sensor is in place and the engine oil is full. Test B in the PDF file sent by GSXR indicates removal of the connection from the lower wiring harness and measuring the resistance from the tip of the sensor to ground. If I am understanding correctly, the value should be less than 1 ohm. I must be missing something. I also checked the condition of the lower wiring harness and the condition is poor. There is no tag on the upper side of the harness. The only date I found was on the small wire connecting behind the box on the passenger side. The number is printed on the insulation and looks like a date, 31 1 91. I suspect this is the original lower harness and needs to be replaced. I noticed there have been threads indicating the lower harness is NLA. If I have the correct part number, it looks like it can be sourced from MB oem parts for around $282.00.

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    Re: Indicator Light Problem 1992 500E

    Quote Originally Posted by ffinn View Post
    The only date I found was on the small wire connecting behind the box on the passenger side. The number is printed on the insulation and looks like a date, 31 1 91. I suspect this is the original lower harness and needs to be replaced. I noticed there have been threads indicating the lower harness is NLA. If I have the correct part number, it looks like it can be sourced from MB oem parts for around $282.00.
    There are usually 2 dates on the tag. The earlier date is the design date, the later date is the manufacturing date. If the latest date is still early 90's, yup, it's original and should be replaced. More info in the Wiki here:
    https://www.500eboard.com/forums/wik...Wiring-Harness

    You will need to contact a dealership in person to find out if it is still NLA (i.e., permanent NLA, not just on backorder). Placing an order that will likely get cancelled, by multiple different vendors, is a waste of time. Please read this post for more details:
    https://www.500eboard.com/forums/showthread.php?t=12376

    On the bright side, Jono rebuilds them equal or better than new... shoot him a PM or contact him here: http://blueridgemb.com/child/contact.htm


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    Re: Indicator Light Problem 1992 500E

    Fantastic. Thanks gsxr.

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