Electrical eccentricities
With a new petrol tank fitted, the TR7 runs again, so I’ve started the long-planned electrical refresh. During the 1970s car electrics became more complex; German and Japanese manufacturers were improving reliability, but the same can’t be said for the British car industry. Sweeping generalisation perhaps, but TR7 electrics fit this theory.
Battery fully charged, I checked which electrical items actually worked. After ten minutes a long list of faults had emerged. It’s also apparent that haphazard additions have been made to the wiring over the years; an unknown red wire spliced to black earth wires is a worrying example.
The 7’s electrical nerve centre lies behind the glovebox, where numerous fuses and relays are buried. Relays control various essential components, but identifying them is difficult. Armed with a wiring diagram, the cable colours soon showed which was which. Next, I replaced all fuses with new ones of the correct rating, gently cleaning the fusebox contacts at the same time. Moving to the steering column, the cowl was removed and the switches sprayed liberally with contact cleaner. A quick check showed this had made no difference whatsoever to the nonfunctional circuits, but at least I now had a sound basis from which to continue.
Electrical chaos or work in progress…
Concentrating on the inoperative horn, I replaced the relay – no difference. Running a test wire direct from the horn and touching it to the battery positive terminal gave a reassuring beep, so the horn itself was working. Moving back up the circuit stepwise, a test wire from horn relay socket to battery produced a beep, so wiring to the horn was also intact. Checking the voltage
supplied to the input side of the relay showed zero. No volts at the fuse terminal supplying the relay either, but there was power at the other end of the fuse. I pulled out the brand new fuse, finding one end cap slightly loose. After inserting another fuse, the horn worked perfectly. The first fuse had a dry solder joint inside and couldn’t conduct the current drawn by the horn. The clock and interior lights run on the same circuit, so three problems were ticked off my list.
Now for the hazard warning lights. From wiring colours, I found which of the two flasher units under the dash operated the hazards, but strangely it had three pins, not two as shown in the diagram. A new, two pin flasher was quickly connected, with the third DIY earth wire left dangling. And now the hazards worked perfectly. Why, oh why was it necessary to use the wrong flasher, adding an extra wire in the process? Such bodging confirms this electrical overhaul is essential.
Next up were the indicator side repeaters. The main wires to the indicator/sidelight units were easily found under the wings, with a ratty-looking loudspeaker cable leading towards the side repeater, but connected to absolutely nothing. I fitted new, correctly coloured wires for the side repeater, but need to source new bulb holders to complete the job. While under the front of the car, I located the main loom wires feeding the fog lights. It was no surprise to find these connected to… nothing! The fog lights should be an easy fix.
And that’s as far as I’ve been able to get this month. Progress has been encouraging and the electrics should soon be fully operational. Meanwhile, the twin SU carbs on the Sprint engine show signs of amateurish attention, with no gaskets fitted to the float chamber lids. I’m looking forward to rebuilding the carbs properly and giving the engine a thorough tune-up.
Haphazard additions to the wiring have been made over the years