Fixing Common Electrical Problems

Michael Borg — 31 March 2015

If you run into trouble on the road, it’s handy to have couple tricks up your sleeve to get you back in the game. For now, let’s have a closer look at the basics of 12V fault-finding, along with a few convenient bush fixes.


Let’s say the fridge or your 12V lighting has stopped working...

  1. The first step would be to check that the fuse isn’t blown by ensuring there’s power at both contacts while the circuit is activated.
  2. If the fuse is okay, use a multimeter at the exposed positive wire closest to the accessory to make sure it’s receiving 12V. If the accessory is still not working, despite a 12V reading, you know there’s a problem with the accessory itself.
  3. If there’s no power at all, check the wiring between the accessory and the fuse.
  4. If there’s a relay in the circuit, check it’s working correctly by ensuring it has got 12V power at pin 87 (output) with the accessory turned on.
  5. If there’s no power, check the relay has constant power to pin 30, signal power to pin 85 and ground at pin 86. If all of this is present and there’s still no power to pin 87, the relay is busted.


Grab a multimeter and check the voltage at the alternator’s battery positive terminal is between 13.5V-14.5V with the engine running. If it’s not charging, for us 4WDers, it’s usually due to mud and ingress clogging the internal brushes of the alternator, so give it a thorough wash with clean water and see if it kicks back into life.


If your alternator is completely stuffed, it’s time to turn all of your accessories off so your battery keeps your engine running for longer. Remember, most camper trailers have batteries these days so you can swap it with your 4WD battery to get back on the road and, if you’ve got solar panels, it’s time to get them out.


Loose or corroded battery terminals are the leading causes of electrical problems out in the scrub. They can be responsible for things like the engine not starting, warning lights flickering on and off and even the cause of fires.


You can clean off corrosion by pouring boiling water over it. For loose battery terminals, you’ll need to shim the gap between the battery terminal and the clamp to get you out of trouble. One great little trick is to cut up an old Coke can and wrap it around the terminal before fitting the clamp back on. You could even wedge a self-tapping screw between the two.


A stuffed starter motor is bad news out on the tracks. Sure, you can usually clutch start a manual vehicle, but what if it’s an automatic? The first step is to diagnose what the problem is. For example, if the starter clicks when you try to start it, it’s usually either the battery is low, or the solenoid is sticking. If there’s no noise at all, you could have a wiring problem to the starter motor itself (wiring harness).


If the starter motor is clicking, the solenoid is likely to be stuck. Try tapping the solenoid with a metal rod (preferably with a soft end) while your mate tries starting the vehicle. It’s also common for the starter motor to get too hot, so let it cool down and try again a bit later.

If you’ve got no power to the starter motor and you can’t find the problem, you can use a set of jumper leads to bypass the original wiring by running the cable from the battery’s positive to the large positive terminal on the starter motor solenoid. Then, with the vehicle in neutral, use a wire or screwdriver blade to jump power from the solenoid’s main positive terminal to the smaller ignition positive terminal to actuate the solenoid until the vehicle starts. This is a last resort and should be avoided when possible, especially on modern vehicles.

Check out the full feature in issue #87 April 2015 of Camper Trailer Australia magazine.


12V fault finder electrical problems car issues on the road bush mechanic