Instrument Panel Light Replacement
Replacement of Instrument Panel Lights Indicating Automatic Transmission Shifter Location
(performed on ’87 S4)
Eventually, most Porsche 928’s with automatic transmissions have one or more of the gear selector location lights (right side of Tachometer) fail. Replacement of these is somewhat complex and requires careful work, but it is not an impossible task. The following write-up summarizes procedures developed by Earl Gillstrom and Gary Knox to replace the P and D lights in an ’87 S4. Both of these lights failed at ~84k miles when the instrument panel was shipped via UPS for odometer repair (these are apparently the only
two that fail early, as they are the most frequently illuminated).
(1) Remove the instrument pod from the car (other write-ups available for this, seek out the one that works for you and your car).
(2) With pod upside down, remove the two bolts on each end of the instrument panel. A 5-mm Allen wrench/socket is required to remove these. (As these are different, we recommend that after removal, you re-insert the bolts back into the pod at their respective ends to minimize errors in replacing panel and the pod when repairs are complete. And, Gary strongly recommends that you make an alignment mark on the offset/cam aluminum piece on the right side of the pod and on the attachment point at the pod before loosening that bolt. This will allow you to relocate it in exactly the same position when reattaching the instruments to the pod. Trying to correctly orient this piece and tighten the bolt while you are installing the pod into the dash is a real pain BTDT!).
(3) Remove the 9 Phillips head screws on the perimeter of the back side of the instrument panel. Carefully lift the instruments away from the frame and the transparent front "glass". Pull the 8 wire pigtail
through the opening in the back of the frame.
(4) There are 3 "slot head" screws and five 8mm hex nuts that hold the Tachometer to the back side of the instrument panel. Remove all these screws and hex nuts. Carefully hold the Tachometer so it does not fall away from the frame, then carefully pull it away from the frame, gently removing the "pigtail" of 8 insulated wires from the slot bracket in the frame and feeding it out through the opening on the right side of the Tachometer.
(5) Carefully remove the 3 screws on the back side of the Tachometer and the 2 screws on the outer edge of the front face (DO NOT TURN the 2 screws on the back side that are recessed into small holes in the frame itself). This will allow you to slightly separate the Tachometer "head" from its frame.
(6) Lift the Tachometer head slightly off its frame, then use small needle nose pliers to remove the 5 connectors for the small insulated wires from their respective connecting posts - which are on the opposite ends of the 5 hex nuts you removed in step (4). (Note which wire goes to which post for proper re-assembly).
(7) Place the Tachometer upside down on a frame that will support it without damaging the surface or needle (we used a piece of 4" PVC pipe coupling ). 3-4 pieces of masking tape were attached to the back side of the Tachometer and the sides of the coupling to provide a fairly rigid work surface.
(8) Now, you can see the 6 VERY small incandescent lights that illuminate the PRND32 figures on the right side of the Tachometer. These are 12 volt bulbs, so - using a 12 volt DC power source you can CAREFULLY make contact on each side of the leads of each bulb for final verification of exactly which bulbs are burned out.
(9) The burned out bulb(s) may be removed by using small side cutters to cut the leads at the surface of the circuit board (do this carefully, and protect your eyes/face when cutting the second lead on each bulb as they tend to "fly" up from the cutting force).
(10) NOW, you are ready to solder replacement bulbs in place. We used Mini Lamps from Radio Shack. These are 12 volt, 25mA bulbs (part # 272-1141A, cost ~$1.25 each) that have slightly larger bulbs than the Porsche OE, but fit nicely in the slots provided. Clear bulbs can be used in all slots, as the green illumination of the D designator is due to a green filter in the Tachometer. When installed, these bulbs seem to give ~90+% as bright illumination in the selector designators as the OE bulbs.
(11) We left ~ 1" pigtails on the leads, stripped them back about 1/8" (these small diameter wires require specially sized strippers or very careful knife work), then placed the copper leads horizontally across the solder joints where the OE bulbs had been cut out. We did not insert the bulbs into the slots at this time, doing that in step (12). A small tip 25-30 watt soldering iron*, small diameter solder wire, small needle nose pliers to hold the pigtails in place, and 3-4 very steady hands are required.
(12) After each bulb was soldered in place, we checked to see there was no bridging of the solder, then verified the contacts were good and bulbs operative by using probes from a 12 volt source to touch the fresh solder on each side of the connection. After verification, we carefully placed each new bulb in its proper slot, used a little RTV to permanently position the bulb, then "smiled in relief"!
(13) We cleaned all electrical contacts, then reassembled the instruments, starting with step (6) above and working back through (1). After all of the instrument panel is reassembled, you might consider taking
out the three light bulbs at the bottom of the panel (larger black sockets, ~1/4 turn counter clockwise to remove) and dusting them off for brighten the illumination. (You would be better off in the long run if you replaced them now at a cost of <$5, as it will save a lot of work and possible profanity at a later date when the old bulbs fail and you have to remove the pod again!). The small black sockets scattered on the left and right of the instrument panel are for the individual warning symbols. These can also be removed for dusting but have such limited illumination time that they should last for a century or millennium!
(14) Before attaching the instrument panel to the pod, we suggest you connect all the wires from the dash to the instrument panel, then turn on the parking lights and ignition switch, and run the gear selector from P through 2. This allows you to verify that all of the lights work before you do all the work of reinstalling the pod. (Note that the 3 bulbs for general illumination of the instruments will not light unless the leads to the dash light potentiometer on the pod are connected to each other, or to the potentiometer).
(15) IF THE LIGHTS NOW "GLOW" CORRECTLY, CONGRATULATIONS, YOU DID IT - JUST AS WE DID!
* Radio Shack lists several small soldering irons in their catalog. Here
are some options worth considering if you do not already have one:
- a 25 watt pencil iron (#64-2070) for ~$7
- a 5 piece basic soldering kit (#64-2802) for $~8
- a fully equipped 11 piece kit (#642803) for ~$20
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