1984 Porsche 944 Engine Wiring Diagram

Upon removal of the dash and interior carpeting, a veritable rats nest of wiring is exposed. Before moving any further, I felt obligated to clean up the mess and ensure that everything was operational.

To perform any electrical work on a Porsche, you really must have a copy of the factory wiring diagrams. I find the Porsche wiring diagrams to be very thorough and, once you figure out their approach, very usable. I have been fortunate enough to purchase vintage shop manuals with all the wiring diagrams. I used to make do with a CD version of the shop manuals. With a little searching on the internet you can find these CDs for about $20. And some of the wiring diagrams have been posted on enthusiast's websites.

In general, the Central Electrical Panel (CEP) serves as the hub for the 944's electrical system. On the early cars, it is located in a rather awkward location behind the dashboard just above the driver's left knee. It consists of a rectangular box with relays, fuses, plug-in multi-pin receptacles, and male blade terminals for individual wiring connections. There is also a separate auxiliary fuse panel with xx fuses. It is not as elaborate as a 928 panel (see article here) and it also seems to me to be a little more "ad hoc" than the panel for the 928. Regardless, the basic concepts are the same. Main power in. Ignition key switched and non-switched power out. All circuits fused. High power devices like fuel pumps, headlights, sunroofs, fans, etc. utilize relays.

My three major goals were to 1) add a central "kill switch", 2) refurbish the system as required to achieve a high confidence regarding reliability, and 3) clean up all the "kludges" clearly evident as performed by prior hack mechanics.

A central kill switch is typically mandated by the various race sanctioning organizations. Typically they are not required for track day cars. That said, I like the idea that if the situation arises where there has been an incident and I smell gasoline, I want to be able to get the electrical system shut down as quickly as possible. You have probably seen the red handle on a kill switch sticking out of the body of a racecar. Having served my time as a corner worker, I understand the appeal of the corner worker being able to run up to the car and kill the electrical system as a first order of business. But then there is my one personal experience where at a DE event, my balance shaft bearing failed and I dumped oil on to the track and the car was enveloped in white smoke. Upon my later review of the incident, I realized the corner worker's first order of business was to wave his yellow flag and alert the entire field to the oil on the track, which undoubtedly considerably reduced the chances of additional cars slamming into me after they hit my oil. What the corner worker did not do was run over to my car and attempt to assist with my potential fire. I was on my own for many long minutes until additional help arrived. So I find that the placement of the kill switch within easy reach of me, the driver, adds to my peace of mind. And with that approach in mind, I proceeded to plan out a placement of the switch in the center dash board area.

I initially considered using the existing opening for the cigar lighter. I think technically the switch would have fit but it's terminals for the battery leads were too close for comfort to the HVAC controls. My final solution was to use the opening for the radio. This is still tight but worked out OK. I built a substantial mounting bracket and hard mounted the bracket and thus the switch to the top of the transmission tunnel. I actually re-purposed the existing bracket for the radio, which avoided introducing new holes and fasteners in the tunnel. I fabricated a light duty cosmetic blanking plate for the radio opening for the switch to protrude through. It looked a little lonely all by itself so I decided to add a USB port. Finally, to obtain a symmetric configuration, I added a digital voltage gauge. Surprisingly, the original dash did not include one. I think it's spot may get appropriated by the AC knob?

A brief discussion of how the kill switch works is in order. The kill switch rotates through 90 degrees and its primary job is to break the circuit between the battery and the rest of the car. But once running, you can remove the battery from the car and the engine will keep running. So there is a secondary function of the kill switch to kill the engine. Mine does this by interrupting the 12V current supplied to the ignition coil. This required 2 new harnesses. One harness consisted of heavy gauge leads from the positive terminal of the battery and back to the battery compartment, where it picked up the lead to the starter. The 944 also uses three 4.0 mm wires from the positive terminal of the battery. 2 of these are the primary feed to the CEP and 1 feeds the fuel pump relay. A second harness served this same function by running from the kill switch under the dash to the CEP and fuel pump relay. The 12V feed to the coil also originates at the CEP. I had to splice in a wire from the feed out and back to the kill switch, using the same harness as for the 3 electrical leads.

This represents a lot of work! The quick and dirty version, which you may see on budget racers, is to mount the switch in the fender right next to the battery. This just removes the battery from the circuit but does not guarantee that the engine will be killed at the same time.

Here are some photos. The installation is tight but when complete, it does not look totally out of place. And it is very easy for the driver to reach, even strapped in.

Next was reliability and removal of existing hacks. As with the 928, job one is to remove every "friction type" electrical connection and to clean off corrosion and prep the contact surfaces with an appropriate chemical treatment. The 928 community seems to swear by DeoxIT spray contact cleaner so that is what I use. I took a bunch of photos and proceeded to remove the CEP. First you remove 2 screws and drop the auxiliary fuse panel out of the way. The CEP is held in by 2 screws and once they are removed you can remove it from it mounting bracket and drop it down. Somewhat! There is not a whole amount of extra length to the attached wiring harnesses. Take more photos and a deep breath and proceed to pull the various wires and plugs. Eventually the CEP will be released and you can take it to the workbench for better inspection and cleaning.

I think I've seen someone, maybe Van Svenson, who dis-assembled the CEP. How to dis-assemble it was not obvious to me and I decided to forgo that step. I would note that later during electrical testing I did find one internal electrical connection within the panel that was dead. I was able to perform a work around. But if you were to be pro-active you might want to check for continuity within the panel, based on a review of the wiring diagram. Finding more than a few problems might prompt you to dis-assemble the CEP or find a replacement.

In the photo of the CEP, you can see that there are six white colored sockets that accept multi-pin plugs A through F. It may not be obvious but the sockets for these 6 plugs are uniquely "keyed" so that you can't put the wrong plug back into the wrong socket. There are 5 hard mounted sockets for relays on the panel. Although they are denoted J thru M, this terminology does not seem to carry over to the wiring diagram. I wound up using the picture in my original owner's manual to identify which relays went where. I used this same approach for the 5 relays that are externally mounted on a set of brackets cantilevered off the side of the panel. For the externally mounted relays, you can also easily see the incoming wires and use their colors and the wiring diagram to ensure which is which. It is not entirely impossible for the relay sockets to be relocated so I would highly advise this step.

For the fuse holders, I simply cleaned them with DeoxIT. These fuses are an older style found on European cars of this vintage that are typically denoted as "ceramic" or "torpedo" fuses. I was able to find some new replacement fuses on Ebay that used copper (versus tin) connectors so I proactively replaced all the fuses. I did not replace the relays, as most are specialized and very costly to replace with new relays. Even used relays can be expensive. Fortunately, I found all of mine to be in good working order.

An area where I struggled a little was the various "G" and "H" connectors. These are all male blade connectors that are grouped together on a corner of the CEP. My photos left a lot to be desired because it is hard to get a good shot in that location before you start pulling the wires. What I did was make a "shopping list" based on the wiring diagram of all the wires that connect here. The "H" leads are all non-switched power and you really can't go wrong with those. The "G" leads are numbered and as long as you match up the numbers to the correct colored wires, as shown on the wiring diagram, you should be fine. Be advised that you can and will find hacks in this area as folks have tried to tap in for power for stereos and what have you.

G and H terminals on the lower right hand corner of the assembly.

Butt splice connector

Speaking of hacks, here is a photo of a crimp type butt connector that I found on the main power feed for the fuel pump. It pulled apart in my bare hands! I know that when done correctly, to military or aircraft standards, that crimp connection are considered to be superior. My personal approach is to strip the wires, hook the ends together, solder the wires, and apply a cover of heat shrink tubing that extends well beyond the soldered joint. The heat shrink tubing serves to soften the hard point at the edge of the solder joint and minimize fatigue related issues later on. Here is a photo.

Soldered and heat shrink wrapped wiring connection

Related to crimped butt splices are Porsche's own factory connectors. These are a necessary evil in order to be able to assemble a car with wiring harnesses on an assembly line but they can be a source of trouble. Here is a picture of a connector I found leading to the electric window switches.

This is the end result of a vicious cycle where the connector develops corrosion, which increases the resistance, which results in localized heating, and ultimately failure. This is the only bad one I found on the car but I chose to used soldered splices with heat shrink tubing wherever I came across a connection that was passing substantial current. All of the low current connections were cleaned with DeoxIT.

Another area that must be attended to are the various ground points. The factory wiring diagram has a list of all the ground points. It will pay you to track down each and every one for dis-assembly and cleaning. I did. For example, here is a photo of a major ground point that is behind the CEP. You probably would never be able to see it much, less clean it, with partial removal of the CEP first.

Before reinstalling the dash, I attempted to identify and perform a functional check on all the required circuits, in particular those terminating at the dash or center console. The very first check, in order to avoid an electrical fire, was to check the resistance from the battery connection through the kill switch as various basic systems were put into play. At this time, no fuses were installed, so that I could gradually introduce/test these circuits on a case by case basis. Up to a point, the circuit from the battery to the CEP is not fused so if a short did exist, it would resolve itself by melting the associated wires. Not a good thing. So I simply connected my Fluke meter, set on resistance, to the battery lead, without connecting it to the battery, and made sure there was a reasonable amount of resistance as I engaged the various circuits. For instance, with the kill switch off, the resistance should be infinite. With the kill switch on, the resistance should still be infinite, as there should be few or no circuits that pull current when the ignition switch is off. A few exceptions might be the memory circuit for a radio, interior lights if the doors are open, or an alarm. As this car doesn't have a radio or an alarm, and the interior lights were not connected yet, there would still be an infinite resistance. Once the ignition key is put to the run position, quite a few resistances are introduced. What you are doing is looking out for any dead shorts.

BTW, the ignition key on this early car has an interesting feature. Simply inserting the key closes a switch in the ignition that can power selected components. This would be similar to the Accessory position some keys use. In the case of my 944, the only items I could find that were activated by this key position was the radio and the "remove" mode for the sunroof.

Once I gained confidence that the basic circuitry was sound, I hooked up the battery and started testing for actual voltages. This is a better approach, as you can check for voltage drops due to unacceptable high resistance connections. And you can start to check relay function.

Using a photocopy of the set of wiring diagrams, I slowly and methodically checked for proper operation of all of the required circuits. As described above, I started with the direct unfused circuits. Then I gradually added fuses one at a time and checked for the proper function of that associated circuit. The two that I recall that gave me the biggest headaches were the sunroof circuit and the electric windows.

Clarks Garage has a very good writeup regarding the operation and troubleshooting of the sunroof. As others have noted, the 944 sunroof is probably not Porsches best design effort. In retrospect, I had multiple issues with the sunroof. Some mechanical. Some electrical. Repairs included taking the drive motor completely apart several times until I could get it to operate upon direct application of voltage. It turned out that one of the two wires feeding it voltage was barely working at a mechanical butt splice. When I removed the splice, the remaining wire was so short I had to add new wiring and connect it inside near its connection to the brushes. I removed all the old grease and packed it with new grease. After all this, it would spin just fine with no load but could barely budge the sunroof drive mechanism. This initiated a complete dis-assembly of the drive mechanism, cleaning, and lubrication with new grease. After this, friction was reduced enough for the motor to be able to raise and lower the roof. Still more work was need to set the 3 limit switches to their correct positions. The final insult was that a new genuine Porsche gasket installed around the perimeter of the roof resulted in so much new friction that the motor could not fully close the roof without assistance. I finally wound up going back with the original gasket. Now the roof will open and close. It was quite the challenge.

The power windows had an interesting twist. After my episode with the sunroof motor and noting that the motors for the power windows were very similar, I went straight to cleaning out the old grease and packing in new grease for the drive gears. The motors worked very well when powered directly but I could not for the life of me get them to work off of the door switches. I finally went and found some switches that I had salvaged from a parts car and tried them. Things worked perfectly!! As far as I can tell, the door switches that came with the car had a subtle difference in part numbering such that they were wired internally differently than what was required. Maybe they came off another model car, I don't know. Once I found the problem with the switches, all the problems were resolved.

One of my goals was to label the various wires and connectors, especially those that plugged into the dash and center console. As part of the trouble shooting and testing process, it was a simple step to use my label maker to tag the various components. As I found when I finally re-installed the dash, this greatly simplified things.

There are several relays that are not mounted at or near the CEP. Most are mounted in the area between the heater/AC housing and the steering wheel column. Oh, an interesting factoid about the sunroof relay. It has a function that reads a signal from the speedometer and locks out the sunroof from the "removal" position when the car is moving. Interesting.

Another item of interest is that some of the 944 electrical components cross reference to more generic mass production part numbers. For instance, I bought a new fan motor, a new ignition key electrical switch, and a new switch for the heater fan motor at very reasonable prices using VW part numbers. I found it helps to enter the Porsche part number in Google or Ebay and see what pops up. There are few auto dismantlers out there that have pretty good websites that will take a Bosch part number and show all the vehicles it will work on. The fan motor was actually missing on my car. I bought a new one for $30 and it was a perfect fit.

Switch for the ignition key

While I was in there, I replaced most of the small bulbs in the instrument lights with new ones. I also replaced all the bulbs in the tail light assembly. The head lights had decent quality halogen bulbs in them so I left them as is. The mechanism to raise the head lights is working but several of the bushings are worn out such that when closed they are not even. I have purchase the new bushings from Paragon Products. Their future installation may be the subject of another post.

So it's still a 30 year old car. But wires don't wear out, it usually just the stuff at the ends of the wires that cause problems. With the restorative and preventive maintenance that I've done to the electrical system, hopefully that will be one less thing to worry about when this car gets back onto the road again.

Source: https://newhillgarage.com/2017/01/04/1984-porsche-944-streettrack-car-electrical-refurbishment-and-kill-switch/

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