Electrical maintenance - Lesson learnt

J

John Larkin

Member
On January 14th my wipers and heater stopped working simultaneously while driving in rain. I discovered later that my heated rear screen had also stopped working.

These three items receive their power supply in common from the ignition switch. There were no blown fuses. After testing I discovered that the wipers and HRW worked if I removed the heater fuse, so I suspected a short to earth in the heater. I discovered that two of the three wires (one power, two earth via heater speed switches) had a few copper strands protruding at the bullet connector block in the engine compartment. I renewed the connectors and everything worked again --- for about ten minutes when the heater motor and HRW failed again, but not the wipers!

I could find no breaks in cables, no loose connections, etc, etc. But I eventually discovered that the power supply to the wiper fuse is connected to one only of the two clips that hold the fuse at the power connection. In other words, the metal cap at the end of the wiper fuse carries power to its matching clip --- these are separate pieces of metal. This second clip is connected to the power end of the heater fuse and from there via a cable to the HRW fuse. I polished the ends of the wiper fuse and all its four mounting clips and everything works again. I polished every remaining metal connector on the fuse board (Dremel + stainless steel wire brush). The heater sounds stronger, the wipers are faster, the indicators rejuvenated. I did about a hour's driving with the heater running.

LESSON: Clean your fuse box connectors. Even if your fuses and connectors look clean they may be adding resistance or even failing to carry current.
 
Hi John,
Had a similar problem, but with intermittent iterior light operation, a good cleanup of all the fusebox connectors (emery cloth, didn't think to use the dremmel, would have made life a lot easier!) and hey presto all is fine!
Cheers
AL
 
And me! I had the same problem with a blown panel light fuse took it out and then carried on testing the newly connected electrics and the brake lights/indicators and tail lights stopped working. Like you say the fuse has to be in place to supply power to the adjacent fuse.

Not obvious at all that it should be connected like this. I spent a few hours piddling around with the rest of the wiring before the problem became apparent.

Well done for pointing it out John could save people a lot of hassle with that little bit of knowledge.
 
I had headlight problems traced to the fuse box - so much heat caused by loose fuses had caused the plastic to melt.. making things worse. A new fuse box is on the list ( a way down the list) I thought I had sorted all the problems until one of the dip beam wires fell off the fuse box - again as a result of the heat the wire has become brittle . I took the wire back to good cable and crimp& soldered in blade fuse holders for now.
Then I went and check the fuse box in my 2000sc... all ok.
 
I forgot something that scauto reminded me of ...

One of the fuse connectors ( I can't remember which) had partially melted some adjacent plastic. This is a sobering reminder of how easily hundreds of manhours and thousands of pounds expenditure could be lost in a fire even in a car you believe that you are pampering. I would never have thought of checking or cleaning the fuse box if these electrical problems had not arisen. Uhhh... I shudder at the thought.
 
A NZ Rover club newsletter article this month reminded members of an inherent fire risk posed by the fuse box fitted to Series 2 P6's. This item is located in the glove box.

It was claimed that loose fuse holders can generate heat which can be capable of melting the fuse box's flimsy light plastic. This risk is exacerbated by the use of under-sized fuses due to the scarce availability of full-length Imperial links and loose crimping of the wiring loom to the contacts on the rear of the fuse box itself during production.
 
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