bjhines Posted March 4, 2008 Share Posted March 4, 2008 I kid you not!!!! The power to run your coil+ has to travel 44'(thats fourty-four feet) down 18 gauge wires with no fewer than 9 connections and 2 splices. AND THIS IS JUST FROM THE IGNITION SWITCH!!! That does not include the numerous splices and connections from the alternator to feed the ignition switch in the first place. Holy crap!!!! 44 feet!!!! through 18 gauge wire!!!! No wonder the ignitions suck on these cars. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted March 4, 2008 Administrators Share Posted March 4, 2008 Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted March 4, 2008 Share Posted March 4, 2008 LOL, bored? Quote Link to comment Share on other sites More sharing options...
bjhines Posted March 4, 2008 Author Share Posted March 4, 2008 I have wire hell in my garage right now. The culled pile is getting as big as the keep-pile. This is not my first rodeo. I was just surprised at the layout of the ballast resistor and coil arrangement. The tach needs the coil+ run through it's sensing loop. The start key bypasses the ballast resistor. These are the only reasons I can see for this extremely long rat-maze. I have always used this arrangement in my 240Zs just bypassing the resistor and connecting the green-white and black-white that span the resistor. My l24 powered 240Z just has the bypassed ballast with a higher impeadance coil. I will have to see about shortening this up with a splice under the right corner of the dash. I can effectively shorten the run to ~22' in an easy to reach location. I could shorten it to ~14' with an slight unwrap of the harness near the tachometer. That would require pulling the dash. I don't think I could work through the tach-hole or from underneath. Quote Link to comment Share on other sites More sharing options...
bjhines Posted March 4, 2008 Author Share Posted March 4, 2008 Something else comes to mind. correct me if I am wrong... The IGN black-white goes dead when the key is in the start position. The IGN black-white also runs the gauges and accessories. It looks like they are supposed to shut off when the start key is engaged. The coil gets power via. the green-white wire in the start position so the ignition works. Everything else shuts down(except the lighting circuits and the cigarette lighter). The thing is, My car's gauges work when the key is in the start position. The lack of a ballast resistor means that they back feed from the bypassed ballast-resistor back into the IGN circuits. This backfeeding is probably not good. That long 18g wire run is not sufficient to handle the loads that might be placed on the IGN circuits. There is potential for a fire hazard if the starter is engaged for longer than normal periods of time with all the IGN related loads ON. I have an idea to solve the problem. I use a 5 amp Diode in place of the ballast resistor. Cathode on the Green-white. I have a box of metal body diodes somewhere. I need to start referencing some numbers. Quote Link to comment Share on other sites More sharing options...
bjhines Posted March 4, 2008 Author Share Posted March 4, 2008 There is no fuse on the IGN coil circuit!!! NO wonder I have seen them with melted wires so often. Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted March 4, 2008 Share Posted March 4, 2008 There is no fuse on the IGN coil circuit!!! NO wonder I have seen them with melted wires so often. Other than new cars (less than 10 years old) I haven't see an actual fuse on the ignition signal. Before that there were fusable links most commonly, and these were always pre-ignition switch. Newer cars yet are even worse with relay or solid state driven coil positive circuits. Take a look at some ignition schematics for newer GMs (2006ish+) there's no start wire. Chrysler has tried something similar, but has a "second starter wire", that is resistance based to ground, whihc also carries other switch information also based on resistance information to ground. The "backfeeding" that you see, may not be "backfeeding", or at least not un-intentional. I have seen on some older vehicles that use balast, and some that don't have balast resistors, and use a start bypass circuit will actually power other devices, like guages, and such while cranking. This has been completly intentional in these cars. Quote Link to comment Share on other sites More sharing options...
bjhines Posted March 4, 2008 Author Share Posted March 4, 2008 I have really studied the wiring on this 1973 240Z. Mine is a 1973 June build month. It really has a lot more wiring than either of my 1972 models. I have also unwrapped a 1972 harness. The wiring is the same but simpler mainly due to the lack of EGR relays and sensors. The washer/autowipe also adds a great deal of complexity. Unless I am completely missing something, On a stock 240Z... When starting the car, The only voltage that goes to any of the guages and related IGN circuit devices is forced to back-feed through the ballast resistor. This may allow partial-voltage operation of these devices. I dunno... The resistor ensures that any power backfeeding is greatly reduced and incapable of heating the wires. There is NO FUSE on this circuit(only a ballast resistor). These are small 18g wires. These wires are the longest runs in the vehicle. They are capable of ruining the ENTIRE HARNESS if they do melt. The problem I forsee comes from the fact that bypassing the ballast-resistor removes the current limiting imposed on the stock configuration. Bypassing the resistor could lead to burned wires if IGN circuit devices have been added... and are all ON while starting the car. This is a good example of why you should always use relays to power new components you add to your stock electrical system. The potential for fire or harness damage is greatly increased with seemingly small modifications to your electrical system. In this case, the ballast resistor ALSO serves to LIMIT CURRENT in the coil+/TACH/IGN circuit when starting the car. Quote Link to comment Share on other sites More sharing options...
bjhines Posted March 5, 2008 Author Share Posted March 5, 2008 Here is a diagram of the stock Ignition circuit ... Quote Link to comment Share on other sites More sharing options...
DCZ Posted June 14, 2010 Share Posted June 14, 2010 Here is a diagram of the stock Ignition circuit ... Hey John, This post came up in my search so you might have some insight. The other night, while I was driving my 73/turbo the tach needle started bouncing wildly then died to zero. At the same time my temp, oil and fuel gauges (all stock) went dead. Ammeter still works. Everything else appears to work fine and the car runs so I know the current loop in the tach is still connected since that is how the coil gets it's signal. Where do you think the problem is? I'm guessing a common ground or power wire. I've been poring over the schematics and the gauges appear to have a common ground but I don't know where physically that wire is. They may also have a common power but I'm not sure exactly where that is either. Any ideas on where to look first, Oh Shredder of Wiring Harnesses? Thanks! Quote Link to comment Share on other sites More sharing options...
ktm Posted June 16, 2010 Share Posted June 16, 2010 The 240z gauges do not share a common ground.....well, I guess they do in a sense. The gauges ground themselves on the gauge housings. Quote Link to comment Share on other sites More sharing options...
DCZ Posted June 16, 2010 Share Posted June 16, 2010 The 240z gauges do not share a common ground.....well, I guess they do in a sense. The gauges ground themselves on the gauge housings. Are you sure about that? The FSM diagram shows a Black wire going to the clock, fuel/oil, water temp, and tach. That wire is shown to go to ground as well. I'm hoping someone may have had the same symptoms and could point me to a specific place in the harness to look into before I tear the whole dash apart . . . Quote Link to comment Share on other sites More sharing options...
ktm Posted June 16, 2010 Share Posted June 16, 2010 (edited) Edit: Wait, I am confusing the gauge lights ground. They ground on the housing. Review the wiring diagram again and you'll see that the water temp, fuel/oil and tach are all on the same fused circuit. Follow the YR lines on the water temp and fuel/oil gauges and the positive terminal on the tach. Check the fuse as well. Edited June 16, 2010 by ktm Quote Link to comment Share on other sites More sharing options...
sicj Posted June 17, 2010 Share Posted June 17, 2010 I have a problem with the black/white wire running from the IGN switch to the coil... The car has a 280zx elec. distributor in in when I bought it. Started cutting out randomly. Finally would never restart. -I get 12v+ without the distributor hooked up @ the blk/wht wire by the coil. -Hook the dist. to the coil no more 12v. Car won't start. found the blk/wht wire under the colum was rubbing on the underside of the steering colum. Looked like it was grounding out causing a short. fixed that, still no start. -Ran 12v+ to the coil straight from the batt. to the coil, car starts. -Add a switch and a relay to control the coil/ign F trying to find another short through 44' of wire. I now have excellent 12v+ with better cranking and killswitch Quote Link to comment Share on other sites More sharing options...
AkumaNoZeta Posted June 17, 2010 Share Posted June 17, 2010 What about installing a 280ZX distributor and run a relay for the coil (since you don't need a resistor with the newer part) so you can use direct battery voltage with bigger wire to it? Quote Link to comment Share on other sites More sharing options...
DCZ Posted June 17, 2010 Share Posted June 17, 2010 Problem solved! I started with the basics: Cleaned grounds at the battery, starter, fender well -- no change. Then I checked all the fuses with an ohm meter, cleaning as I went -- no change. Then I checked all the electrical connectors I could reach under the dash, wiggling and snugging each one -- no change. Then I pulled the cover from beneath the steering column and checked/wiggled all the connectors for the ignition, combo and turn signal switch -- BINGO! So I'm still not sure of the exact cause but it probably had to do with the turn signal switch, since I noticed that the turn signals were not working when the gauges were out. Quote Link to comment Share on other sites More sharing options...
DCZ Posted June 17, 2010 Share Posted June 17, 2010 Edit: Wait, I am confusing the gauge lights ground. They ground on the housing. Review the wiring diagram again and you'll see that the water temp, fuel/oil and tach are all on the same fused circuit. Follow the YR lines on the water temp and fuel/oil gauges and the positive terminal on the tach. Check the fuse as well. You're right about the gauge lights. I have a loose one in my speedometer and it's driving me crazy. Wiggle, wiggle - ON, wiggle, wiggle - OFF! Quote Link to comment Share on other sites More sharing options...
bjhines Posted July 13, 2010 Author Share Posted July 13, 2010 Ooops.. I totally missed this one. I'm glad you found the problem. I eliminated all of the stock dash/guage/tach wiring on my new project. Quote Link to comment Share on other sites More sharing options...
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