How To Diagnose the Ignition System of a Truck Easily

Do you want to learn how to diagnose the ignition system of a truck? The ignition system is the part of your truck that you should inspect whenever you perform general truck maintenance. Checking it does not consume much time and saves you from frequent breakdowns. 

How To Diagnose the Ignition System of a Truck

This guide will detail how to diagnose the ignition system of a truck, which is otherwise similar in many other vehicles.

The ignition has low-tension connections. Consider checking if they are tight and are not corroded. You should also check if all the low-tension wires are well insulated and if no cracks have formed on them.

Check The Leads

Check if the leads are clean, dry, and crack-free. If your truck has special guide clips, check if the leads are running inside them. The clips play the role of protecting the leads.

If the leads are dirty, use a soft cloth to clean them. If they are not in good working condition, consider replacing them. It would help if you replaced the high-tension leads every three years. Doing this will help in maintaining the peak performance of your truck.

Check if the spark plugs are well fixed on the leads and if the leads are well connected to the distributor. When doing this, have sticky tape to make tagging, so you do not mix up the connections.

The threaded collars are used in screwing the leads vertically into the distributor and are held by crimped terminals or tiny screws.

Check if there are cracks on the distributor and the plug caps. You will have to pull off the plug caps one after another to do this. Pulling one after another will protect the lead from damage. Wipe the tops of the porcelain plugs.

Remove The Distributor Cap

It may have spring clips or two small screws. When removing the distributor cap, do not drop the spring clips or the screws. Inspect if there is any crack inside the cap. Check if the sprung carbon brush at the top can slide freely up and down. There is a spring contact on top of the rotor arm. Check if this spring is free from damage or wear. You might find the roto-arm tip dirty. All you need to do is to lift off the arm and clean it by scraping. Scrapping will also remove corrosion around the rotor-arm tip.

Narrow pipes run from the distributor to the inlet manifold. If you have an older truck, these pipes will be metallic. Most of these pipes are plastic which is a push-on fit. Inspect and check the physical conditions of these pipes.

Check the Coil

The standard type has a thick HT lead flanked by two smaller LT leads. Check if the lead is correctly fixed to the coil and distributor, and ensure that the rubber seals are well fixed. Ensure that the coil is fixed adequately on its mountings.

You will see two leads from the switch to the coil, one going through the resistor while the other bypasses the resistor and provides an additional ignition strength. 


The ignition system has various parts. To diagnose the ignition system, it requires one to have prior mechanical mastry. If you haven’t done it before, consider the services of your mechanic. 

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