Brake Lights Out
>Found out this weekend I have no brake lights working (almost got
>rear-ended Friday night at a stop light, now I know why). I tried to trace
>the problem over the weekend with no success.
Test the fuse first and if that's not the problem, check this:
On the master brake cylinder you'll find two pressure switch connectors. Disconnect and clean the contacts. This did the trick on my '78.
It's probably the switches, but you might want to check your "lamp control unit" also. It is behind and above the fuse box. All that is in there for the brake lights is a current sense circuit for the warning system. Works like this. Power comes from fuse 7 to the brake light switches (2 of them working in parallel, you need both to carry the amount of current. from the brake light switch to the control unit pin 1 (you should have 12 volts here when the brake is pressed, I think you need the key on). In the control unit it splits, goes through two sets of windings so that the warning system can sense both bulb currents. 12 volts comes out 9 and 12 and goes to the bulbs. I know this because my car had no brake lights when I bought it.
Pointers: don't pull the plug to test for 12v at pin one. get some speaker wire and strip the end, stick it in the connector for pin one and reassemble. you need the load to test the brake light switches. They will look good otherwise, but will have high resistance. another way would be to do a resistance test between fuse 7 and pin one of the harness, key off press the pedal it should be around 1 ohm. If it is the switches replace them both, one wont last. I bought real Porsche replacements, but later found out VW garages sell the same thing for a lot less money.
1978 928 5-speed
Guards red/black/tan sheepskins
928 OC Charter Member
I put in the cheap VW hydraulic brake light switches a couple of years ago and learned that when they both leak the hydaulic fluid there is no backup brake system aside from hauling up on the emergency brake. I posted the incident on 8/10/98.
When and if you replace the switches, make sure they are of the highest quality!
'82 928 5 speed 226k
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