Some Useful Tips For Simple Fault Finding On Cars.

1) Car Starter Motor Drags.

Although this can be caused by a faulty starter motor or battery, some times it can be a simple thing such as a corroded battery terminal or poor connections on the earth wire or positive wires to the solenoid and starter motor.

A useful tip to use if the vehicle is at standstill and cold, and the starter motor drags is to feel the connections with your finger at the battery terminals, earth cable, and lugs at starter motor. If it is a loose connection it will cause a tremendous amount of heat and it will be fairly warm to the touch.

Switch the head lights on. If the lights are very dull suspect your battery.

If the lights are on and bright crank the starter motor. If the lights dim completely suspect a faulty stater motor or tight engine.

2)  Starter Motor Spins Freely Without Engaging.

It might possibly be that your key switch has a high resistance. For a test you can take 12 Volts from the battery straight to the terminal on the solenoid that is fed from the key switch. If the starter motor engages correctly your key switch is faulty.

 You can fit a new key switch. A cheaper option is to fit a relay as shown below. Any hooter or  relay will work. It is a lot cheaper and easier than replacing the key switch.

Ensure that you use no less than 2.5mm square wire on the contact circuit. The thicker the better. Insert a 20 amp fuse into the inline fuse holder.

Tail Lights are dim, and flash with indicators.

This is normally a sign of a corroded earth connection. Check earth connection and clean if necessary. If you cant find out where they earthed it from, trace the earth wire from the tail light and fit a new wire and lug to form an earthing point.

Simple Headlights On Alarm Circuit.

Although this is not problem solving I thought I would just add this in. All you need is a 12v Piezo Sounder which you can obtain from any electronic shop as shown below. It must have its own internal oscillator circuit.

You will also need an inline fuse holder with a 1 amp fuse and reed switch as used in burglar alarms and wire.

Reed Switch which is operated by magnetic field

Inline Fuse

Some Heat Shrink Sleeving

 Instructions

1. Take a wire from the negative terminal of the sounder and earth it to the body.
2. Take a wire from the positive wire and route it carefully to the headlight. Leave a bit extra. 
3. Slip the correct size heat shrink over the wire in the head lamp side. It must be 30mm longer than the reed switch and be able to slip over the reed switch.
4. solder the wire that you routed onto any side of the reed switch.
5. Take another piece of wire and solder it on the opposite side of the reed switch. It must be long enough to reach the positive terminal of the battery.
6. Slip the heat shrink sleeving over the read switch. Heat up with a hot air gun or lighter to shrink sleeving.
7. Carefully remove some of the tape around the loom at the headlight. Find the earth wire that comes from the head lamp. Wrap this around the reed switch about 6 times. Do not cut the insulation of the earthwire.
8. Tape the loom closed with the reed switch inside.
9. Slip a piece of heat shrink wire over the opposite end of the wire. Strip wire and solder to inline fuse holder. Slip heat shrink sleeve over join and shrink with heat.
10. Fit lug on opposite side of fuse holder to match bolt on positive terminal of battery.
11. Disconnect the negative terminal of the battery.
12. Remove the nut from the positive terminal and slip the lug onto the bolt and tighten.
13. Refit the negative terminal.

How it works!

The reed switch is operated the moment a magnetic field is nearby. By wrapping the wire around the reed switch you are forming an electric magnet. The negative wire (or common) is used to make sure that the alarm is triggered irrespective of if the bright or dim lamps are left on.