86 SDL, no power to power seats
 

Where do I start? I get nothing on either seat with key on, running, door open and in or out of seat.

I have (part of) an "Electrical Troubleshooting manual " that covers 1986 through 1991. Its missing a bunch of pages in the first part but has diagrams that seem to cover my problem.

I'm confused (no kidding) that the manual shows a relay "H" in the fuse box, but in that location in my fuse box there are two red fuses. However, FYI this is one of the early models that did not have the external fuse 16 update. (but soon will)

I see fuses a, b, 15 and 17 along with a diode and the mystery relay are involved. I have replaced the fuses with no change.

Help if you can and please treat with kid gloves. You are dealing with an electrical ignoramus.

Thanks
Harry

Go into the fuse box and find the power seat relay.

Facing the box from the left side of the vehicle, the fuses are on your left and the relays are on your right.

You'll see four relays in the first row (closest to you).

You'll see three relays in the second row.

Pull the first relay in the second row (closest to the fuses).

Turn the ignition to position 2.

Check for voltage at socket #4.

Report back with results.

Brian, I don't have that relay.

Two things that may not be related, one, I just bought this car back from the guy I sold it to about two years ago. He spent a ton of money on it, but I don't know much of what was done in this area. Two, my manual states that fuse #16 was eliminated as of end number 269896 and my number is 267785. I know this is for the blower motor fuse, but it may indicate I have a different fuse box.

I hope my picture shows.

Thanks
Harry

See the two red fuses that are in the stated location? The FSM shows these fuses sitting above the relay. See if you can remove the fuses and the relay.

The relay that you don't have is to the right of the power seat relay. It's for the air pump clutch on a gasser.

No voltage on pin #4. Middle socket, close to fender. Pins and sockets look clean.

I was not sure what key position is #2, so I tried it in all positions with same results. I verified meter before each test to make sure of a proper ground.

Thanks
Harry

Now, please make the same test with the left front door open and the keyswitch off. If you still get no voltage, repeat the test with the right front door open. If you still get no voltage replace fuse #2, clean the contacts, and make the tests again.

Verify that there is 12V at fuse #2.

No voltage on pin #4 before or after the new #2 fuse cleaned with Diox. 12 volts on each side of #2.

Thanks
Harry

Did you try it with the doors open.........first the driver........then the passenger?

Yes, I should have said that, sorry. I did just as you said and again veified the meter with each read.

Last test:

Verify that you have voltage at fuse #17 and the contacts are clean.

No voltage at #17, both connectors with fuse out, fuse tested good

Turn the key to the #2 position (run) and retest.

I rechecked #17 with the switch in "run" position and had 12 volts through the fuse.

Brian, I think I was doing this at the same time you were telling me to do it.

Go in the fusebox and find the power seat diode.

It's in the third row, directly behind the relay that you just pulled out. It's the smallest thing in the box....about 1/4" wide and 1" long.

Pull this diode out and, hopefully, there will be two contact points beneath it. Take a test wire and jump the contact points.

Turn the key to the run position and verify that the seats now work.

The seats do not work. One diode socket reads 12 volts (furthest from fender) and I verified 12 volts through the jumper. I tried it with the door shut and switch in run. I tried it with switch off and door open, both doors.

I tried it with the relay in and out. Relay socket #4 still had no voltage.

Thanks
Harry

There must be a flaw in the testing procedure............most probably the identification of socket #4.

You have no voltage at socket #4 via two separate circuits..........one though the doors and one through the diode. This result is almost impossible because it would signify breaks in several wires.

One of those diode terminals goes directly to socket #4. If there is voltage at the diode terminal...........there must be voltage at socket #4.

There should be four sockets where the relay plugs into.........numbers 1, 3, 4, and 5.

The four active pins are 2 & 4 near the fender and 1 & 3 on the other side. There is voltage at socket 1 & 2.

There should be voltage at socket 3 and no voltage at socket 1. The relay closes and jumps sockets 3 and 1. If you were to apply battery voltage to socket 1, your seats will work. You might try this and confirm that we've got the correct relay.


Also, look on the bottom of the relay at the pins. Pin 86 should be plugging into socket 4. Confirm this.

I retested. Relay sockets 1 & 2 have 12V all the time, with switch on or off. Sockets 3 & 4 have nothing.

I tried this with the diode jumpered and with the diode installed. There is no volts at the diode with the switch off. With the switch on there are 12V on both diode leads.

There are no numbers on the relay like normal relays. P/N is 1225400950. Pin #1 connects to one fuse and the other end of that fuse feeds 12V to pin #3. pin #2 does the same through the other fuse to pin #4

Happy New Year Brian, its straight up midnight in Newton, MS.

Thanks
Harry

Brian, this relay has no moving parts. Its only a fused jumper between pins 1 & 3 and between 2 & 4 on the other fuse.

The picture is lousy but the holes you see in the bottom are the tops of pins 1 & 3, slap a fuse in and you have the same voltage on both pins.

Something is not right. We need the actual relay for the seats........it's a traditional relay with a coil on two terminals and a load on the other two.

The FSM shows this relay to be directly beneath those two fuses.........??

Is it possible that you are testing the fuse holder and the relay is sitting beneath the fuse holder?

Do either of your SDLs have a relay like mine? Its about 1/4" thick with 1/4" brass fuse connectors rivited to the top of each pin. I tried and failed to locate it at a parts site.

BTW, I mistyped the relay P/N, its 1235400950.

I'm about 60 miles away from them, or I'd check it for you........

Maybe someone else has the vehicle nearby...........

That is not the relay. It's only the fuse holder.

I can see and feel under the case and only the socket base is there. It looks like the socket base for the four relays plugged in next to the fuse holder.

Any 300SDL owners out there that could take a look in the fuse/relay box and see if it looks like mine in this picture? Mine is an 86.

Also, does any one have a good wiring diagram they could pdf? What I have doesn't seem to be for the car I have.

I'll send the picture in my next post, me and the chine are having a fuss.

Thanks
Harry

I'll try for that pic again.

The chine is right again, the fuse/relay box picture is on page one, post # 3

Thanks
Harry

If true, the vehicle doesn't match the FSM.

I'll take a look tomorrow and see what I find on the '86.

I have the diagram in paper so, unfortunately I cannot send it via wire.

Here are some pics of my '86...
it is # 271324

Try this...

Swap the fuse holder and the relay you have in the first row far left position so that your car matches mine.

The clear plastic relay in the middle spot of my pictures is my afterglow set up and should be ignored for this reason.

CA_CHING, every function of both seats work except the head rest on passenger side. That's with the door open without the key and inside with key on and door closed. Even the memory works on drivers side, will check out passenger side later.

Many thanks to LUVMBDiesels and Brian who took my hand and led the way.

I had plans to do some serious digging under the dash and seats, but was waiting for a CD service manual from ebay with hopes it would match the car.

Thanks again
Harry

Awesome!

I am glad to be able to help you like Daw_two helped me...
If you are having issues with part of the seat function do what he told me to do. Pull the button off the switch (they are hard to get off) and spray electrical contact cleaner into the switch while working the stud back and forth. My passenger's seat back, which would not come up from a nearly horizontal position thanks to my daughter, started moving as soon as the spray went into the switch!

We all have to stick together :-)

Brian has been a great help to me and to others in the past...

Regards,

Joe

JUST be CAREFUL pulling those buttons off the post. You do NOT want to break the posts.

Yes use a straight pull backwards, do not wiggle them side to side...

Now that is bizarre.

The FSM drawing is in error. It shows the auxiliary fuse holder in the position for the power seat relay and it shows the power seat relay in the position for the fuse holder.

Maybe the PO was attempting to follow the FSM diagram...........??

Thanks for getting that photo............the snow is too much here to get into the SDL.

Although my role was only the caller on the phone to support, I get a great deal of satisfaction on a fix like this, pumps me up.

I'll try the cleaner on that head rest switch and report back.

Brian, the PO was in the clutches of more than one Indy and I suspect one of them. The records he gave me show two new seat controllers, seat frames and pads. One of the work orders stated "a broken spring damaged a wire and its possible the controller is bad". The list of parts includes a controller.

I know part of this because we became friends as he tried to buy this car from me for two years. I sold it to him two years ago and he dumped a ton of money into repairs including a paint job. The parts list to fix the cruise includes an actuator, switch and amplifier, even I could be that kind of a mechanic.

So I was his PO before he is my PO. I held his check for 30 days in case he decided if was too much of a mess and it was a mess.

It comes back to me with four problems and you guys fixed the worst. Now the blower motor aux fuse kit which should get done today, the driver's window and the radio. Yeah, an Indy R&R the blower assembly. BTW, he even had the outside temp sensor replaced and spent $540 on a new clock and the list goes on, with records, A/C, front end, four Bilstien shocks.

He bought a 94 140 rod bender and fell in love with it. (sigh)

Thanks
Harry

BTTT
 

Ok, I truly hate posting to a thread this old but my 86 560SEL has just developed exactly the same symptoms (no power at all to the front seats under any conditions) after I had completed my annual replacement of fuses/cleaning of relay pins and sockets. :eek:

Having done this numerous times already w/o any problem, I am somewhat suprised to say the least as well as quite reluctant to just drop an "ice cube" relay into place of the twin fuse holder as seemed to have solved the problem for the OP.

Has anyone else developed this problem? While I do know that my diode is on its last legs (soon to be repaired), could a TOTAL failure of power to reach the front seats be the result of complete diode failure?

TIA!

Although its been in moth balls for the past four years, I still have The SDL and if I can help by looking or testing I'll be glad to help. I think you should go back to where Brian started giving me tests to perform and do them on your car. Chances are you'll get fixed quickly. My car had been in the hands of independent mechanics and I'm guessing one may have fouled the fuse box.
Good luck.
Harry

Thank You!
 

Very many thanks for the input and the most kind offer of assistance.

Nothing worse than those journeyman hackers and gnawers, vivisectioners (sic?) of precision machinery, eh?

My Gentleman Practitioner of the Mechanical & Ancillary Arts (tm)* and I will run through those diagnostics just as soon as I have a known good diode in hand because if it isn't that I myself don't have the foggiest idea idea what else it could be given that that "relay" 1235400950 is nothing more than a fuse holder as far as I can see (or understand).

And yet, after having stared at page 130 of the 126.0/.1 Electrical Troubleshooting Manual, it clearly "does" something more than it would appear to me - but what?

Odd.

Anyway, I can't even begin to imagine that putting fresh fuses in and cleaning contacts/connectors with contact cleaner and cotton swabs for the umpteenth time would or (even really could) short anything so if it isn't that "relay" it must be that diode - he wrote with fingers crossed at 4am...

Cheers!

*From Massey Ferguson to Ferrari & Maserati he knows them inside out AND wants to show YOU the how and the why of them all. Sounds like I am lucky to have him and that ya'll down there could really use somebody like him.

RESOLVED
 

Hello all,

In my case it was a complete failure of the diode in part no. 0005404281 that caused the sudden and total loss of power to both front power seats.

Installed in a new unit and seat functionality is back to 100%

So if both of your front power seats just stop working out of the blue w/o any warning or mounting loss of function, your first stop might well be to check out the condition of your Power Seat Diode.

Cheers!