280SL Electrical Issue

[MSmith]

1970 280SL - I just reinstalled instruments back into the dash. Everything looks great, except no electrical for all items on circuit (fuse) 5 - turn signals (right and left), back-up lights, fuel gage, stop light and brake indicator.  I replaced turn signal and other bulbs with LED, all lights spedo and tack and clock work fine. I did read all related old post, no help there... fuse is good, replaced fuse (no change), seems like return is floating. I remember connecting spedo and tack returns to the back of the instruments, but I did not connect a return for the  instrument cluster (is there one and I missed it?). Any thoughts on what I am missing, steps in isolation of cause.
Thanks and enjoy Sunday football. Go niners..

[ja17]

Check the main plug connection for the wiring of the center cluster (under dash). You might have even mixed the center cluster wiring with the plug for the turn signals.

[Pawel66]

Here are the pictures of the main (hand shake) connector for instrument cluster (inside and outside) that ja17 is referring to:

https://www.sl113.org/forums/index.php?topic=22075.msg157660#msg157660
https://www.sl113.org/wiki/Electrical/Rheostat

Fuse 5 gets power inside the fuse box. No power at all on fuse bracket present? Neither side? If all power receivers of fuse 5 are not getting power - looks to me like maybe a central topic: fuse not sitting well in its bracket, wires disconnected from connector under the fuse box, connector broken at fuse box... you might have pulled something too hard while working.
There are particular wires going form the connector to each receiver, I think they should not influence each other unless fuse is blown.

[MSmith]

Thanks for the reply! I will disconnect and inspect the instrument cluster handshake connector (maybe I have a pushed pin on the connection and not making contact), I did not disconnect any other connectors under the dash. Thanks again for thoughts. I will let you know if demate, inspect, mate fixes my problem. Happy Sunday! Mark

[MSmith]

I disconnected the connector and inspected the male hand shake connector at the end of the cable coming from the center cluster, wires to each pins looks good. Remated and problem remains the same.
Any thoughts on next steps.

Thanks for the help so far.
Congrats to Chiefs, awesome game!
Mark

[MSmith]

Update I have power both sides of fuse 2-6 with ignition turned on.

[Pawel66]

Modified posts a bit: reserve light and gauge are different circuits, same fuse.

If you did not mix handshake connectors for instrument cluster and for turn lights - ok (we do it more often than it would seem).

Well, then if all receivers of fuse 5 have no power, the next point on power supply path is the wire connection under the fuse box. Then power supply for each of the receivers (pins in the harness side of the handshake connector for reserve light/gauge and for brakes fluid light and rear lamps for back up and brake lights).

This is how I would go about it.

Also, just a minor point as I am sure you checked it, but sometimes we do not notice these things: turn signals may not work when you just put LED there, I believe. Important to switch ignition on when checking stop light and back up light.

Wrapping up:
- if no power for sure in any of the receivers - wires at the fuse box maybe
Or, if looking at the receivers one by one:
- fuel gauge - handshake
- turn lights - may not work if just LED bulbs installed
- brake light and back up light - ignition on and if not working - perhaps a ground at lamp issue (outwards of lamp, a screw in the chassis where fender meets tail).

[MSmith]

Thanks Pawl,
Handshake connector is OK, not mixed up with other connector next to it.
I am not sure how to get to power supplies under fuse box...I need to look at it a bit more...but before I go there is there a way to look into the handshake connector female pins from the fuse box to see if the issue is between fuse box and handshake female pins or on the other side between the handshake male pins and central instrument cluster.
Looking at the  handshake connector female pins with following nomenclature pin 1-6 facing front of the car reading left to right, pins 7-12 facing rear of the car reading left to right I have the following observations. Power to pin 12 with ignition on, power to pin 1 with light switch on, No power to any pins with right or left turn signal on. No power to any pins with brake pedal pushed down. 
Really appreciate your help!
With this info ..any thoughts on next steps.
Thank You.
Mark

[awolff280sl]

Weird things happened when I replaced nearly all of my bulbs with LEDs.
I did it in one fell swoop and had to go back and replace many of them with incandescents, and then replace with LEDs one at a time.
Turned out that all four of the turn signal LEDs required resistors before they would play nice.

[Pawel66]

I have not practiced it myself, but there are numerous posts explaining that for the turn signal breaker the bulbs need to provide load for it to work. LED do not provide this load. I do not know what exactly the symptoms are, but turn signals may not work just with LEDs with no resistors. For the same reason as when you put in 21W bulbes vs. original 18W, the turn signal will be blinking slower. When one bulb goes blown on one of the sides, the blinkers blink very fast on that side. This is because of how these old breakers work.

If you installed LEDs as turn signal bulbs without resistors - I suggest you put back bulbs and see what happens.

Difficult for me to verify now which one is pin 12 from your description...

MSmith, you have access to the coloured wiring diagrams: https://www.sl113.org/wiki/uploads/Restricted/280sl.jpg
Components descriptions are here: https://www.sl113.org/wiki/Electrical/WiringDiagram

Simplest way to check power for fuel gauge and reserve light:
You have the instrument cluster shown on diagram with all its connections (10a, 10b, 10c....). Fuel gauge is 10d, reserve light 10c, but you should look for the power on the one without a letter (black/blue) as wires from 10c and 10d go to fuel sender in the tank. Brake fluid level is 10i (this one I would skip for now or make sure that power is there only when connectors in the brake fluid cap are closed and both driver and passenger doors are closed). You see the corresponding colours of the wires to all connectors. If you look at the handshake connector (harness side) you can identify which pin is for what based on wire colours. Then you will know if you have power on "letterless" pin for fuel gauge/reserve light power supply pin. This is probably the easiest way I can think of now to determine power supply to fuel gauge and reserve light. If no power there, the other end of this wire is fuse 5.

Simplest way of checking power supply to brake fluid level (that is where I would start, actually):
with ignition on check if you have power on any connector in fluid reservoir cap plug (just pull out the plug with harness wires and check in it), ignition on with the driver and passenger door closed (I know it sounds weird, but there is a reason for that). If not - next step is fuse 5, the other end of this wire.

Simplest way to check power supply for back up and stop lights:
rear lamp bulb holders. Brake light with ignition on, pedal depressed. Back up light with ignition on, reverse gear in. If power is not there, then you would need to move earlier in the path. There are more points there to check, but I would move to the beginning - fuse 5. You will see switches 23 and 24 on the diagram - for later if need be. If power is there and bulbs are not lit - there may be a grounding issue.

To check the fuse 5 wire connection the easiest way is to look up there under dash and check it visually and reaching there with your hand. The wires either hold to fuse No.5 connector or not.

I would strongly advise to disconnect negative battery terminal while getting to the components and put the terminal on without tightening for actual tests only!

[MSmith]

I replaced all of the LEDs in the  dash back to bulbs...everything works as expected.
No problems at all.
Not looking to impedance match bulbs to LEDs and add resistors...or replace bulb by bulb with LEDs and wing it.
I am happy with bulbs, looks great.
Thanks for the help in come up with a solution.
Mark

[mrfatboy]

I replace my instrument lights a couple of years ago with LED.   Instructions are in the tech manual.  I believe there is  a specific bulb that has to be incandescent to supply the resistance.  I forget which one.  Again,  in the tech manual.

Or you can wire your own resistors.