So - I've had some issues with my dash lights - they do not illuminate when the switch is on. I started another thread on this, but now have move to a new thread because the issue has become an electrical question.

Symptom - no dash lights when headlights "on"

There is an issue with fuse 25E. This fuse is a 10amp and runs the interior dash lights via the headlight switch. I found a blown fuse. I replaced the fuse with another 10a, and immediately it blew. This was with the engine off/no key in ignition. I tried a 15a and same thing. Then I tried a 20a and there wasn't an issue. However, when I was out in the evening, it went. So I know there is an issue with the circuit.

I've looked at the wiring diagram but am having a hard time deciphering what I should be looking for. Also, how should I be testing this?

Questions:

1) why is this blowing the fuse while the engine isn't running? What does that indicate.
2) What is the main cause for this fuse to blow
3) Where should I be looking for an issue? Between the fuse box and the switch?



Here's the wiring diagram:

 

I would really not recommend increases fuse sizes like that. As I bet you do know. But you can take out an entire ECU by doing that.

1 - The dash still gets power with the engine off, just like the interior lights or entertainment systems stay online longer. But this could also indicate physical wire damage.
2 - If we knew, you would not be posting. You could remove the dash cluster and see if the fuse still blows. I dont think it will, but if it does it could point to a wiring issue versus the cluster itself. But I consider this a long shot at best.
3 - I would try a different switch first. They have been known to fail. But get a used one maybe, dont want to waste $$ incase the switch is not the issue. But.....without the dash writing diagram handy, the switch may just be telling the central junction box to turn the cluster lights on. If that is the case, the switch itself may not be the issue. Also you may be able to remove the switch and use jumpers to power on each system one by one that the switch would normally turn on? Never tired that myself, just a thought.

So I guess my first thought would be to remove the cluster and see what happens to the fuse. Like I said, probably won't blow. But if it does then you have really narrowed things down and my money would go on wiring or some issue with the CJB.

 

Did some searching... One forum suggested: "...resolved the issue by fixing contact #9 in the connector on the back of the light switch."

 

Connector 9/ connector behind the plug was fixed and it was a loose connection begin with. I could wiggle it and the lights clicked on then off. So I had looked at that as a cause. Seemed all well and good but then the fuse blew. All of sudden it wasn’t just the connector.

Someone mentioned to me that it could be grounding itself as opposed to being open - not sure if that is a cause.

yes - I know that the fuse amp increase was
risky. I won’t put a higher one in until resolved.

if I read the wiring diagram right, I should be looking for a brown/ green into the switch?

 

Also - I think I meant when I posed question 2…

in general what causes fuses to blow? Drawing too much power I assume. This is correct ? And if that’s the case, what would cause a circuit to draw more amps than it was designed?

 

I'd say the most common causes for a fuse blowing is a short to ground. The short pulls more current than the circuit is designed for and blows the fuse, which protects the wiring and connected components.

 

So let me ask this.

how best can I isolate this type of fault?

and

based on the wiring diagram, could this be rewired from the engine fuse block?

I don’t understand the connection shorthand on the diagrams- there is a connector somewhere?

 

Best advice I can give if you're new to this is to search for Scanner Danner on youTube and watch some of his videos on basic electrical testing and understanding automotive wiring diagrams.

For the basic test for a short all you need is a simple test light though - hook it up to battery positive, touch what should be the positive wire in the circuit and if it lights up, that wire is grounded, i.e. it's shorted to ground when it shouldn't be.

Just make sure you don't fry any components by applying power with the test light where power shouldn't be.
Best advice I can give if you're new to this is to search for Scanner Danner on youTube and watch some of his videos on basic electrical testing and understanding automotive wiring diagrams.

For the basic test for a short all you need is a simple test light though - hook it up to battery positive, touch what should be the positive wire in the circuit and if it lights up, that wire is grounded, i.e. it's shorted to ground when it shouldn't be.

Just make sure you don't fry any components by applying power with the test light where power shouldn't be.

If you find a shorted wire, it's a proces of working backwards to isolate the area where the short is happening. Visual inspection is key here, looking for failing insulation where the wire conductors are making contact with metal or another wire.

So wiring can cause a short, but components can also be shorted internally - in this case you could have a bulb thats shorted itself out or an issue with a connector or a relay etc

 

Update on this.

I replaced the switch. Partial success.

I now have no issues with the blown fuse. However I still have no dash lights.

:/

any ideas on this ??

 

Do the dash lights work at all now? Is it still a case of them turning off when you turn headlights/parking lights on?

And by 'dash lights', do you mean the entire instrument cluster? Is that right? Just want to make sure exactly what you mean.