Ford Prefect Hot Rod Wiring and other malarkey

Published on 24 November 2023 at 16:39

It all starts off looking like a proper mess but there comes a point where it all starts looking a lot better.

It was about at this stage that I thought it may be a good idea to add a separately fused accessory circuit. I realised I had forgotten a fuse for the fuel pump too o I attended to that while I was at it.

This end of things is pretty much finished now, a removable panel will cover it so that none of the wires are vulnerable. The thin brown wire at the top is just for the led's that will illuminate if a fuse blows. Nice little feature, that, saves any doubt as to whether the fuses are good or not.

The wires at the front of the car are for the electric fans, the headlight hi and lo beams, indicators and side lights. I added a connector so the flip front to which the lights will be mounted can easily be removed for access to the engine.

I am well in to the wiring on the hot rod now, I decided to make a loom from scratch so I don't have hundreds of unused wires etc. It's all quite simple if you take it one circuit or wire at a time, the 3 things that catch most people out are the hazard lights, the rear fog light and the windscreen wipers. The problems all come about because of the BIVA requirements eg the hazard lights have to come on when the ignition is switched off, the rear fog light has to come on with either hi or low beam but not side lights and the wipers must be 2 speed and have auto park. These problems sound like non problems to start with but then when you look in to them a bit more can appear confusing but once you understand the issues in depth the fixes are simple.

As far as the wipers and hazards are concerned the first and most important thing is to use the right switches - ie ones purpose made for the job. Durite make both, Lucas also make a couple of different wiper switches that do the business. You may be able to find a light switch that has separate contacts for a fog light, I couldn't and as so many cars these days are all CAN bus controlled the choice as far as used parts are concerned is a lot less than it used to be. Fortunately it's very easily solved with 2 diodes and a relay. One diode connects to the high beam switch, the other to the low beam with the other end of the diodes joined together so that either circuit being energised will supply 12 volts to the relay without powering the other circuit. You could take this straight to the fog light switch but you will get a 0.6 volt drop across the diodes. Using a relay avoids that, on my car the plus 12 going to the relay comes from a separately fused supply. All my light circuits are individually fused so that I should always have some lights even if I get a dead short and resultant blown fuse on one circuit.

The wiper is a bit of a different ball game as the way they hang together may not be clear at first look. The sort of wiper motor needed has to have a park switch - one of the traditional mechanical cam driven type. Mine comes from a Fiat something or other, I found it at a car boot sale. It looked very neat, it runs very quietly and I thought I had sussed out how to wire it. Turns out I was wrong because when I connected it up it worked for about 3 seconds then started smoking - I had misunderstood how the cam switch worked and hadn't realised one side of it was a permanent earth. Oh dear. Fortunately no serious damage was done, The contacts distorted with the heat but I was able to bend them back again. I need to change the internal wiring so it doesn't short out when it hits the park position.  I could have used one of the old mini units, it would have undoubtedly made the job easier and would have been compliant with the BIVA rules. If my tests tomorrow are unfavourable that's exactly what I will do.

The next thing is the hazard light switch, this is a lot easier as again special switches are readily available  for the job -  Durite do one, it's a bit big and clunky but they do work well and you can use a 2 pin flasher relay. My car retains the indicator switch on the column, the speedo will have the indicator warning lamps built in. You can get electronic flashers where you can adjust the flash rate for any given load, remember that for BIVA viewing angle requirements you will need side repeaters, which will take extra current and may change the rate of flashing, if you go with the variable type you can set it correctly once everything is in place.

The brakes are all done now, the steering is all hooked up and working splendidly, I know the engine runs so it's almost at the point of being driveable. Nowhere near finished but at least able to move under it's own power. My plan is to get all the mechanical and electrical bits finished, sort out an exhaust and then move on to the bodywork. It's going to have a stereo in it so the wiring is pretty much laid in for that, all the wiring will be well secured and hidden, I have seen some really nice cars ruined by a crappy electrical install, I don't want mine to be one of them.

Talking about the brakes I was gob smacked as to how easy it was to get them bled up, I expected to have a nightmare but it went far better than I feared. The brake pedal is rock hard and all 4 wheels seem to be firmly stopped when only light pressure is applied to the pedal. I will have to see how well they work in proper use - BIVA tests make sure the rears don't lock up first when emergency braking, it's impossible to tell if they will or not without a road test. If they do then a limiting valve will have to be fitted. I'm hoping that the massive tyres will have way more grip than the fronts so it hopefully won't be an issue. 

I guess the next thing will be to install the wiper assembly, work out the dash layout, install all the switches and then get on to the exhaust.

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