Greetings. My 86.5 928S manual (US-spec) has an intermittent problem where it fails to detect the opening of either door or the hatch. The interior lights don't come on, and the rear hatch release fails to cycle, just as if the doors are closed.

On my other cars I've had problems with the interior light/horn/hatch-release fuse blowing, and with the spring loaded (driver's side) door switch, so I started there. But the fuse is good, and I found all the doors/hatch switches fail similtaneously. And then start working (together) again later. Usually. Though they didn't work last night or again this moring.

I searched the forum, but didn't find a problem quite like this. The maintenance/repair area where I'm weakest (by a wide margin) is electrical. So if you have any advice on where to look for further trouble shooting, my apologies in advance for any child-like follow-up questions and understand.

Thanks,
Christopher
1990 s4 Dunkle Blau (the "black" 928)
1989 s4 Stone Gray 5-spd (sadly left in the USA)
1986.5 S 5-spd Grand Prix White

 

I would start by checking which of the doors, when opening has the problem. Could be the switch. If not at the switch, check every bulb harness. When a door open, you should have battery voltage from + to the ground. Narrow down, and find the fault in the wiring/connection. Do your rear hatch switches function normally ?

 

'86.5 is the first US 928 model that has a relay for the interior lights. If both doors are experiencing this intermittent symptom at the same time, it's probably not the switches and may be the relay instead.

Dan
'91 928GT S/C 475hp/460lb.ft

 

Thanks. I'll check that relay when I have some light tomorrow. I tried opening the doors and hatch multiple times tonight, and the lights never came on. Though previously I thought the interior lights worked when I switched them to always-on mode? Well whether that was true or not, none of the lights worked at any setting tonight. And it was a dark night in my Belgian village...

Cheers,
Christopher
1990 s4 Dunkle Blau (the "black" 928)
1989 s4 Stone Gray 5-spd (sadly left in the USA)
1986.5 S 5-spd Grand Prix White