Chapter 11 - Electrics

1 - Alternator

2 - Headlight motor

3 - Speedometer

4 - Relay and Fuse ID/Locations

5 - Heater/AC Blower Fan Upgrade

6 - Dim dash light repair

7 - Rear defrost repair

8 - Fuel Level Sender Cleaning

Ignition electrical components covered in the Ignition Section.

Before tackling a major or minor electrical problem, or, more to the point, throwing up your hands in despair and walking away, read this How-To on electrical diagnosis and repair.


1 - Alternator Bracket Modification Upgrade

Canadian Spec 924

The Maple Leafs Mod.

Oh, and may I give something back?  Have any of your readers or friends with 924's noticed that the bracket that holds on the alternator breaks right near the engine block, bends or is otherwise inadequate?  Well, mine broke a number of times.  The previous owner had replaced it no less than three times.  And this was after the alignment of the belts and belt tensions were torqued to spec.  Here is a nifty solution that has solved the problem of the 'mischievous' alternator bracket.  Remove all power sources.  Take a hockey puck, preferably a Toronto Maple Leafs or New York Rangers puck. Drill a 3/4" hole in the center of the puck to a 1/2" depth.  Place a bolt with washer through the puck and mount the remainder of the bracket, the part with the sliding apparatus, to the puck with a nut.  Mount the puck against the engine block and slide the apparatus until it the desired belt tension is reached, and tighten the nut and bolt on the sliding apparatus. Re-ground the alternator.  The alternator now cannot move as it is held firmly against the engine block.  Reconnect the power sources.  No kidding - it has not failed yet and I get full charge.  Even Porsche mechanics think it is cool.

Shameless Plug: Oh, by the way, my partner and I have a business wherein we make custom tailored leather seat covers for the Porsche, Saab, Mercedes, Volkswagen, Ferrari, etc.  The leather is of the highest quality, it withstands perspiration, acetate, and most any moisture, it is triple stitched, lined, and embossed to specifications.  It is the best hand work money can buy.  It can be removed and cleaned when required with the removal of a few snaps.  All colors. Usually a little over $1000 CDN.  If you know anyone needing some custom work, please let them write me at

Thanks. Richard.

Using a Delco Alternator on the 931
I have seen a few posts about using a Delco Alternator on the 924, and thought I would share my experience with using one on my 1980 931. I switched to the Delco about 1989 and have had no problems whatsoever since. To make the switch, I just removed the old aluminum lower bracket from the block and fashioned one of similar shape to fit the Delco from a piece of flatiron that I bought at Home Depot. I drilled the bracket to match the two original bolt holes, and used the original bolts. I did not use any rubber donuts. For the upper bracket, I bought a chrome universal alternator bracket from JC Whitney. It is shaped somewhat like a banana. To make it work, you need to cut it with a hacksaw and either weld it or bolt it back together at a slightly different angle than original. I just overlapped the two halves and drilled and bolted it back together, to get the angle I wanted. Once again, I used the original mounting bolts. The alternator I used fits a 1986 Camaro, 2.8 V6, with air. I bought it at a local Checker auto parts for $49.95, and it has a lifetime warranty. You will also need the plug for the alternator. It is available at most auto parts stores for a couple of dollars. Wire the red wire from the plug to the battery connection on the alternator (with the original battery connection). Splice the brown wire on the plug to the blue wire that went to your old alternator. Leave the Delco pulley intact, and use your original alternator belt. Works fine, lasts a long time. I have pictures if someone will tell me how to post them. Thanks, Dave.

2 - Headlight Raising Mechanism

The headlight raising motor and mechanism are very reliable on these cars, due to a simple linkage design, and the use of only one sturdy motor. The
same layout is used on the 924 and 944, but the 931 had the headlight motor on the left-hand side of the car, instead of the right, to allow room for
the air flow meter. Otherwise, the systems are identical. Notes in this section about working on the headlight linkage motor can mostly be applied
to the windshield wiper motor; though the internal components are different and not interchangeable, the design is very similar.

The relay for the operation of the motor is plugged into the side of the motor housing itself, right next to the connector; these both can be found
by pulling back the rubber boot on the side of the motor opposite the linkage. They can go bad, as any other relay, but are easy and cheap to

Be sure to keep all rubber boots and seals intact on the motor and connectors - they contribute greatly to the reliability and longevity of the

One possible cause for failure or trouble is the body of the car interfering with the headlight motion; switch the headlights on and off, watching the travel and looking for any sticking. In particular, if the headlight motor will not operate, the linkage can be disconnected from the motor and moved manually. This sticking can be caused by body damage or by misalignment of the headlight buckets. The alignment of the headlight buckets can be changed by loosening the three bolts in each pivot mounting plate on each side of the headlight. The inboard bolts are easy to see just over the radiator; the outboard bolts are reached from the inside of the fender. Body damage may require some manipulation of the sheetmetal to fix.

The electrical connection can be another source of malfunction. Sometimes the pins in the 4-pin connector themselves can get worn, and not provide a good connection. This can be verified if, when the lights are turned off or on, and the motor will not lower or raise, wiggling the connector will cause the motor to move to the correct position. In this case, the pins can be either made to fit more snugly with a pair of pliers, or replaced outright; the connector type used here is a standard AMP connector type, and the pins and sockets can be removed from the connector block with a special tool for this purpose, which can be purchased at any Radio Shack or other electronics supply house. They will also sell replacement pins or sockets to be crimped on.

Usually the failure is in the female side, on the motor. In order to get at the motor side of the connector, the lower rubber boot must first be pried off of the motor; remove the motor from the car by unbolting the linkage and unbolting the motor, then use screwdrivers or similar to pry the cover off. Prying the rubber boot off can be made easier by unscrewing the two flat-head screws that hold the connector/relay to the motor; the rubber boot will pry off more easily once this is done.

Once the cover is off, the whole connector can be seen. The pins are easy to replace at this point. However, often the female pins need simply to be tightened up. There is a small tab in the end where the male connector is inserted which can be gently crimped in for a better contact. Simply tightening these up can sometimes fix a reluctant motor.

Furthermore, the diodes for the control of the motor can be seen. These can fail, especially if the headlights have jammed at some point, overloading the motor. Sometimes the failure can be obvious, as the diode will have blown apart, or will disintegrate at the touch, but the best way to check the diodes is with a diode check function on a multimeter. These can be replaced by anyone handy with a soldering iron, and cost mere pennies at Radio Shack. Looking at the Radio Shack and other electronics catalogs, all available diodes will handle the low voltage (14VDC) and current (about 10 amps) of the motor, so selecting a replacement diode simply becomes a matter of finding the smallest one that will fit in the place of the old one.

The motor, as stated, is very reliable and is unlikely to fail; if the headlights pop up and down numerous times before staying in the appropriate position first suspect a bad or sticky relay, or faulty diodes, before the motor itself. If the relay and diodes check out good, then remove the circular cover plate from the motor gearbox. On the inside of the cover plate will be seen the switching paths for the motor raising and lowering; clean these well and re-grease the gears with good fresh grease, then reassemble and see if that fixes the problem.

Later cars, the 931 and 944 in particular, seem to have been put together without the grease. These can fail in a very frustrating way, wearing the gear on the drive shaft right out with a hollow spot where the gears can slip past eachother if presented with any resistance. In this case, the only option may be to replace the gear itself. Since this is not available by itself, a new or used replacement motor may need to be replaced. However, there is one more option to try first.

On the face of the gear opposite the driveshaft can be seen the contacts that control the motor. These are pressed on to and through the gear with metal tabs. The metal and plastic discs can be removed by prying between them and the phenolic gear face with a knife. Note the indexing of the discs relative to the flat spot on the gear, and rotate them relative to eachother, then reassemble (press back together 120 degrees off the original position). This could relocate the area of highest torque need to a different, less worn area of the gear, allowing it to work again. The motor can then be reassembled in reverse, and tested.

Finally, the headlight motor gets its power and switching signals from the headlight switch. If there are still problems, make sure that the headlight switch is functioning properly and that the correct currents are being passed to the motor connector. Refer to the Haynes manual for the appropriate wiring diagram for your year and model of car.

3 - Speedometer

Many reports of erratic speedometer operation come in. Kevin Fraser has kindly researched this problem and provides the solution below, from Porsche Tech Support:

"Dear Mr. Fraser,

The problem that you are experiencing with your speedometer is a common one among all models Porsche automobiles. As the vehicle gets older, the speedometer has become ‘trained’, as it were, to display only speeds that are in the range of the average speed of the car. In most cases, the average speed of any Porsche automobile is 200kph or 120mph. Therefore, if you drive at a speed slower than average, your speedometer becomes ‘confused’, as it is not used to driving at such a pedestrian like pace. Your options are: 1. replace the speedometer and ‘train’ your new one from scratch or 2. keep your existing speedometer and drive at a speed at least 160kph or more.

Sincerely, Claus Enoff Technical Support Dr.Ing.h.c.F.Porsche AG Porscheplatz 1 D-70435 Stuttgart"


4 - Relay and Fuse ID/Locations

The majority of the fuses and relays are located in the main fuse/relay panel under the dash on the driver's side, above the driver's feet. The fuses are clearly numbered, corresponding to numbers provided in the circuit diagram shown in Haynes and in the factory manuals. However, there are a few annoying exceptions! There are the auxiliary fuses, in a secondary/auxiliary fusebox just above the main fusebox. Michael Brown has been kind enough to tabulate their assignments:

Relay Locations, (confirmed for 81-onward 931 only):

(Top Row, left to right)

1. Not used
2. Fuel pump relay
3. Fog Lamp Relay
4. Not used
5. Seatbelt warning buzzer relay
6. Rear window defroster relay

(Bottom Row,  left to right)

1. Not used
2. Driving lights
3. Horn, rear wiper, adjustable mirrors relay
4. Wiper relay
5. Turn signal flasher relay

Additional Fuse Panel 79 and on 924's:

1. 8A Horn
2. 25A Warm-up Regulator, Auxiliary Air Valve and both Fuel Pumps
3. 16A Fan resistor, Fan Relay, and Fan Motor
4. 25A Rear Window Defogger Relay
5. 16A Cooling Fan relay on dual fan setups
6. 25A Air Conditioning Relay
7. Spare
8. Power Windows
9. Spare

Additional Fuse Panel 79 and on 931's:

1. 8A Horn
2. 25A Warm-up Regulator, Auxiliary Air Valve and both Fuel Pumps
3. 16A Cooling Fan resistor, Cooling Fan Relay, and Left Radiator Fan Motor
4. 25A Rear Window Defogger
5. 16A Cooling Fan relay, right radiator fan
6. 25A Air Conditioning Relay
7. Not Used
8. Power Windows
9. Not Used

Finally, the power window relay - where is it??? According to Lars, on his car it is located up under the dash near the steering column and the OXY sensor unit. It should have a fuse incorporated into its construction that may need to be replaced if your power windows have stopped working. On 931's, it appears to be clipped to a metal brace above the center hump, on the driver's side, like the relay for the radio (often not present anymore).

5 - Heater/AC Blower Fan Upgrade

A common and major pet peeve, once you've got your 924 running and are driving it around on a daily basis, is how weak the blower fan is. To clarify, we're talking about the fan for the inside heater and defrost. It always seems pathetic. So, naturally, once you've made sure that it's getting as much voltage from the wiring as possible, and it's got a good ground, and you're still not getting enough out of it, you want to know how you can upgrade it. Revis Rose had the following to say about the possibility of swapping in a more modern 944 blower fan.

The Series 1 944 was a fat-fendered 924 with a new motor. There was little change in the interior. Looking the units side by side they are very similar, with the prime difference being the fan itself. There also isn't a flapper door on it. It mounts in the same way as the 924 unit. It  will only blow air as good as a 944 Series 1, which is not as good a Series 2 car, but better than a 924.

It's important to note here that we're talking about the fan from an '83-85 944, not and '85.5 or later 944. The mid-year 944 model change brought with it a whole new interior, much more modern, with completely different heater/AC layout. As a result, components will not swap back-and-forth. This also means that the dash in its entirety cannot be swapped over, as the underlying body structure is different and it will not fit.

Some others have attempted this swap, unsuccessfully. This may only work with very late (late '82 and onward) 924's due to sheetmetal differences. Attempt this upgrade at your own risk.

6 - Dim Dash Lighting

The quality of the lighting used in the dash (and the center console gauges) is a common source of complaint for many new 924 owners. The lights are just not bright enough to overcome ambient lighting at night. There are a number of things that can be done. First of all, clean and/or replace all lightbulbs. The stock replacement is a Sylvania/GTE #37  or equivalent, puts out 1.2 Watts. However, by replacing these with Sylvania P/N 2723 or equivalent, you'll get a substantial improvement; these are 2.3W. Secondly, make sure the dimmer switch is clean inside using TV tuner contact cleaner. The current passes through a variable resistor (the thumbwheel in the main light switch) to change the brightness, and these contacts can get corroded and reduce the output. Finally, if the lights are still dim, you might be well advised to add an additional ground wire into the ground harness for the dash. Go behind the center speaker and the center console both, consult the wiring diagram in the Haynes manual for the correct color coding on a ground wire (such as for the gauges, it's a shared ground for gauges and lights, usually brown), splice into it with a heavy wire, 12GA or better, and run this to a crimp-on ring terminal, which can be attached to the center dash mounting stud behind the center speaker. This will also have the added bonus of improving the ground for the gauges, thereby improving the accuracy of the readings.

Using the extra bulb in tail-lights

From: Charles Ditmore
How many of you guys are using the extra socket in your tail light assembly? I wired mine up to come on with the headlights to make the car a little more visible at night. It is a pretty easy conversion if you have an extra bulb holder. Just put the bulb holder in the extra hole in the removable plate and splice it into the wire going to the tail light. looks pretty cool, I think.