The online Classic Community



How to check your electrical system, ignition system and fan belt


Problems with the electrical system are high in the top ten reasons for breaking down, modern cars have much more electronics and wiring and are therefore more complex so there is more to go wrong with them. On the other hand older cars and classics might have less complex systems but due to the age of the cars brittle wiring, corroded connectors or owner modifications these can all cause problems to these cars.
Most of these problems can be avoided with a little maintenance and checking.

Fan Belt

Fan and drive belts

With a slipping drive or fan belt the car will make a high pitched squealing noise when the car driven off. If the belt is not renewed or tightened then the alternator will not be charging properly so eventually you will run out of electricity and you will have difficulty starting the car.

Top Tips to avoid problems with the electrical system

1. Have the squealing fan belt tightened, it only takes a few minutes by slackening off the bolts on the alternator and pushing it away to take any slack in the belt before tightening the bolts back up.
2. This belt should be changed as per the service interval for your car but keep the old belt as a spare in car of an emergency.
3. A new belt will become slacker after wearing in so recheck for tightness after a few hundred miles.
4. When working on the belt the engine will be off but make sure you have the keys in your pocket, this way no one can start the car while your working on it.

Damp Ignition circuit

A lot of problems with the electrical system are caused by moisture. The ignition system is especially sensitive to it especially in winter and wet months. Spraying the leads, plugs and distributor cap with a water displacer like WD40 will help but it is only a short term fix and parts should be changed to permanently cure the problem.



Top Tips for ignition

1. With the ignition system on petrol engines being sensitive to moisture do not drive through deep puddles at speed as the water will get forced up into the engine bay and onto the electrics.
2. If the ignition cables (leads) are old and in poor condition the car will be harder to start, more prone to moisture or water attack and will probably make the car run rough until it is warmed up and moisture evaporates off. (sometimes you can see the sparks in the leads if you have the car in a dark garage)
3. When working on the ignition system (or any electrical system) disconnect the battery)
4. Clean the leads with penetrating oil (that does not contain graphite) but do not spray them with damp protector products (ones that coat the leads) as these coatings eventually crack and will then keep moisture in causing more problems.
5. If your leads, distributor cap or coil is getting on a bit then change them, the cost for a new set will be less than 50 pounds but the car will not only run better but there is much less chance of a breakdown..

Defective Wiring

Most modern cars have lots of electronics and sensors but a simple loose plug or broken wire can immobilize the car. The same can happen with older cars and brittle wiring or corroded connections can also render the car immobile. I had a problem with a Mini 1275GT where the low tension to the distributor wire had become work hardened with vibration and the wire snapped off just above the push on connector. Simply putting a new crimp terminal on fixed the problem (after first checking the condition of the Wire).

Top Tips for checking your wiring

1. The reliability of a car depends on the wiring, loose wires will chafe through and cause short circuits so make sure everything is tidy and taped up in the loom.
2. Add on circuits such as alarms, radios or telephones are sometimes installed carelessly and can cause problems with the existing wiring especially if the original loom has been taped into to get power connections etc.
3. Check the fuse box and make sure all the wires which come and go from it are neat and tidy with good connections to the fuses.
4. Ensure that the fuses are all the correct type and size in the fuse box (fitting a larger fuse in a circuit can cause fires).
5. If new accessories are added make sure that they are fused and that the correct gauge of wire is used with a relay if necessary.
6. If the wiring on your classic is brittle and snaps easily then it might be a good idea to re-wire the car, new looms are available for most classics and do not cost a fortune.