pacovinoly

I may be starting to lose my mind so please tell me if I'm crazy. And my apologies for rambling on but I want to describe my situation as best as possible.

I have a 1987 928S4 Automatic.

All of this started the other day when one of my right side brake light went out. I went to AutoZone and got the replacement bulb, Sylvania 7506LL. I replaced the bulb, all good, but then the problems started and I'm not sure how related they are to each other.

• First, my white backup lights stopped working. This turned out to the a blown fuse #12. Fixed.
  
• Then my left side rear parking lights, the two red ones next to the brake light, stopped intensifying when I press the brake pedal. The right ones worked fine. They come on when I turn on the headlights and get stronger when I press the brakes. The left don't do that. I'm assuming intensifying is the normal behavior, but I had not thought of it before.
  
• I figured I probably should've replace both break lights at the same time, so I did that, checked the grounds, unplugged the battery and checked all the fuses. That didn't work.
  
• Back to AutoZone where I decided to replace all the rear parking lights. I got the Sylvania 5007LL and replaced all 4.
  
• Now the lights come on with the brake pedal being depressed, but after a few seconds I get a "Tail light" warning on the dash. I figured something is happening as the light warms up but that's just a guess. I left it like this for a while.
  
• The next day, I started blowing fuses 40 & 41 (rear side markers). This took out all my parking lights, so when I turn on the headlights, no other marker lights or taillights go on. They only come on when I brake.
  
• Replaced the fuses twice and took out the 5007LL bulbs and back to the original ones that were in there.
  
• Now my 3rd brake light is on all the time. All the lights are on and barely increase in intensity when the brake is applied. This doesn't seem right.
  
• To top it off, a couple of days ago, my front yellow side markers were blinking in unison with the turn signal lights. They've stopped now, but I have no idea how that could even be possible. That's when I thought I might be losing my mind.

I've checked the grounds, the fuses, reset the battery and tried replacing bulbs. Could it be the relays? Is there more I can check? Do I need a whole new electrical system? It's all starting to feel like it's random and I can't even explain it so that's why I think I may be losing my mind.

I'm also trying to fix the cruise control and the A/C but I wonder if they may also be related to my electrical issues. One at a time...

Thanks in advance for any help and please let me know if posting any pictures of the issues would help explain my situation.

Thanks.

borland

Your problem seems to be related to installing the incorrect bulbs. The brake lamps and the front turn signals require dual filament type bulbs. All the rest (marker, third brake light, tail lamps) require single filament bulbs. If you install single filament bulbs in the brake light sockets, the problem you describe will occurr.

7506 is a single filament bulb for use on third brake light. Take a look inside the bulb socket to see if it matches the bulbs to be installed.

pacovinoly

thanks borland. excellent point. i completely overlooked that.

the issue is that the recommended bulb was the 7225, which does have the double filament, but the pegs are not aligned to allow it to fit into the bulb holder. the 7506 was also on the list and fit fine, but you're right, that's only for the 3rd light as it's a single filament.

would you know which is the right bulb for the brake light? the Sylvania site was recommended on Rennlist but I'm not sure it's 100% accurate now.

if the taillights are single filament, should they not be intensifying when I press the brake pedal? i'm not sure I know what's normal behavior anymore.

i will try to find and put the proper bulbs in the brake lights tomorrow and hopefully that will start to fix some of the issues.

thanks again borland!

pacovinoly

this is what i found, but I can't get the 7225 to fit into the bulb holder. i feel stupid now as i'm sure i'm missing something.

1987 Porsche 928 Car Light Bulb Sizes Chart

High and Low Beam Headlight Bulb Size: 9004 or 9004 HID Upgrade Kit
Parking Light Bulb Size: 5008
Front Turn Signal Light Bulb Size: 7506
Rear Turn Signal Light Bulb Size: 7506
Tail Light Bulb Size: 7225
Stop Light Bulb Size: 7225 or 7506
High Mount Stop Light Bulb Size: 7506
Fog/Driving Light Bulb Size: H3-55W
License Plate Light Bulb Size: 6418
Back Up Light Bulb Size: 7506
Front Side Marker Light Bulb Size: 5008
Rear Side Marker Light Bulb Size: 5008
Instrument-General Light Bulb Size: 2721

Bilal928S4

IIRC the dual filament bulbs have the stubs very slightly at different depths. It is possible to install the bulb 180 degrees off.
Also the german cars do not fare well with the american made bulbs. I have seen this on the BMW as well as the porsche. Something to do with too much resistance or something.
Hope that helps.
Bilal

pacovinoly

Thanks Bilal. I think I figured it out. You're right, the pegs are at different depths and offset from center.

So, I took Borland's advice and pulled the bulb from the front turn signal, as this would be the other double filament bulb. It happens that this bulb is 7528 NOT 7225! The stubs are reversed in the 7528 allowing it to fit easily into the base. 7225 is NOT the correct bulb for my 87 928S4 as the Sylvania website says.

I'm off to AutoZone again to see if the 7528s work.

Thanks!

pacovinoly

The 7528s work! All problems solved. Thanks guys.

ramcram

The double fillamet bulbs have 2 different wattages, brake and parker, for example. The offset pin heights are to stop you fitting them the wrong way and getting a really bright tail light and a not so bright brake light [that wouldn't be seen well in day light].
IMHO always change your bulbs in pairs or sets as the bulb failure system works by detecting differen resistance, one side to the other and when it compairs a new bulb to an old one, they rarely match.