RebekahsZ Posted July 21, 2012 Share Posted July 21, 2012 I was running down the road Thursday night and my dash lights looked dim (well, dimmer than usual), so I played with the rheostat under the dash. The dash lights then went completely out (the rheostat has been kind of sketchy for years). Later same night, somebody told me that my running lights were out, and dang it all, they were right. Brake lights work, emergency flashers work. Checked all circuit breakers with ohm meter and volt meter, all good. I went to the local z-graveyard and got another rheostat and replaced it. Still no dash lights or running lights. Did my drag racing with only the shift light for help, but did pretty well. Anybody know what the problem is (I already know I'm stupid, so please don't remind me)? Is there some commonality between the running lights and the rheostat? I don't know how to check the old or new rheostat properly. I do have a multimeter, just don't always know how to use it. Have wiring diagrams, but I missed out on that gene. Help? I got other parts of the car I want to work on!! and this stands in the way. Quote Link to comment Share on other sites More sharing options...
bjhines Posted July 21, 2012 Share Posted July 21, 2012 (edited) combi switch. I would say it is simple, but it can be a lot of other things. I think it is unlikely to be a problem with the dash lighting or dimmer. You might have one of the corner marker lights grounding to the body. I have had 2 240Zs with corner marker lights causing shorts. Edited July 21, 2012 by bjhines Quote Link to comment Share on other sites More sharing options...
dexter72 Posted July 21, 2012 Share Posted July 21, 2012 Are your fuses good and did you check them, No mention of that. Did you check the Headlight switch?. Quote Link to comment Share on other sites More sharing options...
Miles Posted July 21, 2012 Share Posted July 21, 2012 Usual suspect: headlight switch. Check out the headlight switch with a volt meter. In the past I have found broken/corroded contacts in the headlight switch to be the problem. Download one of the many pdf/JPG electrical schematics available here and highlight the dash and running light circuits. Then test the headlight switch at the appropriate contact points. If you have an extra working headlight switch just swap it with the old one. I keep a set set of TS/headlight switches around for quick trouble shooting and repalcement. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 21, 2012 Author Share Posted July 21, 2012 Wow fellas - thanks for all the help. Circuit breakers = fuses, sorry for the goofed terminology. I've been searching the internet and the forum..seems like the wire to start tracing is the green wire with the white stripe. I found the green wire coming from the headlight switch loose (pushed out of the connector) at the big white connector. Got all excited. Corrected that but (damn) it didn't fix the problem. The green and white wire has voltage when the switch is in the off position, but has no volts in the on position. Seems backwards - what do you think...?? Working on getting another headlight switch. I hate just swapping parts, but alas that is my sorry as_ way of doing things. More advice based on above? Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 21, 2012 Author Share Posted July 21, 2012 bjhines, by combi switch, you mean headlight switch, right? Quote Link to comment Share on other sites More sharing options...
Miles Posted July 22, 2012 Share Posted July 22, 2012 Wow fellas - thanks for all the help. Circuit breakers = fuses, sorry for the goofed terminology. I've been searching the internet and the forum..seems like the wire to start tracing is the green wire with the white stripe. I found the green wire coming from the headlight switch loose (pushed out of the connector) at the big white connector. Got all excited. Corrected that but (damn) it didn't fix the problem. The green and white wire has voltage when the switch is in the off position, but has no volts in the on position. Seems backwards - what do you think...?? Working on getting another headlight switch. I hate just swapping parts, but alas that is my sorry as_ way of doing things. More advice based on above? Headlight switch: You have several options - Buy a used one and hope that it works. - Learn to repair the one you have. There are several "how to" threads here and at Classic Z Car that explain how to repair the TS/headlight switch. You might as well because the switch will need servicing as long as you own a 240Z. - Buy a spare and repair it and your original switch so you always have a spare. -There is a member here (Dave) who repairs the TS/headlight combi switch for a very reasonable price. Do a search. He also developed and sells the headlight relay harness. I may have a link to the switch repair that I can post here later. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 22, 2012 Author Share Posted July 22, 2012 I'll do some more searching. I need to figure out a plan to TEST the headlight switch that I have and the one that I get. I hate just swapping parts not knowing what is wrong. Kind of reminds me of my previous live with triple side draft carbs..... Quote Link to comment Share on other sites More sharing options...
Miles Posted July 22, 2012 Share Posted July 22, 2012 (edited) Here is a headlight switch repair pdf you can download: http://www.kamikazer...ombo_switch.pdf Repairing the TS/headlight switch is easy. You'll need some small srew drivers, needle nose pliers, soldering iron, sand paper/nail files etc. Mostly it is cleaning carbon/oxidation off of the copper contacts and a little tweaking of the copper rockers and contacts. Edited July 22, 2012 by Miles Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted July 22, 2012 Share Posted July 22, 2012 Was a stereo recently installed? Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 22, 2012 Author Share Posted July 22, 2012 No, I was just minding my own business running down the road, till I tried to adjust the instrument rheostat. Then I almost got rear-ended by a couple of 8-second Mustangs on the return track when I stopped to move a big rock that stood between my oilpan and victory. That's when I figured out I had no tail lights. Heading out to junkyard after lunch for a (couple) of headlight and turnsignal switches. Same crappy stereo for 10 years; it works fine but only gets one station because I haven't wired my stupid antenna (thankfully it is a pretty good oldies station-if you consider '70s and '80s "oldies". Been focused on going fast. This stupid distraction is really aggrevating. I was planning on re-doing my rear suspension this weekend. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 23, 2012 Author Share Posted July 23, 2012 Learned a lot this weekend, but problem persists. Rebuilt the headlight switch. Got new resistor - bot resistors check out with new multimeter, although the new one is smoother than the old one. Headlight switch has power when it is in the off position, no volts in ON position - must be a short. Gonna try to check each running light next, although I don't really know how.... Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 23, 2012 Author Share Posted July 23, 2012 BJHines-thanks for your advice. I have replaced and checked my rheostat: both the old one and the new one are good (the old one has some spots that don't work good, but all in all it was OK). I rebuilt the headlight switch per a thread I found: it was ok too. I guess the fact that my fingers were adjusting the rheostat when this all went down was just a distractor to take me down a lilly path to nowhere! Now, it is on to the rest of the circuit. You said you'd been thru this twice before. Any advice before I move thru the harness to the marker lights (it had just rained like a mother right before the lights went out). How were your side markers grounding to the body? I haven't disturbed them in years - it was 20 years ago that the car was last painted! I'm a real idiot on electrical stuff, so please use short words and be as specific as possible. With the headlight switch in the OFF position, the green and white wire has 12 volts. If I switch the switch to the Running Lights position or the Headlights position, the voltage on the green and white wire drops to zero...does that mean that there is a short or an open somewhere? Quote Link to comment Share on other sites More sharing options...
bjhines Posted July 24, 2012 Share Posted July 24, 2012 Your test is inconclusive. It could very well be a short though. The marker lights can short out as the rubbers age or the parts corrode. There is a thin insulator in there that is easily bridged by rust. The chrome housing becomes live and the screws holding it in place will ground it to the body clip nuts and then to the body. Some other areas than cause problems are hot spots at the fuse holders, and some of the harness splices can also corrode. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 24, 2012 Author Share Posted July 24, 2012 bjhines- Lets assume it is a side marker grounding out: What is the fastest/easiest way to identify the offending side marker (I worry that disassembling each of them, cleaning and reinstalling could be inconclusive too). If I disconnect each side marker one at a time with the swith on, should the lights turn on as soon as the offending light is disconnected? Quote Link to comment Share on other sites More sharing options...
afbrian13 Posted July 24, 2012 Share Posted July 24, 2012 Thats one thing you can do-pull the bulbs from the marker lights in case one of them burned out and internally shorted. Its funny your having this problem because I just fixed the same thing (couple days ago) All my gauges and marker lights went out, but I still had headlights. Turns out the green-white wire coming out of the top of my headlight switch popped off. soldered it back on - gtg. That one stupid wire runs to all the lights except headlights, and all the gauge lights. It was pulling 6.5 amps on my car. Pretty sure thats why it heated up and un-soldered itself.Its up there under the plastic housing around the steering column. I'm running a 78 combo switch on my 76 because years ago thats what I had when my 76 switch fell apart. I just used the old switch to make an "adapter harness" from the 78 switch to the 76 car wiring so I can easily swap it back, if I ever need to. For a suspected short that keeps blowing fuses find some places to "break" the system. Wherever there are plugs under the dash you can unplug it. If it still shorts out its closer to the switch, if it stops it is in the part you just isolated. You said it started when you adjusted the dimmer. Thats a rheostat that is on the ground side of ALL those lights. They are all grounded though it (in a manner of speaking) if it broke inside that could be your issue. Hope some of this helps and good luck. Quote Link to comment Share on other sites More sharing options...
Miles Posted July 24, 2012 Share Posted July 24, 2012 Thats one thing you can do-pull the bulbs from the marker lights in case one of them burned out and internally shorted. Its funny your having this problem because I just fixed the same thing (couple days ago) All my gauges and marker lights went out, but I still had headlights. Turns out the green-white wire coming out of the top of my headlight switch popped off. soldered it back on - gtg. That one stupid wire runs to all the lights except headlights, and all the gauge lights. It was pulling 6.5 amps on my car. Pretty sure thats why it heated up and un-soldered itself.Its up there under the plastic housing around the steering column. I'm running a 78 combo switch on my 76 because years ago thats what I had when my 76 switch fell apart. I just used the old switch to make an "adapter harness" from the 78 switch to the 76 car wiring so I can easily swap it back, if I ever need to. For a suspected short that keeps blowing fuses find some places to "break" the system. Wherever there are plugs under the dash you can unplug it. If it still shorts out its closer to the switch, if it stops it is in the part you just isolated. You said it started when you adjusted the dimmer. Thats a rheostat that is on the ground side of ALL those lights. They are all grounded though it (in a manner of speaking) if it broke inside that could be your issue. Hope some of this helps and good luck. I had the same problem with with the green/white wire connection. Re-soldered it. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted July 24, 2012 Author Share Posted July 24, 2012 (edited) Thanks everybody. Checked rheostat, checked switch, now I'm trying to go thu each light bulb now. Weird thing is that I'm not popping fuses... Question: If there is a short in the green/white wire in the section I am checking, that wire should have zero volts and continuity with ground, right? ..instead of 12V? Sorry, I made a C- in electrical engineering 30 years ago, I really struggle with the basics. Getting close to towing car to an electrical shop, but that would be so lame... Edited July 24, 2012 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
beermanpete Posted July 24, 2012 Share Posted July 24, 2012 Yes, a short will have continuity to ground. From your description it sounds like it could be a bad connection somewhere. You have voltage without a load (lights off) and when you turn on the lights the voltage falls due to the load. This seems to suggest a high resistance (bad connection) upstream. Check the fuses, fuse connections, connectors, switches and so on. Probe the circuit along the path moving from the point you know has the voltage drop, moving toward the battery, until you find the point that still has 12 volts. The first component or connection past (on the load side) that point is the likely suspect. Quote Link to comment Share on other sites More sharing options...
Fuzzydicerule Posted July 24, 2012 Share Posted July 24, 2012 stupid question, did you check the bulbs for the taillights? Do your turn signals still work? or just the hazards? If not you might try replacing the hazard switch, i believe power for all the rear lights goes through that... Quote Link to comment Share on other sites More sharing options...
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