Short all of a sudden., Short circuit Options

[John90290]

Been chasing this all day. So frustrating. Took the car out for a spin and noted the fuel gauge wasn’t working and the rpm gauge was off slash not working and the “gen” light came on. Got to Home Depot and saw a blown fuse. No problem. Easy fix bc I carry spares. Got back in and it blows. Now what really blows... I’ve been bird dogging this all day. Pulled the tail lights to check for a short. Nothing. Wipers work ( before fuse blows) and wires to motor look good. Not sure what could be causing this and wondering if it could be the fuel sender? It’s under the evaporator tank (1975) so don’t feel motivated to take the 12 bolts out to get to it. It is an after market sender.

Could there be a problem or short in the gauges or is this the wrong fuse?


Wondering if any of you folks have run into this and have a place to start?

Thanks!!

[ejm]

Highly unlikely it's the fuel sending unit which doesn't see direct power and only provides ground paths for the gauge and low fuel warning light.

I would start by checking that the brake, turn and backup lights are all working correctly and then inspect wiring around the brake and backup light switches.

[Mike Bellis]

Brake light wire under the toe board, at the pedals.

[John90290]

Brake light wire under the toe board, at the pedals.

Thanks for the guidance. Three more hours and I have the short nailed to the brown yellow or brown white ( can’t telll) wire coming out of the back of the brake light switch. With that disconnected (cut) all is right with the world. My wiring diagram does not have that wire? What is it for? Is the switch bad?

[lierofox]

The wire colors for the brake light switch should be:
Black with Yellow tracer: Brake Lights
Red with White tracer: Goes to the voltmeter, and oil temp gauge
Gray with Brown tracer: Goes to the reverse lights.

Check to see if your reverse lights work because that looks like it's the Gray with Brown tracer wire. That wire goes back to the engine bay relay plate on the 14 pin connector, it then exits the 12 pin connector and goes to the transmission reverse switch before looping back into the 12 pin connector, back out the 14 pin connector, and finally goes to the reverse lights.

I've never actually driven mine with the stock Type IV engine, but I believe that wire passes through the engine tin at the same spot where the starter wire passes through, on its way to the reverse switch. Might be a good spot to check for chafing.

[theer]

(IMG:style_emoticons/default/agree.gif)

The reverse light circuit provides power (not ground) to the lights through the switch at the transmission, so if the feed wire pops out of the switch it can short against the trans and blow the fuse.

And yes, I figured that out the hard way!

[Rand]

Brake light wire under the toe board, at the pedals.

Bellis FTW (IMG:style_emoticons/default/smilie_pokal.gif) (IMG:style_emoticons/default/biggrin.gif)

[John90290]

Well... pulled the 12 pin to check for corrosion and found some.

[lierofox]

Oh no! I know it goes without saying and it's nothing but too-little-too-late at this point, but always make sure to unplug the battery when working on electrical stuff!

Basic automotive electrical mathematics:

Red + Black = FIRE!

(Or in our case: Black + Brown = Frown (IMG:style_emoticons/default/sad.gif) )

[John90290]

Oh no! I know it goes without saying and it's nothing but too-little-too-late at this point, but always make sure to unplug the battery when working on electrical stuff!

Basic automotive electrical mathematics:

Red + Black = FIRE!

(Or in our case: Black + Brown = Frown (IMG:style_emoticons/default/sad.gif) )

Agreed and I always do. In have a quick disconnect mounted permanently on the car and reconnected to see if reverse lights worked then smoke. By the time I walked back to battery to shut it down it was a smoke show (IMG:style_emoticons/default/sad.gif)

[Tom]

John90290,
You should do it the old fashioned way ( disconnecting the battery - negative cable!). When you hook it back up you can see an arc and quickly remove the cable before too much damage is done. In your case the switch would need to be on as you re-connect the negative battery cable.
Be careful removing or re-installing that 14 pin connector. It has two large red wires that come directly from the battery, not fused either. Placing the connector back on one pin off and having not disconnected the battery has ruined several 914 owner's day.
Tom

[Olympic 914]

Well... pulled the 12 pin to check for corrosion and put it in one row off. Nearly Set the car on fire!! Fried the purple black wire from the coil to the 12 pin connector and I mean fried bare wire the entire run.

You are not the first to do this.

Don't ask how I know.