924/944/968 Frequently Asked Questions

13.0 Electrical

13.1 My engine suddenly stopped running

Electrical problems may be the reason why your engine suddenly stops running, either permanently or or intermittently. The first possible culprit is the DME relay. This relay controls power to the DME (the engine management computer) and to the fuel pump. With age and vibration, the solder on the relay's internal circuit board can crystalize and develop fractures. These fractures cause open circuits within the relay, and it stops working.

A spare DME relay in your glovebox is an excellent insurance policy. If your 944 ever suddenly stops running, try swapping in the new relay.

If you have ruled out the DME relay, the next common electrical culprit is the factory alarm control unit (ACU). The ACU is located in the passenger footwell and is about the size of a pack of cigarettes. To disable the alarm on 1985/2-1988 cars:

On early 944 cars as well as 924S cars, the colors of the wires are different. The 15/87 wires are black and green; The 61/61 wires are blue and blue/white.

On 89 and newer cars with the 928 alarm box, jumper 15 (pin 1) to 87a (pin 3) and the car will start and run.

13.2 My antenna on my early 944 (the garden variety non-windshield antenna) is broken. Where can I get a replacement and how do I replace it?

The original Porsche part is approximately $300 and can be ordered from many mail order places. If you're not worried about originality, there are several non-Porsche power antennas that will work in the $80 range. They don't fit exactly, but they do perform the antenna function.

To replace the antenna you need to remove the charcoal canister in the driver side fender and unattach the hoses that connect to it. After getting the charcoal canister out of the way, you can now see the antenna motor. The bottom of the motor is held in place by a nut and washer, the top is held by a nut outside the car on top of the antenna. Carefully remove the nut and the entire assembly will come free.

13.3 My AM radio reception is terrible, but FM seems to work fine, what’s up?

Poor AM radio reception is typically caused by the pre-amp not receiving power. Apparently the pre-amp is not required for good FM reception if they have fairly strong signals. The power to the pre-amp is sent through a black wire in the same sleeve as the power antenna. +12 volts should be applied to this wire whenever the radio is on. Most radios have a "Power Antenna" wire that should work for this function. Directly connecting +12V would be a bad idea since it would eventually drain your battery.

13.4 How do you remove the stock Blaupunkt radio?

As a security measure, the Blaupunkt radios are mounted in a special bracket with no obvious means of removal. There are 4 holes at each corner of the radio face that are used to unlatch the radio. Although there is a special "tool" available to remove the radio, the simplest way to use 4 pieces of stiff wire or nails. Simply insert them into the holes and the radio will come free.

For the 924, the radio pops out with less trouble. The two spring brackets on either side are easily persuaded out with a hooked piece of wire.

13.5 Ignition wires are HOW MUCH!? What's so special about Porsche wire?

Nothing. Wire is wire. After a few years, the insulation breaks down and you get a pretty light show under your hood from arcing (obviously, this is pretty bad for your ignition system). Also connectors can fail, leading to poor ignition.

When one ignition wire or connector fails, others are likely to soon follow. Replacing each wire or connector one at a time is possible, but it might be false economy, particularly considering the time to diagnose the flaky wire or connector that is causing a cylinder to miss. Even then, you are left with a set of old cables dangling on the new connectors not to mention more money and time spent.

It is possible to replace the actual cable while retaining the connectors. Normal ignition wiring will work fine. To repair the wiring, unscrew each wire that has a threaded end. You can remove the old wiring by picking it out after cutting it near the connector. After the connector is free from the old wiring, you can drill a small hole into the base. Cut some bulk ignition wire to the proper length, strip off just enough insulation to properly seat in the connector, and solder them together. Follow the same procedure for the other end, rethread and tighten (you may want to add some dielectric lubricant on the wire and cup, both Jim Pasha & Bruce Anderson recommend this stuff for any electrical work. Porsche's factory response is that it's a no-no because it may gunk up and cause a poor connection.) It is possible that you will destroy the connector in the process of rebuilding it, so you may want to pick up a spare or two from a junkyard or dismantler.

13.6 Can I upgrade my headlights to something brighter?

One of the best lighting upgrade appears to be the Hella H-4's, sold for off-road use only, of course. These are halogen based and come with 55/60 watt bulbs. Brighter replacement bulbs are available. Be aware that in the U.S. you may be hassled by the police if you continuously drive around with 100 watt laser beams of death. Hella lighting is available from most mail order houses. Figure around $80-120 for the headlights, plus $15-30 each if you want upgraded replacement bulbs.

The replacement bulbs include:

If you upgrade to higher wattage headlights, you should consider installing a relay near the headlight. The reason is that the higher wattage draws more current. This can stress the original headlight wiring and switch and ultimately cause some failures. In addition because the factory wiring wasn’t designed for the higher current, it will introduce some voltage drop. This can lead to less bright lights, but worse because of the sensitivity of halogen bulb life to voltage, your bulbs will probably not last long enough. Halogens need the right voltage to work properly.

13.7 Where are good locations to install stereo equipment?

Amps

Under glove box.

CD Changer

Left or right rear storage compartments. The smaller six disk changers fit here nicely. Make sure the changer you buy will work on its side/any angle to avoid mounting problems.

Since this subject is large enough to fill up the FAQ by itself, take a look at the car audio information at The Stereo FAQ.

13.8 How do I reset the air bag indicator in my dashboard?

The following applies to 1988-forward 944-series cars equipped with air bags. It does not apply to the 968. The 968 air bag light can only be reset using the Bosch "Hammer" diagnostic tool.

On the passenger side foot well, at the top under the dash, is a white "Molex" connector that goes nowhere. It has three pins in it, and the center one is the test pin. If you look at the end it will look like the following figure, with three holes in it. Inside each hole is a metal contact:

Pin # 2 is where you must connect a wire and run it to the drivers seat. Connect a ground lead (for example, the metal door latch on the passenger door) from ground and run it to the drivers seat. You will do a series of connections and disconnection to the two ends of the wires to perform the Air Bag reset procedure, so go ahead and take a seat in the drivers seat and have your keys ready. Oh, you will need a watch with a second hand to count time. Remember that this is a German car so be punctual about your timing.

Procedure:

  1. Engine off - key in off position.
  2. Connect both wires - grounding the test pin.
  3. Ignition switch on (run position) do not start car.
  4. After 5 seconds disconnect wires.
  5. Wait 5 more seconds.
  6. Reconnect wires, grounding test pin again.
  7. After 5 seconds disconnect wires again.
  8. Wait another 5 seconds!
  9. Turn off ignition.

Remove the test wire and try starting the car. If all went well you should see that air bag warning lamp extinguish in about 10 seconds (the longest 10 seconds in you life!). If that fails, try again. If it fails after the third attempt you will need to use a different procedure to "READ" the fault code to find out why the unit is faulted. That procedure is similar, but the fault codes are encoded and you will have to get them from the air bag service manual (WKD.493.621).

13.9 Aside from chips, is there any adjustment I can make to my car's DME?

There is a provision on the Motronic cars (944 and 911) to make small adjustments to the fuel mixture (injection pulsewidth) and the ignition timing in order to compensate for the quality of fuel available in your particular country or region.

There is an board-mounted eight-position rotary switch accessed through the little hole in the back side of the DME box. These adjustments can be made without opening the cover of the DME box, unless you have a California vehicle, which will probably have a metal plug over the hole instead of a plastic fitting. The switch has a triangular-shaped recess in which to insert a special adjustment tool — I just whittle down a golf tee to make mine.

The switch has detent positions so you can count the clicks to tell where you are set. All the DME boxes I’ve ever seen have been set on position #1, so I call that the stock position.  Position 1 is fully counterclockwise, position 2 is the next position turning clockwise. The adjustments can be found in the following table:

switch position fuel mixture adjustment ignition timing adjustment
stock 0 0
2 +3% 0
3 +6% 0
4 -3% 0
5 0 -3 degrees
6 +3% -3 degrees
7 +6% -3 degrees
8 -3% -3 degrees

This information is from a Bosch service center bulletin that was distributed by Porsche. The figures are not exact due to the fact that the timing delay is done on silicon rather than being an actual timing calculation. The variance between will cover the figures quoted. The advance or retard adjustment for each switch is thus pretty correct.

13.10 Where are my Fuses?

The Series 1 (82 - 85) cars have their fuses divided between two old-style fuse boxes in the car whose design will be familiar to owners of VW's from that period. With the Series 2 cars, starting in mid-'85, Porsche modernized the electrical system to a Central Electric Box design which located the relays and fuses in one modularized system that was reliable, easy to get to, and easy to customize.

The following information is for the Series 1 cars, for model year (MY) 84 and 85. We do not at the moment have documentation for the earlier cars. The main fuse box fuse layout is as follows:

Relays

position use
1 Fan
2 Fuel pump
3 Blower
4 Headlight cleaners *
5 Warning time relay with gong (USA)
Catalytic converter monitoring unit (Japan)
6 Rear window defogger and seat belts
7 Plug bridge (terminals 56 - 56b)
8 Additional high beams
9 Horns
10 Intermittant action
11 Flashing lights

* - Relays 4 and 5 changed since December 1984.

Fuses

position use amperes
1 Low beam, left 8
2 Low beam, right 8
3 High beam, left 8
4 High beam, right 8
5 Additional high beams 16
6 Hazard lights 8
7 Radio, clock, cigarette lighter, inside lights 8
8 Stop lights 8
9 Backup lights, turn signal indicator lamps,
outside mirror motor
8
10 Outside mirror heating, control wire for rear
window defogger
16
11 Windshield wipers 8
12 Instrument light, glove box light, ashtray light,
license plate lights
8
13 Marker light, right 8
14 Marker light, left 8
15 Front fog lamps 8

The fuses in the auxiliary fuse box are as follows:

position use amperes
1 Concealed headlight motor 16
2 Fuel pump 16
3 Blower motor 16
4 Rear window defogger 25
5 Condensor fan (air conditioner) 16
6 Compressor, evaporator fan 25
7 Rear fog light 8
8 Power windows 16
9 Blower, tailgate unlocking motor 16

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