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Wiring Loom
This was a part of the project that I was very much looking forward to as I had decided fairly early on to construct my own loom.
The starting point for the wiring was the MGB wiring loom from the Haynes Manual in conjunction with a site I found on the internet. The diagrams are in pdf format at Advance Autowire website and show many different variations by year. They are all colour coded and are very easy to follow.
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I wanted to make a few changes to the standard 1971 MGB wiring specification, specifically with regard to fuses and relays.
There are no relays on the MGB and only 4 fuses so I designed in 8 fuses and 4 relays(Spotlights, Main Beams, Headlights and Horn) to protect the car from switching large currents through the low current switches.
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I attached some cable ties with bases on the back of the dashboard and inside the engine compartment and body. With rough measurements and 10% added I ordered relevant cables and connectors from Vehicle Wiring Products in Derbyshire.
I started with the ignition circuit primarily so that I could start the engine. The cables were run through the loose cable ties and terminated with pre-insulated terminals. I had two multi-way mate-n-lock connectors through to the engine compartment, one 15 way and one 6 way.
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To connect to the rear loom I had a 12-way mate-n-lock connector. I also used an 8-way multi-way connector for the steering column switch to allow it to be disconnected from the loom.
I then progressed to the instruments, switches, lights horns etc. etc. After all of the cables were in place and tested I bound the looms with non-adhesive loom tape to make the job neat and I fitted grommets where the cables went through the body.
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Switches
I used Lucas switches for the lights and wiper with Lucas "style" switches for the spot lights, rear fog light and heater fan. The replica switches don't completely line up although not such much that a glance at them would indicate. At some stage it might annoy be enough to invest in OEM Lucas switches.
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The overdrive switch is a standard MGB item, although not included on my MGB donor. I chose the curved one off an early MGB as I think it looks the part when combined with a stainless steel escutcheon plate.
I used a 19mm stainless steel pushbutton for the washer pump and an aftermarket hazard warning switch. This was designed into the loom along with the flasher unit.
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The indicator stalk was modified and I (well my Dad again really) made a stainless steel crank and handle.
The handle looks great although it is a little heavy so I would recommend using aluminium if anyone else made their own. I also made an aluminium block to fit on the shortened original indicator stick. This was held in place with small grub screws in tapped holes that I drilled. Also the new crank was attached to the block in the same way.
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Instruments
The instruments are all standard MGB units for my 1972 car. I stripped them and cleaned them up. The oil pressure/water temperature gauge was damaged and would need reconditioning. It was only a little more expensive to buy a brand new one so that's what I did. That gave me a Celsius scale rather than the C-N-H indications on the original.
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The original speedo was stripped and zeroed. It will need calibrating prior to SVA. The theory I am using is that if I remove the needle, run the car to a known speed on a rolling road, then push the needle back on in that position plus a bit, it should be quite accurate. Hopefully my theory will work.The tacho is the 3 connector version. A switched live (white lead) comes from the ignition switch to a bullet connector. That goes through an internal coil and comes out via another bullet connector. This then goes to the coil. A green wire from the switched and fused circuit also goes in to provide power to the circuitry.
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Lights
The indicators on the dashboard above the steering wheel were after market items and were for indicators, front spot light, rear fog light and brake fluid level. I had to buy instrument backlights from Moss.
The exterior lights were all bought from Stafford Vehicle Components. They were very helpful when I visited and new the NG TF very well. Their knowledge of SVA requirements was also very good.
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The front lights are mounted in the fibreglass bowls. Rather than run the wires down through the wing and under the side panel as the manual suggests I bought some M12 stainless steel set screws to fasten the bowls to the cowl through the aluminium spacers. They were then drilled with an 8mm drill to take the cables into the cowl. The spacers were then drilled to 12mm to take the larger bolts. This is a neat solution and I am very pleased with it.
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The front indicators were fitted to the top of the front wing. The front of the the bolts used to hold them in place is also used for the wing strengthener. The wires were attached to this and went into the engine bay via small holes under the wing in the aluminium side panel.
The rear light pods needed cutting into the wings. There are various methods of fixing these to the wings but I chose to use the method in the build manual. I cut off the flange, taped a sheet of coarse sandpaper to the wing and by rubbing the edge of the pods up and down the wing I got the correct profile for the joint.
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Resin was then applied to the edge and the pod was "glued" in place. I then used a router (Don't forget to use the correct safety equipment as fibreglass dust off the router gets everywhere) with a roller guide to open up the wing from behind to the shape of the pods.
Some fibreglass matting was then applied to the inside of the pods onto the rear wings to provide added strength.
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The joint on the outside of the wings was then finished with some body filler to get a nice smooth profile. This took two applications to get it smooth enough.
I also fitted some side repeater indicator lights. These were fitted after the windscreen to ensure that they were in the correct place. They are designed for this steel so, because the fibreglass is thicker, they didn't fit well at first. I had to use small blobs of glue to fit them temporarily. The will be removed for painting and then more permanently fixed when rebuilding.
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Shortly after the SVA I purchased some driving lamps. I believe that these look good on this type of car and the Lucas ones I chose seem to suit the car well. They are smaller than the headlights and I think that makes them look better. There was an option to have a halogen coversion for £15.00 but at this stage I left that off. If they turn out not to be bright enough I will retro-fit them later. I drilled the holes throught the fibreglass and was expecting to have to make up a reinforcing bracket, however the fibreglass was quite thick and after consultation I felt that it was probably strong enough. Time will tell, but I can always reinforce later if needs be.
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I had already wired for the spotlights and removed the switch for the SVA. After connecting up the lights and reconnecting this switch I was pleased that they worked first time. They are wired through the beam switch so that they only come on with full beam.
There are also some side repeater indicator lights but these will be fitted after the windscreen has been fitted to ensure that I don't drill holes in the wrong places.
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Horns
Whilst there are many aftermarket horns available I opted for the standard MGB Hi note and Lo note. These were wired in parallel from a relay. By fitting a relay it also meant that the horns could be directly earthed to the chassis rather than have return wires back to the horn push button. The horn button only earths a low current circuit from the relay and earths through the steering column.
I made two right angle brackets to screw against the rear of the front cowl and into the front crossmember. These will be powder coated when the cowl is removed for painting. The horns were fastened to this.
The plan is at some stage to fit a klaxon type horn after the build is completed.
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Battery
The battery chosen was a Halfords HB053. It was slimmer than most others and fitted neatly in the recess in the body tub. A regular battery clamp was used to hold it in place. The diameter of the terminal pillars was smaller than standard and I needed a pair of collars before the cable terminals would fit. A red 110A 16mm cable was run through the tub to an isolator in the rear part of the cockpit, behind the passenger seat. From here it was run through the chassis holes to the starter motor. The Black earth cable went through the the recess towards the rear and fastened to the chassis earthing point. This point was also used as an earth for the rear lights.
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The isolator was fitted on the vertical face of the rear footwell on the passenger side. This means that I can reach it from the driver's seat. Having subsequently decided to build a boot the access is a little tighter but the isolator is even less obvious than before. There is an SVA requirement to have an isolation device and this works perfectly well.