Warning Lights and Instruments
Instruments and warning lights are similar to switch gear in that they have a huge impact on the finished ‘look’ of the vehicle. Once again the choice varies from second hand to new and depends on budget, styles available and the type of look you are after. Aftermarket instruments will come with instructions and wiring diagrams, liberated ones you will have to figure out - go and visit the library again.
Before you leap into buying instruments from any source consider what you will be using the car for and what information you want or need. Is oil pressure better served by a gauge or warning light? Do you need to worry about boost pressure in a turbo or supercharged car? Is fuel pressure or oil temperature an issue? Do you want a rev counter that tells you the maximum revs you reached? You may well find that the features you want start to limit the choices available to you. Once you have selected the types of instruments there are considerations such as size, colour and number of instruments (some styles feature two gauges in one housing), and metric or imperial scales. If you want to be able to control the instrument illumination you will need a dimmer as well.
You must buy the correct senders to match the instruments as adapting orphan parts to fit and work correctly can get expensive. Instruments removed from wrecked cars should include plugs as well. Also ensure your rev counter is compatible with your ignition system. A good instrument service can sort this all out for you - at a cost. It will probably save you money if you can get the speedo cable (both inner and outer) from both the car your gearbox is from and the car your speedo is from so they can be joined together.
Calibration of speedo for both distance covered and speed will be required unless you work from a complete donor car or don’t care what your speedo reads. If you intend to race your car or drive it hard getting the rev counter calibrated may save you over-revving the engine without realising it due to an inaccurate instrument. Most instruments require a stabilised voltage so make sure you have a stabiliser connected. Additionally things like brake fluid level warning lights are fed from this stabilised voltage also.
With warning lights you need to realise that some (like alternator warning lights) need diodes to limit the current flow to one way only. Also it pays to have the seat and steering wheel in place (or at least have the normal driving position mocked up) so that you can locate everything where you will be able to see it. An instrument or gauge you can’t see with your hands on the steering wheel in a normal field of vision isn’t really worth having!
If you run a low oil pressure cut out then you probably don’t need a warning light as well - over to you. I don’t like having only an oil gauge as I once had an engine pump all the oil out through a leak and seize - how often do you scan gauges when driving fast on twisty road or when you are in heavy traffic? At least a warning light is a little more attention grabbing. My brother in law’s rally car had a turn signal light (ie 50 mm diameter) serving as the oil warning light that was also attached to a buzzer...no way you could miss that one!
You can get high pressure oil pressure switches that will set the light off at say 15 PSI as opposed to normal ones at 5 PSI. These are not a good idea if you have an oil pressure cut out - I found that once the oil got hot it thinned out (even using full synthetic and an oil cooler) to the point that the starter motor couldn’t turn the engine fast enough to build up sufficient oil pressure to overcome the cut out! The easy fix was to pop the wire off the oil pressure switch - back to instant starting, which is also handy on an EFI car if the battery is a little flat.
