Electrical Gremlin

OK guys, this will be a hard one for you techies out there.

On Saturday I drove around all morning, started and stopped the Nav about 5 times. Then after getting back in the car after getting lunch (turned off for about 10 min), I turned the key to start and all the dash lights went out as if the battery was disconnected. I turned it off and then went to start it again, it would not start but made a bit of a clicking noise like a solenoid ticking. I thought OK, flat battery so I tried with a jump pack and all I could get was a very slow cranking over of the motor, but not enough to start. So on the phone to RACV. The guy try's to start it and now nothing at all not even dash lights come on, so he try's to jump start it and still nothing, he tests the battery and it comes back fine. Then he starts poking around with a test light and finds that there was no power at the ignition barrel and no power anywhere in the fuse panel under the dash. He then just called a tray truck and I had it towed to my mechanic.

I get a call from the mechanic this morning and he says that he put the key in and it started straight away no issue at all. WTF!!!!!!!!!
He is going to take it to an auto elec and see if they can find anything, but the problem is it is hard to find anything wrong when it is working fine now.


Any help would be great.

It sounded like there was a battery connection fault there for a minute.

Highly corroded battery terminals - or terminals that have broken away from the plate inside the battery - could provide "erratic" power. A corroded earth strap would do this too, even though "positive power" disappeared from the ignition, what you're measuring is the circuit from there back to the battery and if the earth strap is gone, or corroded, you have no circuit to measure.

Putting a jumper pack across the battery doesn't fix a corroded (or loose, I suppose) earth strap, but does sorta say that it's not something inside the battery. You get variations in supplied power because of movement.

That's my guess anyway.

The thing is, it did not do anything when I left it at the mechanics yard on Saturday arvo as he was there and he turned the key 5 or 10 times and there was nothing at all. It just sat there till this morning without moving at all and then it started 1st time today. I will check the earth strap and see if that's OK, It may be a bit mudie, but that's about it. The battery looks fine no corrosion at all, it is quite clean and has some of that blue insulating stuff on the outside of the terminals to stop it shorting, but that was put on after the terminal cables where connected.

try checking the ground to the body from the battery. last time something similar happened to my nav a quick clean on the body where the ground terminal from the battery connects to sorted the problem.

I would say battery connection.

Dave.

Auto elec replaced the - battery terminal and some special fuse thing under the dash somewhere. hopefully that fixes it.

My other thought would of been a fusible link.

Dave.

Dave said:

My other thought would of been a fusible link.

Dave.

Click to expand...

That sounds familiar. What is it???

Its a bit of wire that in normal conditions just tramsmits electricity through it but if it gets a power surge it will burn out.

Dave.

It's a great big flat piece of metal between two poles with a clear window that looks in on it so you can see if it's blown. It'll be stamped "140A" or something like that.

AKA big arse fuse.

Isn't it under the bonnet though not under the dash?

Might have moved it under the dash from QD32 to ZD30 I suppose

Cool, I didnt get much of a chance to speak to the mechanic about it as they where busy and packing up for the day. I assumed it was some sort of fuse thingy.


Thanks for all the help guys

My D40 has them in a few places. There are a couple bolted to the battery terminal as well.

Old.Tony said:

My D40 has them in a few places. There are a couple bolted to the battery terminal as well.

Click to expand...

That's intense. I'll stick to my QD32 then

Well it looks like the battery terminal and the fusible link that was replaced a few weeks ago was not what the problem was.
I came out of work on Friday night and the same problem happened again, turn key to on and then start and all the dash go's blank. Then when key is turned to start there is a clicking noise from the fuse box area under the bonnet and all the dash lights flicker.
So RACV turns up and attempts to jump start with no luck then decides to call a tray truck, while waiting for the truck I was listening to the radio (it was working fine) I then put my foot on the brake and the radio stopped and the interior light went out (it's LED). Then there was no power at all after that, I couldn't get any lights on the dash, the interior light would come on but only very very dim, and now for the strangest part,
with the key turned off and taken out of the ignition the radio would light up, it was very dim but it was defiantly lighting up and flickering. I could not turn it on or off and it didn't matter where the key was the radio wouldn't change. When I turned on the headlights on (they didn't come on) the radio would go off, but when lights turned off the radio would light up a little bit again.

Any ideas guys???

Initial guess is an earth, but will add an observation about my own vehicle first.

In my car, if I have the ignition key in my pocket, when I press the brake pedal and activate the trailer brakes with the brake controller, the car's instrument cluster comes to life as if I've turned on the key AND it's possible to raise and lower the electric windows. I think it's wrong, it needs to be fixed, but there it is.

There is some relationship between the brake pedal/brake wiring and the ECU. There's a good chance that the guys that hooked up my brake controller spliced into the wrong line behind the dash and when activating the brake controller, the power that is fed through from pressing the brake also backfeeds through the brake controller and into the ECU, firing it up.

Finding THAT gremlin probably won't be too bad, because it'll very likely be one of the connections off the brake controller.

I wonder though, in your case, if the earth that's shared between radio and instrument cluster (and now possibly your Uniden radio) may be at issue? What happens if you are experiencing this gremlin and you turn on your UHF radio?

I'm not sure where the ECU is earthed, but if that earth point is affected, you can give it all the positive connections you like, it needs to be connected to negative as well to get the voltage to start properly. Same for the other modules like the BCM that controls interior lights, mirrors etc. There'd be a LOT of value in connecting a jumper lead to the battery negative, running that into the cabin, and with the dash apart, testing the resistance between every ground connection and that lead. It should read very, very close to zero. If not, there's your problem - a bad earth!

Finding it may not be easy, because it could be the earth point in the engine bay, or the connection between the instrument cluster and radio, or a dozen other places. I'd concentrate around where changes were made - like the sound system, UHF etc first. You could test these while you have that heavy cable in there - hook up the radio's earth to the jumper lead negative and see if the gremlin's gone. You can't damage anything, because the thing is already supposed to be connected that way.

Old.Tony said:

In my car, if I have the ignition key in my pocket, when I press the brake pedal and activate the trailer brakes with the brake controller, the car's instrument cluster comes to life as if I've turned on the key AND it's possible to raise and lower the electric windows. I think it's wrong, it needs to be fixed, but there it is.

Click to expand...

We had the opposite situation in a Pardo about 6 months back. The Prado comes with push button start so as long as the key fob is in the car the engine will start and there will be power but the guy who hooked up the brake controller stuffed up, wired it wrong and every time there was power to the controller it blew fuses under the dash and left no power in the switches and cluster. We re-wired it in the end because we needed to put the cattle trailer on the back but once again it goes to show how well some people do their jobs.

From my experience, it still sounds like a dodgey battery, or a bad earth.

Also check the battery connection to the starter. A poor connection there can cause weird things to happen to.

All sorted guys. Thanks for the help. It turned out to be an internal fault with a kill switch that has been installed on the bull bar, it is like a big battery switch thing that is connected to the earth cable, it has been seized in possition ever since I got the car, I actually broke the knob part off the switch attempting to get it to turn. That's why I never even thought it would be an issue. But the auto elec had a look and said that it was shorting out internally and is stuffed so he has just bypassed the switch and joined the 2 earth leads together and hay presto it all works fine again.

Good work, hope its smooth sailing from now.

Dave.