Red-Blue wire grounding? Need help with routing.

[Naamiokostaja]

Hi all,

 

My first post on this forum... I recently purchased my dream car, a -70 240Z, US import. Very happy with it, but recently I noticed no lights on the gauges and the internal lights would not turn on. Checked the fuse box ( it's the MSA? more modern box ) and found the blown fuse. As I try to replace it, it burn instantly. Checked with meter and seems red(blue) wire is grounding. Now as I start to search for the wire that might be grounding, I was hoping someone could help explain where it's routed through? 

 

I would assume it comes from behind the center console, somewhere visits the gauges? continues behind the glove box, on the floor next to the door and up the passenger side column. Then on the ceiling to the ceiling lamp. Did I get it right? It's just that seems a bit of a daunting task hunting for the wire. 

 

It's the gauges with out light, otherwise work fine, then ceiling lamp, map light, glove box light that are out. At least have not noticed anything else. 

 

All support appreciated. 

[NewZed]

Here's a diagram showing some red-blue wires.  A few things to check, like the reverse switch (it's surprising how unprotected and dirty that area is on the transmission.  Seems like more shorts would happen there), inhibitor switch, blower motor, etc.

 

http://www.atlanticz.ca/zclub/techtips/wiringdiagrams/240z/1970_240z.gif

[Naamiokostaja]

Great! Thanks NewZed. I would thus assume I'm looking for that switch being then shorting. Remove wires, check with meter? The blower motor seems to be working fine. 

 

To make sure I'm looking at the right thing, if there would be an issue, my reverse light would NOT come on if there is an issue. 

The reason I'm asking is, that as I read the chart, it's a red - red/black going to that switch. 

 

Currently (what I've noticed is) Gauge lights not working (gauges work just fine) Dome light not working, map light not working and glove box light not working. Everything else seems to be working just fine. Cannot be sure about the rear window defrost as the contacts are corroded, never tried that one yet.

Edited September 15, 2015 by Naamiokostaja

[NewZed]

You're looking for a wire that comes from the fuse that is shorted directly to ground.  That's what would cause a fuse to blow immediately.  So, for example, on the reverse light the wire to the switch has power.  When you put the lever in reverse the switch completes the circuit and the power travels through the switch to the reverse lamp and then to ground.  If the power supply wire got pinched and shorted the power would have no resistance from the reverse light and would blow the fuse.

 

That's just one example.  Each load - the light, the blower motor, the relays - has a short section of wire with power.  Many of the loads are actuated by grounding the end of the circuit with a switch (like the brake lights), rather than providing power at the beginning.  Those are where the problems come from.  A short circuit across a lamp socket (the electrodes touch at the base of the bulb) is a common problem that blows fuses.  Even the loads that have a switch providing power at the beginning of the circuit still have a short section of wire with power, to the switch itself.

 

On your car, the diagram seems to show that power runs through the inhibitor relay to the ignition switch then a fuse on its way to the reverse lights.  But it's an odd format and I can't really tell what it's showing, if the fuse is inline or at the fusebox.  You might try disconnecting things, like the ignition switch, or the combination switch, until you can get the fuse installed.  At least you'll narrow it down to a smaller area.

 

Edit - forgot to say:  your fuse box cover should show which circuit that fuse is for.  That would be an important clue.

Edited September 15, 2015 by NewZed

[Naamiokostaja]

Thank you for your patience NewZed. 

 

The Fusebox indeed does point to Domelamp, Intrument panel and ? Luz? 

 

I assume it might be bypassing the ignition as the circuit is powered even though the ignition keys are not in.

 

I'll wait for the weather to get worse so I'll put the car in winter storage, should give me the time then to start backtracking wires and pull panels.