Check that all connections are clean and tight. Clean the connections if necessary, and smear the battery
jelly - not grease.
Ensure that the battery is fully charged and that the
is above the
. Test it with a
should be well above 1.230.
For a less accurate check,
and watch them while a helper works the
. They should dim only a little, and the starter should turn at its usual speed.
If the lights dim badly while the starter turns slowly, either the battery is low or its connections are unsound. Re-check its connections, including the
earthing strap (See
Checking battery leads and connections
); if necessary
For further tests you need a
- although you can make a rough check with a test lamp and leads.
Instructions here are for the more common negative-earth system: with a positive-earth car read - for + and + for - throughout.
A ballast-resistor system
The voltage reaching the coil may be 12
, or about 7 volts if the coil has a
Most electrical equipment works on 12 volts, but most modern cars have a
to assist starting.
The coil in a ballast-resistor system is rated at 7-8 volts instead of 12 volts. When the
is operating, the coil is fed with 12 volts from the starter.
produces a very large HT
for the sparkplugs at the critical starting time.
has started, the coil is fed in the usual way from the
switch. To stop the coil from burning out, the 12 volts from the switch is usually passed through a resistor block (mounted on or near the coil), which reduces the voltage.
Some cars have, instead, a special high-resistance wire between the ignition switch and the coil to reduce the voltage.
Checking the voltage
Make sure all connections are clean and tight. To check that voltage is reaching the coil, connect the voltmeter between the + or SW terminal of the coil and earth, and switch on the ignition.
should read nearly 12 volts, or about 7 volts if the coil has a ballast resistor.
If there is no voltage, there is a break in the circuit between the battery and the + terminal. Possibly the ballast resistor is faulty.
Checking the coil
If the previous test shows no fault, test the primary winding of the coil.
the contact-breaker points open with a piece of plastic or card.
Connect the meter between the or CB terminal of the coil and earth, and switch on the ignition. Again the meter should read about 12 volts.
If it reads zero there may be a break inside the coil winding, or a
to earth inside the
or in the LT lead.
Check further by disconnecting this LT lead and repeating the test. If the reading is zero, and the ballast resistor is sound, the coil is broken and should be replaced.
If the reading rises to about 12 volts, the distributor or its LT lead may be short circuited to earth.
Checking distributor leads
Check that the lead looks sound and the connection is clean and secure; check in the same way the short wires between the distributor LT terminal and the contact-breaker terminal post, and between the points and the
Look at the condenser itself, which might perhaps be short circuited to earth. Remove it from its mounting and check the voltmeter reading. If it is correct, the condenser is faulty; renew it.
Close the points. Leave the meter connected between the - or CB terminal of the coil and earth. Switch on the ignition. The reading should be zero.
Any voltage, even a very low one, may be caused by one or more faults, such as, dirty or oily points; wrongly set points not closing properly; points of the wrong type for the distributor; a bad earth connection between the contact-breaker baseplate - or the whole distributor - and the engine.
Other faults possible
Other causes can be a previously unnoticed break in the lead between the distributor LT terminal and the contact-breaker post, or even in the LT lead from coil to distributor.
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Bosch distributors are found on many different cars and are generally very
reliable. But after a high mileage you may find that the engine isn't running
quite as it should. If the rest of the fuel and ignition system is well tuned
but the car doesn't accelerate cleanly, the problem may lie in the distributor
The high-tension (HT) or secondary circuit carries high-voltage electricity. It runs from the secondary winding of the coil through the distributor to the plugs. Any of these can break down and cause ignition failure.