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common electrical issues?

Hi folks,

I had a customer drop off his '84 928s today at the shop to look into some electrical issues the car is having at the moment. I rarely see 928's here, mostly 911's and 944/968', so I'm not that adept with their specific electrical gremlins.

Typically when driving the vehicle down a bumpy/rough back road the warning lights in the cluster will illuminate for no reason. Sometimes one at a time, more often all at once, then just as quickly they'll go out. Car has had zero running or performance issues otherwise when this happens

I place this as being a faulty ground as with alot of these older Porsches, but am not sure exactly which one. Is this a common issue with this chassis? Is there a specific ground or cluster of grounds I should be looking into(location)? I have yet to really tear into the vehicle, and it's one of those that while a good runner, it's not worth it to the customer to have me spend 20 hours in labor diagnosing the electrical system when he only paid a few thousand for the car itself.

Thoughts or ideas?
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Old 10-22-2010, 09:43 AM
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Tell him I will offer him $500 to take his electrical gremlin off his hands

Seriously, there is a chart out there that will show every ground point that normally get's corroded with age. There are a few ground points on our car's.
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Old 10-22-2010, 10:43 AM
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Here is an S4 diagram but probably similar locations

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Old 10-22-2010, 10:44 AM
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There are seven main ground points shown in the workshop manual;

battery ground strap
two clusters of grounds above the central electric board (passenger footwell)
engine ground (passenger side underneath car)
ground on front left crossmember (near headlight drive tube)
ground on front right crossmember (also near headlight drive tube)
ground under instrument panel/steering column
ground in right rear corner of trunk, under trim panel

does it only happen on bumpy roads?

WSM states that the central warning computer is supplied voltage via a specific terminal when starting the engine which cancels the bulb check function. A faulty alternator can cause the warning lights to flash all at once. If some flash individually then it could be loose/corroded connections for those particular circuits as well.
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Old 10-22-2010, 05:11 PM
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since your not familiar a few pointers
The battery is in the rear of the car under the spare tire in a box.

The most common failure point is a corroded ground strap from the neg terminal of the battery to the chassis,
the strap can fail at the chassis ground,
clean this connection with an eraser, do both sides of the ground strap also look at the strap itself see if the webbing is corroded inside the plastic sheathing, if so then replace the ground strap.
Also clean the battery terminals both pos and neg take all of the connections apart and clean them .
There is a big ground strap from the right side of the Block to the chassis just under the # 3 exhaust port. Clean this on both sides.
NOTE the 928 Firing order is 1 to 4 on front right,
5 through 8 on the left front as viewed from the drivers seat.

Next is a connection called a hot post, this is on the right fender well next to the front of the timing belt cover, As it states it is hot all the time the battery is connected there should be a cap that covers the 11mm stud and a black cover that goes over the wires, (if there isnt one then get a hot post cover from a 1988 S4 )
remove the hot post stud cover and the black cover you will see an 11mm stud holding 3 thicker wires ..
(these come from the alternator and go to the CE or central electric panel this CE panel is just under the glovebox , remove the footwell carpets and lift the wooden cover to get to it.)
Unscrew the 11mm stud with the battery disconnected and clean the ends of these wires with the eraser.

Also just above the hot post stud is a 14 pin connector this connector also has power flowing when the battery is connected (Hence the need for the black hot post cover) this connector is prone to getting wet if the cover is not installed this will cause corrosion on the pins clean them with the eraser.
refit all of the connections pay attention to the thicker red wire thats connected to the hot post this wire can sometimes shed its insulation its a good idea to put a piece of heatshrink on it prior to refitting it since its carrying positive 12v all the time.
Next go to the CE panel there are 2 bolts above the panel they hold about 12 brown wires these are grounds for various systems, just above the CE panel is the bottom of the blower box, see the grate.
This blower box is also prone to leaking water onto the CE panel from its edge seal , this will be evidenced by seeing rusty bolt threads and white drip trails down the CE panel supports, if you see this then its a good chance the Blower box needs to come out for a reseal of the strip caulk.

Anyway clean the brown wire ground connections above the CE panel.

Also on top- of the center of the CE panel is a clear cover, this covers about 3 or 4 red wires this is the power supply to the CE panel from the hot post, clean these connectors as well.

Get a fuse relay chart here 928gt.com on page 2 under tips and links print off a copy.
The Fuses are numbered from 1 to 45 or possibly less on the older cars starting from the left side of the panel as you look at it.
Remove each fuse on the Ce panel and clean the ends of the fuses and the fuse holders, with the eraser.
Make sure that the correct fuse is in the correct slot, also make sure that any empty slots are in fact empty.

Next do the relays, there are specific relays for the various systems, some are common called # 53 relays .
Anyway remove the relays ans note the positions, there are Roman numerals on the CE panel with small arrows that point to the respective positions. Make sure the correct relay is in the correct slot, also make sure that the empty slots are in fact empty.
there should be a few slots that dont have any relay in them.
Clean the relay pins with the eraser, any relay with corroded pins should be smelled for burning and opened and the internals inspected, water dripping onto the CE panel will cause this damage.
. Make4 sure to verify the correct relay is in fact in the correct position , there may be a relay with a fuse tester on its top this is a #53 relay, so it can be installed in a #53 position.

Moving on check the starter connections make sure the wires are tight and the wires are not touching the sway bar,
the sway bar will wear through the harness as it moves when the car is in motion.
Next check the alternator, this may require dropping it to remove the back cover, leave the alternator hanging with a piece of mechanics wire while you work on it,

Caution the alternator harness has a a thick red wire and one thin blue wire running in the silicone sheathing ,the thin wire can shear off just outside the black cover if you let the alternator hang from its harness so use mechanics wire to hold it with slack in the harness.
After removing the rear cover remove the regulator check the brushes for wear if they are short then either replace the brushes or replace the regulator only use Bosch parts for a new regulator as the off brands will not provide the best service life .
Most alternator issues are due to failed brushes or a sheared blue wire, (the blue wire runs through the 14 pin connector above the hot post)
Refit the alternator back cover being careful with the harness so its not pinched, then fit it to the engine, make sure the air duct tube is also refitted as this tube has a temp sensor in it , the alternator fan pulls air past to let the sensor compare outside air to inside air.

NOTE most of the elex issues should be corrected if you have done all of the previous instructions.

The warning light boxes are under the dead pedal one black and one yellow connector they dont usually cause problems.

If your still having issues then

Next is to remove the gauges/ pod and clean the slip on connectors there are 3 of them use the eraser so the foil tins are clean ,
please report back prior to pod removal for further instructions
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Old 10-22-2010, 07:37 PM
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928: Serial Enabler
 
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Some great information above. I need to subscribe to the thread!


Regarding grounds for 1984: The engine electronics are grounded to the passenger side cam cover. That wasn't mentioned yet.


Regarding Warning Light flash. This happened to me today. I don't know why yet. I got an occasional downward blip of Amp gauge. Also, an ocassional few flashes of warning lights. Happened with significant throttle / load. Am wondering if its an intermittent alternator failure or a failing brake fluid level sensor. Don't know. Still running strong. Coincidence with your customer's issue.

On 84 thru 86 the warning lights are triggered by loss of alternator as battery power fades. They will all flash repeatedly until battery finally depletes and car dies. Its a wiring change that was made after 83. I've had an intermittent failing alternator cause this. Slight hammer tap would settle the alternator, but it would repeat after a week or so. Replacing alternator with factory rebuilt Bosch which completely solved situation on 86. But this situation today with my 84 seemed different. Battery was still very strong, got the amp meter blip, then a couple flashes, then recovery. Sorry, no definitive answer. Might also be some sort of short, as this 84 electrical system has suffered abuse.




Had some other various pictures to reinforce other posts:

Here's an 84 fuse panel.
See the site mentioned for ref.



Here's the back of it. Melted wires can happen.



These are the hot leads on the 84 panel, they aren't under a clear cover (minor difference from notes above)




I always replace all these, plus clean the heck out of them. Like Stan says, they corrode because of moisture from above.


Last edited by Landseer; 10-22-2010 at 10:56 PM..
Old 10-22-2010, 10:39 PM
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928: Serial Enabler
 
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Am using 53 relays in place of any labeled 53 or 24, BTW.

I've also had gauge blipping caused by intermittent contact / broken wires in 14 pin connector (mentioned above).

Here's the map of the wires. One of the surfaces of the unit has terminal numbers:




Here's 14 pin and hot post mentioned by Stan:









Hope something here helps you ( and me ) solve this flashing problem.

The car I'm having trouble with was the first car I worked on. It didn't get a good 14 pin cleaning 3 years ago, so I'm starting there.

Last edited by Landseer; 10-22-2010 at 10:54 PM..
Old 10-22-2010, 10:50 PM
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Here's another reference to early car ground points (ABS was optional for 84):




Old 10-23-2010, 12:07 AM
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I had a similar issue with all of the warning lights coming on while driving down the road, turn out to be an ignition switch going bad.
I am not an expert, but I bet this one is the main ground strap, or a positive wire, alternator, or the ignition switch cutting out momentarily.
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Old 10-25-2010, 04:33 AM
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Could be!
Mine is new ( make that 2 years old, time flies ).
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Old 10-25-2010, 05:20 AM
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Old 10-25-2010, 05:20 AM
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