gergstuff

Hello!

I just aquire a 78 928 yesterday in a trade.

It only has 57000 miles on it and runs well.

It is however beset by electrical gremlins.

Several dash warning lights are blinking and the voltmeter gauge works intermitantly. Sometimes it shows that it is charging and sometimes not.

I just found this site so I will search the forums and helpful guides if any before I start asking questions.

Any helpful general advice?

Thanks,

Craig

The Forgotten On

Read the new member sticky at the top of the list of threads.

It will have links to all sorts of helpful threads and should help you with many things you want answered as I am sure some one has faced those issues before.

82Porsche928

Best place to start is with all the grounds. There's a few treads here with locations of them all. Completely clean them. Make sure all relay tabs and fuse tabs are clean in fuse panel (pink eraser, and follow up with deoxit) once that is sorted out you will know what else needs attention, and will get better readings when troubleshooting. Also, check the FAQ at top of page as it is very helpful. Best way to search this forum is with Google, not the forum search. Everyone here is very friendly, and helpful! Post pics for us to see, and your year, and specs in signature line to help with future posts!
Best

Landseer

Welcome Craig. Congratulations on the low mileage 78. Should be fun. Begin by cleaning the ground points, 14 pin connector in engine bay, and clean / new fuses for fuse panel under passenger side feet cover.

You might enjoy reading some of the links below.

https://rennlist.com/forums/928-foru...s-car-1rc.html

WallyP

Sometimes it seems as if the 928 is susceptible to a lot of electrical problems. You can forestall many of these problems by doing preventative maintenance on the electrical system. While I refer to it as "annual" maintenance, once every five years will probably take care of most problems.

1) Open the hatch and remove the tool panel. Remove the carpet and spare tire cover. Remove the spare, tools, etc. Open the battery box.
2) Disconnect the ground cable from the chassis. Remove the negative battery terminal connector. Remove the positive battery terminal connector. Remove the battery hold-down. This is a curved piece of sheet metal, held by one bolt. One end holds down the lip at the bottom of the battery. Remove the battery. Use extreme caution to avoid getting battery acid or residue from the top of the battery or cables in your eyes. Goggles are recommended. If the battery brushes against your clothes, you can end up with holes.
3) Clean the battery terminals until they are bright and shiny. Dull gray won't do. If it is possible to check the fluid level in the battery, do so. Fill to the rings. Wash the battery. Put it on a charger if possible.
4) Clean the battery box, removing all corrosion. Wash the battery box - baking soda neutralizes the battery acid. After it dries, touch up the finish as required.
5) Clean the battery cable terminals (all three) until the connection area is clean and shiny. Dull gray or rust won't do. Clean the connection area on the chassis. Carefully check and clean any other connections on the positive battery terminal. On later cars, these are very critical power supplies for injectors, fans, etc. Inspect the flex ground cable very carefully - they have a habit of wicking battery acid into the flex cable and corroding, which causes hard-to-find problems.
6) Clean the electrical connector in the right forward corner of the spare tire well. Depending upon the model year and transmission, this connects speedometer drive, neutral start switch, gear indicator lights, etc., etc. This is an important connector.
7) Raise the hood (bonnet). On the right fender panel, find the jump start terminal. Remove the protective cap from the jump start terminal and pull the protective plastic cover from the terminal. If you are missing the cover or the cap, replace them - they are critical items. If there is no cover, water will enter the connector and corrode the connectors and wires, causing serious electrical problems. There should also be a short piece of plastic trim clipped to the edge of the fender flange just above the terminal to divert wash water and rain water from the connections. If the connections are clean and tight, replace the cover and cap. If the connections show any trace of corrosion or any looseness, disassemble, clean and reassemble. Much of the electrical power for the car flows thru these terminal connections.
8) Find the fourteen-terminal connector near the jump start terminal. This is a common trouble spot. While I suggest that you disassemble and clean these connections, be aware that the wires can and will fly in all directions if you are not very careful. I would suggest digital photos before and during disassembly! Clean all of the connections, and check for corrosion running up inside the wire insulation. Reassemble the connector. (In an emergency, you can jump power from the jump start terminal to the yellow wire in the corner of the connector to operate the starter. Be aware that the starter will operate with the car in gear, and the car will run over your foot.)
9) Jack the right front of the car and support it so that you can SAFELY work underneath.
10) Remove the ground cable that runs from the right side of the engine to the chassis. Clean both ends of the cable, and check for corrosion in the cable. Clean the connection points, and reinstall the cable.
11) Check the heavy cable connection on the starter solenoid for damage, looseness or corrosion.
12) Check the moderately heavy wires on the same connection for corrosion and breaks inside the insulation. These carry the charging current from the alternator and from this point to the jump start terminal.
13) Check the small yellow (may look brown, cream, etc.) wire connection for corrosion and tightness. This wire triggers the starter solenoid.
14) Lower the car. Do some research online or in your wiring diagrams and find a diagram showing all of the grounding/earthing points on the car. These are shown on diagrams by "MP" (Masse Point) and a Roman numeral such as "MP IV". Carefully clean each of these. Do more research if you can't find them - the harder they are to find, the more critical they are.
15) Fold back the carpet and open the central power panel cover. Check the main power connections at the top of the panel for tightness and corrosion.
16) Check the ground connections above the panel for tightness and corrosion.
17) If you do not have a diagram of the fuses and relays, go to the Tips section of our web site and print the correct chart for your car. If you have round fuses, carefully clean the fuse clips, and make sure that the fuses fit tightly. If you have the newer plastic fuses, remove each in turn and make sure that the fuse connectors fit tightly in the connectors. Check each fuse for the proper value, and examine them visually for damage or corrosion. Any trace of overheating of the fuse or its connector is a definite indication of a bad connection, and must be corrected. NEVER use cheap fuses! Cheap imported fuses have failed to blow under overload conditions, causing damage and fires. While you can test fuses with an Ohmmeter, it is easier to test them with power applied. Later cars have a fuse tester built into one of the relays. You can touch the tiny metal bits on the face of the plastic fuses with one probe of a voltmeter/multimeter (other probe grounded) - you should have power on both bits or on neither bit, depending upon whether the circuit is powered. You can do the same test on the older round fuses by touching each end in turn with the ungrounded probe. Again, both ends or neither end should have power.
18) If you feel that it is necessary, remove and reinsert each relay. This won't be easy, as they fit very tightly in some cases. Porsche sells a relay removal tool, but I am not impressed. It is basically a pair of pliers with square jaws, and will pull the relay apart. One tool that works well is a paint can opener, usually available free at a paint store. This is a small tool made of bent steel wire, with a loop on one end and the other end having the last 1/8" bent over at a right angle. You can put this angle under alternate bottom edges of the relay and lift it out - IF the battery is disconnected!
19) Close the panel and replace the carpet.
20) Replace the battery and install the hold-down. Install the positive cable. Install the negative cable. Put a drop of oil on each nut. Connect the chassis end of the ground (negative) cable. Lubricate the battery box latch and close the box.
21) Lubricate the wiper drive shaft and hatch latch mechanism.
22) Clean the spare tire, jack and tools. Put a couple of large heavy plastic garbage bags in the spare tire well for emergencies, along with a tube of hand cleaner and some paper towels. Nitrile gloves are really nice to have. Install the cover and carpet.
23) Lubricate the jack, and put it inside the tool panel. Clean and lubricate the tools. Reinstall the tool and tool panel.
24) Reset the clock and radio presets.

gergstuff

Wow! Seems like I've got some work to do! I have started reading through all the previous posts under helpful hints and the above laundry list too. Thank you! Fortunately I have a 2 post lift so it makes life a lot simpler and safer that jack stands. Have not taken any photos yet but will post some when I can. So far I have just vacuumed out the inside, found .65 cents and some tools-added bonus!

M. Requin

Mods, Wally's post should be added to the New Visitor's FAC, I think. Excellent.

crushingday

^ what he said. Also we need to see pictures of your car. Folks around here don't take kindly to not having pictures Welcome!

James Bailey

The first and only time you will get money back from your car as long as you own it... good luck with the adventure. The front engine wiring harnesses get pretty rotten over time and the plastic foil circuit board on the back of the instrument cluster often fails or has the tabs broken where the harness connects under the pod.

Fogey1

+2

autoslave

I would check both sides of any/ every circuit in the fuse panel. With the car ON there should be power on both sides of nearly every fuse.The copper spring loaded terminals can corrode especially when non-copper fuses are used in the panel. Clean the bad ones, and heck clean all of them.
This is probably the simplest thing to check then it's on to the grounds described in the earlier post.
Good luck and welcome too.

christiandk

Warning lights - socket on relay under dead pedal drivers side.

Pics!