This is an article on the general uses of relays for (1) remote power switching (like air horn pump), (2) logic processing (like third brake light switching on a 1500 model), and (3) some common relay installations that may be a waste of time and money. The MGA 1500 originally has a pair of relays in a canned package for logic switching of turn signals and brake lights using common bulbs. I have posted a tech article on how to rebuilt that package (for about $10) when it goes bad.

The MGA originally has no relays for power switching (other than the mechanical voltage regulator). It's hard to justify use of power relays when the total power processing of the entire car is only 20 amps (aside from the starter motor). Lots of people think it may be appropriate to use a relay to off-load a switch contact (rather than fixing the switch) or to improve voltage to an end device by running a larger wire to be switch by the original wire (rather than installing the appropriate size wire or cleaning connector contacts).

I might mention some piezo buzzer uses. If you were to install a buzzer you might consider multi-tasking, or some additional uses for the same buzzer during the installation. In addition to lights-left-on warning, some states or local regions may now require lights to be on any time the car is in motion, or some members might prefer to use lights at all times for safety. The same buzzer might be equipped with logic to make noise if you start to drive with lights off.

If you were a little creative and so inclined, you could install a shunt resistor on any lighting fixture in the car that could supply current to trip a warning circuit if the bulb should burn out. You could install an oil level sensor in the engine sump to trip the buzzer or warning light if the oil runs low. Ditto for brake fluid, engine coolant, screen washer fluid, or motor fuel. These days you can install tire pressure sensors and an active warning device to let you know if the tires go low on pressure.

These may all sound like good ideas, and individually they may not be too complicated or too expensive to install. I have recently installed a 4-way flasher setup in my MGA (for about $10 net). I used to have a cruise control unit in the car, a few of them actually, but long since gone as a result of being more problem than benefit. I have an intermittent wiper module installed (because it was free to me on barter rather than $39 purchase). This device works okay but recently gave me pause to reconsider when it consumed additional time to remove and reinstall during the latest body restoration work (increased maintenance requirement).

At some point before people get to tinkering with various modifications and additions to their MGA, they should consider ramifications of possible future failures or maintenance requirements, and weigh the bothers against the benefits. I wrote an article once about installing driving lights, multi-fuse block and relays for driving lights and individual headlight circuits, nearly tripling the number of wire connections in the MGA in the process. That didn't strike me as any improvement in reliability (or safety).

One of the enduring charms of the MGA is that it is a simple machine with very few gadgets not required to make it go down the road, and therefore just about as reliable and low maintenance as it could possibly be. When you add a number of extra gadgets it is not just a matter of originality (or lack thereof) but is also running into added cost and time for installation of the gadgets, more time and possible cost of future maintenance, and increased probability of something going wrong with the car that might irritate you in the future.

Following is an abridged list of some things people occasionally ask about that fall directly under this call for consideration of bother vs. benefit (and practicality):

Dual line brake master cylinder.
Brake power booster.
Hydraulic fluid level sensor with warning light.
Front disk brake conversion for MGA 1500.
Any odd engine or gearbox conversion.
Cruise control.
Fuel injection.
Cross flow cylinder head.
Larger carburetors.
Modern audio equipment with amplifier and extra speakers.
Headlights in excess of 60-watt halogen upgrade.
High output halogen tail lights.
LED tail lights.
Electronic ignition.
High output ignition coil.
Electronic fuel pump.
Lights left on warning buzzer.
Four-way flashers.
Third brake light.
Intermittent wipers.
Three-point seat belts.
Roll bar.
Side impact door beams.
Crankshaft rear seal to eliminate a small drip.
Second battery after conversion to single 12-volt battery.
100-amp (or higher) alternator conversion.

Some people seem to have a fetish for spending money on the car after it has already been restored like new. It might start with some period accessories like chrome wire wheels, luggage rack, driving lights, badge bar, white wall tires and chrome wheel trim rings. Then what? If you still have excess time and money to throw at your pet car, then the sky is the limit. I may spend as much time convincing people that they shouldn't do this stuff as I do consulting on how to do it. How far can you go toward converting the 50-year-old car into a thoroughly modern machine before it dawns on you that it has become an unmanageable Frankenstein? Where should you draw the line in between? Maybe it would be better to train yourself to check the lighting switch when you remove the key. It was after all your choice to drive a 50-year-old car, so why not get used to living with its normal character rather than trying to change it into something else?