560SL electrical fault - PeachParts Mercedes-Benz Forum

rjk · #1 01-06-2009, 11:00 PM

Hi all,

'89 560 SL
fine yesterday.
today have lost some electrical (dash gauges, windows, directionals).
I DO have headlights (hi & low), radio, int. lights, emerg. flashers, dash lights, engine works so I assume engine management is live as well.
checked fuses, they are all good.
checked voltage and many fuses have no voltage present on either side including fuse #13.
I checked under the hood and there is voltage present at the large gauge wires on the passenger side.
so, where do I start?
I want to be able to start a focused search and avoid wasting a lot of time running down blind alleys so any help would be appreciated.

rjk · #2 01-07-2009, 02:10 PM

Sorry guys, I have no idea what I did to "Close" the thread but it is open now.

My basic need here is to see if anyone has had a similar problem and where they found the cause.

Which fuses are on the same bus as #13 which seems to be the problem ckt?

Which wire feeds fuse #13?

Can I access anything without pulling the fuse block or is that where I need to start?

Deltacom · #3 01-07-2009, 03:13 PM

Quote:

Originally Posted by rjk

Sorry guys, I have no idea what I did to "Close" the thread but it is open now.

My basic need here is to see if anyone has had a similar problem and where they found the cause.

Which fuses are on the same bus as #13 which seems to be the problem ckt?

Which wire feeds fuse #13?

Can I access anything without pulling the fuse block or is that where I need to start?

Suggest checking OVP relay. Following circuits are fed by the specified fuse. Hope it helps.

rjk · #4 01-10-2009, 12:34 PM

OK, I have the pass. dash/kick panel disassembled and have a few questions.
Which is the OVP relay?
Is it the tall relay with the attached 10A fuse?
(Fuse is OK, I will disassemble relay to check inside)

Is there a layout diagram somewhere?
(I see many relays, 5 over the fusebox and 2-3 more above the A/C unit)

It looks like I have a dead ckt, 58R.
Voltage is NOT present at fuses #9 or 13 but I see #9 has no identifier so I assume it is a spare.

I did find the fault affecting the pwr. windows so that is now good.

Is there an online downloadable wiring diagram somewhere I can purchase?

rjk · #5 01-10-2009, 01:27 PM

I disassembled the unit I think is the OVP relay (tall w/10A fuse on top, has #126 5404745 stamped on the outside).
There is a power diode inside that shows NO continuity in either direction with my multimeter.
Assuming the meter passes enough current or has enough voltage to overcome the threshold voltage of the diode, I think I found my culprit.
Anyone in disagreement?

Would there be any danger in jumping the diode until I found a replacement?

dugald · #6 01-10-2009, 04:21 PM

rjk
I sent you an email

rjk · #7 01-10-2009, 06:53 PM

All fixed!
Fuse #3 was bad, hairline crack in the element, not noticable to the naked eye but showed up when one side showed hot voltage and the other side zilch.

OVP was weird, is it fed by fuse #3? I cleaned the contacts and everything works as it should now.

Thanks for the help. It pointed me in the right direction.