Porsche Repair: 1992 968 Cooling Fans, jumper wires, jumper wire

Question
Dave,
THe cooling fans in my 1992 968 constantly run.  This has just started within the past week.  If I remove and replace the relay, they stop.  I had a 89 944 that did the same thing and the problem was the temp sensors.  This happened with the 968 again today.  I tapped on the relay and the fans stopped.  Sounds like the relay.  Is there anything else I can do to check this?

Answer
Hi Kirk,

My wiring diagrams don't get into the '92 range so I'm flying blind a bit.

But your 'tapping on the relay' test is a HUGE clue.  Let's just test the relay and prove it's good or bad.  I hope you have a voltage meter.

Test 1.  Take the relay over near the battery.  Find two jumper wires and strip their ends.  Connect the ends of the jumper wires to the pos and neg terminals of the battery.  Connect the other end of either wire to the relay's #85 terminal.  Take the loose end of the second jumper wire and touch it on then off the #86 terminal of the relay.  When you touch and make the connection with the #86 terminal you should hear an audible click inside the relay.  If so, the relay is working, at least based on the way relays are typically tested.

Inside the relay the "click" you hear is indeed two contacts snapping together and making an electrical connection...sending 12v+ to the fan motor(s).  The "normal-acting" relay will release this connection as soon as the #86 connection is broken.  I don't believe this release is audible.  But it can be "seen" if you measure voltage.

Test 2.  You'll do Test 1 exactly as above... along with a voltage tester connected this way:

Voltage tester probe A connected to neg terminal of the battery.  Voltage tester probe B connected to relay terminal 87.  When you do test 1, the voltage tester should register 12v+ when #86 is touched and as soon as that connection is broken, the voltage should go to zero.  If so, the relay is perfect.  If not, the relay is toast.  If it indeed stays at 12v+, you have a very special, very untypical and extra strong relay...but of no use to you.  It's a freak.  Throw it away but don't let the kids around it..it seems to have a mind of its own.

Do all this and let me know.  I'll be curious what you find.

Dave