1972 240z - No power when key turned, need some help fixing it properly

[240z8]

I picked up a 1972 240z a couple days ago and have had a bad time working with the wiring. The harness that plugs into the dash wiring, then goes to the back of the car for all the lights, was 90% chewed through by field mice. My friends and I have about 20 hours into cleaning up the wiring so far. We tried replacing the ignition switch, the voltage regulator, the fuse box and the accessory relay to try to get electricity into the dash with no avail, so we started cleaning. Plugs and terminals of any sort under the dash that we could reach were sanded, given a little dielectric grease and reconnected. Nothing happened. We break out the multimeters and the Chilton's manual and start tracing wires. We found out the large gauge W/R wire feeds power to basically everything I'm trying to figure out now and started making sure it didn't have a short anywhere. With all good fuses, we got a reading from each point that it connected from the alternator to the ignition switch. After pulling the dash out a little and examining the wiring harness further, we didn't find a single spot where the wires had been chewed through. The glovebox light wires were taped up out of the way and we found three wires just going to NOTHING. On the section of harness that goes from the passenger side, over the glovebox, and to the fuse box, there is a W/B wire, a BLUE/W wire, and a W wire. The W and W/B wire, I believe, are part of the turn signals, hazards, and brake lights and the BLUE/W wire is part of the wiper motor's electrical system. After finding all that and realizing we had gotten sidetracked with stuff we should be doing later, we went back to the "no power to the ignition switch" issue. I replaced the fusible links going from the starter to the large WHITE wire in the engine bay harness and the fusible link from the alternator to the large WHITE/RED wire which, again, changed nothing. Then I got the bright idea to run a 12v line from the battery to the W/R line right where it enters the passenger-side firewall. Unplug the connector, attach the hot wire, turn the key, and BAM! EVERYTHING WORKS! Not everything, just the stuff we were trying to figure out for two days straight haha. We spray some ether in the carbs and get a gas can with a couple hoses ready, and the car that has been sitting in a field, with mice living in it, sand burying the front crossmember, and wiring being chewed up for 14 YEARS started on the first try! 

 

I'm not leaving my wiring rigged like that; I just need help understanding the power circuit throughout the car. How does power go from the battery, to the starter, to the rest of the car? Where does the large gauge WHITE wire make a connection with the WHITE/RED wire to power the dash assembly? My first total guess was "Maybe it goes through the ammeter!", which is why we pulled the dash in the first place, but looking at the diagram further, it looks like the large WHITE wire splits off towards the front of the car, from the starter, to the voltage regulator, then out of the voltage regulator, to the alternator, out the alternator, through the fusible link I replaced, and into the WHITE/RED wire. Do I have that correct or am I just making wild guesses here? Is it possible that I have a short somewhere in the engine compartment between those components? If the voltage regulator is malfunctioning, can it keep power from getting back inside the car? Do I have the concept of that all backwards? I've found a lot of good stuff on this section of the forum that's gotten me this far, but I can't find what I'm looking for exactly.  Any input is appreciated.

[Six_Shooter]

There should be a white wire coming off the starter, that feeds into the harness running next to it, which in turn feeds into the car.

 

According to the FSM, this wire splits off to the fuse box and to the ammeter. The ammeter then feeds the ignition switch and other parts of the fuse box. You can bypass the ammeter by connecting the large white and large whit red at the ammeter together, if you think the gauge itself is a problem. You can also test that there is 12V on both of these wires with a DMM as a better way to troubleshoot.

[240z8]

Alrighty, that narrowed everything down significantly. I may have been complicating this problem a little too much it seems haha. I figured the white wire powered the car when I first saw it coming off the positive terminal on the starter solenoid, I just needed clarification on how. I suspect the actual gauge is my issue. I have 12V on the white wire at every point I can get to, including at the ammeter, but I get a no reading whatsoever at the negative terminal of the ammeter where the W/R wire attaches. I'll bypass the ammeter tomorrow and see if it solves my problem. I've got a few spare gauges laying around too, just in case of situations like this.

[Six_Shooter]

Many people replace the ammeter with a volt meter from a late 280Z. The most common way to bypass the ammeter when this is done is to attach those two wires together. When I did mine, I used a screw and nut, and then taped up the connection. It wasn't my preferred way to make the connection, but it has worked for 5 years this way.

[240z8]

What a coincidence, I'm staring at a ~76/77 280z volt meter right now comparing it to the 240z's gauge. Time for a little research. I'm fixing this Z with plans to drive it for a while and sell it, so I might as well make sure everything works right. I need the money for my 302 project. We bought a 92 YJ Wrangler with a Chevy 4.3 V6 and a Muncie SM465 that's nearly perfect minus none of the gauges working right; I figure if it irks me this much, it's going to be worse for someone that buys it and has to deal with the mess that I knew how to fix but didn't haha. Wiring is love/hate relationship for me, but it's worth it in the end.

[NewZed]

A "short" will create smoke and sparks and heat and drain the battery.  A break in the circuit will cause nothing.  

 

Don't forget that electricity has to get back to where it came from to make things happen.  The ground circuit is just as important as the supply circuit.  

 

I don't know the early Z's well, but most cars use relays to supply power to the various sub-harnesses.  Find the various relays and make sure they're working correctly.  Some relays ground through the case, so need to be mounted to work right.

 

atlanticz has a nice wiring diagram.  You'll need a computer, or a good eye on a phone.  http://www.atlanticz.ca/zclub/techtips/wiringdiagrams/72_240z_wiring.pdf

[240z8]

I swapped in another ammeter yesterday and it fixed my problem! Now it's time to research the fuel pump circuit.