I am trying to determine if the problems are wiring related or component failures.

1- digital clock works intermittently, the fuse that the clock share with ....(don't remember) is fine: problem is failing LCD not electrical ?

2-horn not working , fuse shared with .....(don't remember) is fine: check/adjust contact on ring to horn pad?

3-backup light not working, fuse shared with .....rear wiper is fine, bulbs and sockets are fine: checking ground/ connection under plastic cover by battery, reverse switch?

4- pwr mirror, door lock, dome light not working, fuse #24 is shorted so the diagnostic tool didn't work. I've searched so I'll just have to go through each of these later on as they're on different circuits/ problems. TIA.

 

have you done any cleaning with deoxit applied to the CE panel both front and back?

 

The clock is on Fuse #24 like all the interior lights
There is a horn relay (XI) swap it with another '53 relay, or pull the relay and test terminal 85 on the CE panel there should be continuity to ground when you press the horn button. If these and fuse #18 are good (test the fuse with a DMM - don't look at it - either pull it out & do continuity test OR with it in circuit test for battery voltage in the lower end dimple - look!). if none of those check the horns in the passenger front fender ahead of the wheel (remove: wheel, splash shield & wheel liner.
Fuse #12 (test as before (but w/ ignition on)). There is a relay - another '53 type: (XXII) - Auto cars only. This may be related to Fuse #24 issues also - so fix that first. Assuming "Fuse#24 is shorted" means it blows (not the same thing at all BTW...!) Then you likely have an issues with interior lights. Step 1 remove all the roor/hatch lights and tape up the ends - try replacing Fuse #24. If that works discard any broken light fixtures and reinstall correctly, even functional roof/hatch lights installed wrongly can cause this. See other threads (many) I have posted on how to do these connections correctly.

Alan

 

Hearken to Alan...

Couldn't resist.

 

I checked the CE board for loose contact, corrosion and didn't see any when I had to pull couple fuses and relays. I didn't use Deoxit but will buy and use as additional easy fix.

Thanks Alan for chiming in on these:

1- Clock did come on intermittently so could that run off the 2 small 400mA fuse along with interior light ? I could not find these 2- 400mA fuses to check/ replace. Fuse #24 is SHORTED because it blows the new fuse when I install to test on the diagnostic connector.

2- I'll swap horn relay (XI) '53 another '53 relay, pull the relay and test terminal 85 on the CE panel, and check horn. I searched and most of the horn damage are waterlogged so we'll see.

3-on back up light, I checked all fuses including # 12 with Ohmeter but not with ignition on. I'll swap '53 type: (XXII) relay and see. I'll check to see if this relay is shared with another component. If none of these fix it then I'll wait until fuse #24 is fixed before continue on.

4-Fuse #24 is definitely shorted. I checked all dome light housing and they seem in good condition, no hairline crack, melt. I'll unplug all the dome to check and double check CORRECT connection before plugging back. Arent't these dome light run through the 2- 400mA also? I can't find these 2- 400mA behind the CE panel and couldn't find any pics of what they look like or where they are.

 

Please do not short a fuse w/ a jumper to test, as this is a quick way to destroy your wiring harnesses! !!

Only use correct amp rated fuses as they are there to protect the wires and components.
If you keep blowing fuse, than start disconnecting stuff.

 

Do you mean that the circuit fused by #24 is shorted?

 

Yes my point before was you need to stop saying "the fuse is shorted" - it means something quite different than what you think... if the fuse was shorted it would mean both sides of the fuseholder were connected together without the fuse there - that isn't what you mean - right?

You mean there is a short on the circuit fuse #24 feeds - so just say that.

You are very confused... the 2 x 400mA fuses are inline (on the wire) fuses behind the CE panel and they ONLY feed the door locks - nothing else - leave them alone. The rear wiper relay is on fuse #11 & rear wiper motor feed fuse #18 - The horn fuse supply is shared with the rear wiper motor on #18.

Stop second guessing - read what I wrote, it is exactly true - the interior lights run off fuse #24, don't worry about anything else - just do those tests...

Take out the roof & hatch lights - disconnect. If fuse #24 still blows take out the door lights and disconnect those too.

Alan

BTW you test fuses removed from the panel with an ohmmeter, if they are in circuit you test with a voltmeter on the output (bottom for ATO/ATC fuses - top for the <'1985 GBC torpedo fuses) - but you have to ensure the appropriate circuit is on (some are direct battery supply, some are switched vis accessory or ignition).

 

Problem #1: intermittent clock runs on fuse #24 but fuse is not installed which means it's shorted to a hot wire somewhere. Sorry, I meant circuit for fuse #24 is short, blow fuse 24. I use V-meter to check or a new fuse, never use jumper wire in fuse connection, only in relay test instance.

Sorry, my door lock is not working so I guess that's where I got mix up with the 2-400mA fuse-any pics of what it looks like? I didn't see any fuse or 2 fuse inline on any wire after pulling CE panel to look behind it.

Rear wiper works but horn doesn't and fuse #11 and #18 is fine- checked with ohmmeter. I'll check as Alan instructed and update later.

I am trying to separate component failure vs wiring so I know the common issue. I searched and read a lot and since my car has so many electrical problems but don't remember everything after reading. I tried using Ipad and my BMW diagnostic PC in garage to read the PDF schematic but it's difficult to follow across multiple pages since there are many component running on same fuse or wire. I tried to use the printed paper but it's so small, hard to read, that's why I am trying to tackle 1 small isolate problem at a time.

Thanks to all the responses, especially Alan.

 

Peter I would suggest that you find another savvy 928 owner to assist you in person with these electrical tasks,
from the sounds of your reply's you could be very close to letting the smoke out of your wire harness.

You really need a second set of eyes on this.
By following Alans instructions you should be able to figure out the light this may restore many of the other issues, BUT first a helper should be found to assist you

 

I'd be glad to get some local assistance but not finding anyone yet. I know enough of the basics not to burn the wires or car. While pulling car out of garage, I notice leaking fuel by the pump so went ahead and replace fuel filter and tighten up the crush washer on the pump so that screwed the plan to start checking electricals.

Is there a better WDS than this ? I can barely read some of these so it's hard to trouble shoot. Thanks.

 

please disregard the Wire diagrams for now.

Go to the battery disconnect it.

then remove all of the lights from the roof panels and the hatch,
post pictures of the lamps before you disconnect them and it will be easier to assist you.

The 400ma fuses are on the top of the CE panel clipped into holders behind the top edge,
so they are difficult to see ,
but its usually easy to see the red with black stripe thin wires.

Lets work on the lights first,
also please post a picture of the back of the clock with the wires you have installed,
as it sounds like it may be miswired remove the right side console cover for a good picture.
NOTE also include the lighter wires

 

Here are the pics I got. It's in garage and dark outside so I'll check fuse 24 tomorrow when it's outside.

Top is trunk lid, second is sunroof light.

 

This is back of digital clock. I did not mess with the clock or anything on this area.

Some of the splices, endcaps are from aftermarket stereo that I plan to remove later

 

Mod, please delete this. Thx.