Electrickery

The MoT was passed without even an “advisory”, but a couple of days ago a few minor electrical gremlins cropped up.

The horn packed up again, and at the same time I also intermittently lost the headlight flash function, though main and dipped beam worked fine. I suspected the indicator stalk had failed as it’s the only common part to both circuits, and I’d not long ago replaced the blade terminals on the feeds to these two functions when the horn failed previously, but the outputs of each switch function showed power.

Trying to find the exact failure point again proved elusive. My simple voltage reader picked up power at the end of the horn circuits where the wire connects to the horns themselves, but the horns would not sound. Running a bypass wire from the battery terminal direct to the horns sounded them (very loudly), but a check with the switch again was still silent. I ran a bypass from the output of the horn switch to the horns with no effect. I then bypassed the switch from the fuse box terminals, again met with silence. The switch was replaced with the new one I bought before I managed to repair the existing one last time, but this made no difference.

I was pretty stumped, with both high beam and dipped circuits working fine, and the horn working when run directly from the battery, and the switch outputs of both faulty circuits showing power with both the old and new switches, with no faults in the wiring between the switch and appliances. I eventually found the cause – the blade terminals on the fuse box to which the horn and flash were connected were dulled with age, though they looked reasonably clean. Scrubbing them up with emery cloth immediately restored full function, and I cleaned all the other fuse box contacts too to make sure no other circuits were affected. It looks like there was permitted but limited current through the dirty contacts which provided a voltage reading with no earth, but once the circuits ran to earth through the appliances, the amount of current available was too little to operate them.

I have also had a failure of the off-side wing mirror heater. The heater pads are self adhesive plastic sheets with a double element running to and from blade connectors in the centre of the pad. The construction of the pads is of two-ply plastic laminates, with the elements sandwiched in between. The terminals are stamped in through the laminates, as soldered joints are not possible, and are flexible to allow easy connection. However, one of the terminal tags tore off, possibly due to vibration or the supply wire being tugged.

Repairing this has been very time consuming and has met with limited success. The method I used was to create a new tab, using a “length” of the elements’ zigzag, and carefully peeling away one of the plastic laminates to expose the metal. A female blade connector was then fit over the elements and compressed to stay in place, with special window heater element repair paint applied to the joint to ensure good contact. While I have good contact when tested on the bench, the mirror doesn’t seem to be working properly once refitted. Hopefully, I’ll find the problem and get it working again, but I’d like to avoid the expense of a new pad if I can – they only seem to come in pairs with the rest of the kit, and aren’t terribly cheap. They’re a very good accessory, though, with significant safety benefits, so I will persevere.