matt_w Posted June 3, 2011 Share Posted June 3, 2011 (edited) I pulled my dash to install new gauges, and I happened to notice that a large majority of the ground leads (to the gauges, a few switches, etc) are melted. The wire is still there, but all the insulator is melted. One of the big connectors on the side got melted because a ground wire running through it got so hot. How did this happen? I wonder this as I go through and repair all the damage. Did someone connect the battery backwards or something? One incident happened awhile ago where the battery slid on the tray while it was being driven and the positive lead arced out on the frame and the entire battery caught fire. I don't think that would have done this, but maybe it did? 1973 240z Edited June 3, 2011 by matt_w Quote Link to comment Share on other sites More sharing options...
dexter72 Posted June 3, 2011 Share Posted June 3, 2011 (edited) You answered your own question in your post, Now its time to fix those ground wires. A battery hold-down is your cars friend. Edited June 3, 2011 by dexter72 Quote Link to comment Share on other sites More sharing options...
matt_w Posted June 3, 2011 Author Share Posted June 3, 2011 How would that cause it though? Wouldn't all the current go directly from the battery to the frame at the point of contact? Quote Link to comment Share on other sites More sharing options...
rsicard Posted June 3, 2011 Share Posted June 3, 2011 How would that cause it though? Wouldn't all the current go directly from the battery to the frame at the point of contact? Poor grounds will become heater wires, like toaster elements, at their weakest points. When replacing them use the next gauge heavier wire and make them all come to a common point. Then use a heavy gauge wire from the common point back to the negative post of the battery. Then get a kit for the headlights which includes relays to take the heavy current off of the headlight switch on the column and transfer that heavy current load to the new relays in the kit. Then get the turn signal and headlight switches rebuilt. The same should be done for ALL the heavy current wires routed behind the dash. Also inspect the back side of the fuse panel for any poor connection and clean them up and resin core solder any poor connections there. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 3, 2011 Share Posted June 3, 2011 How would that cause it though? Wouldn't all the current go directly from the battery to the frame at the point of contact? And through all the wires connected to the chassis as grounds. Its a circuit. Quote Link to comment Share on other sites More sharing options...
matt_w Posted June 3, 2011 Author Share Posted June 3, 2011 Poor grounds will become heater wires, like toaster elements, at their weakest points. When replacing them use the next gauge heavier wire and make them all come to a common point. Then use a heavy gauge wire from the common point back to the negative post of the battery. Then get a kit for the headlights which includes relays to take the heavy current off of the headlight switch on the column and transfer that heavy current load to the new relays in the kit. Then get the turn signal and headlight switches rebuilt. The same should be done for ALL the heavy current wires routed behind the dash. Also inspect the back side of the fuse panel for any poor connection and clean them up and resin core solder any poor connections there. Fair enough. I've already swapped out most grounds (that are behind the dash) by using thick-gauge wire diretly to the steel frame of the dash, then I have a large wire (in addition to the stock wires) running from that to the frame. That should cover me right? Where is a good place to get a headlight relay kit? When you say rebuilt switches, are you just referring to taking them apart and cleaning up the contacts? Are you also recommending to replace heavy-current wires behind the dash or do you mean something else. Thanks for the advice, and a big middle finger to the guy who thought it would be a good idea to secure the battery down with a zip-tie Quote Link to comment Share on other sites More sharing options...
rsicard Posted June 3, 2011 Share Posted June 3, 2011 And through all the wires connected to the chassis as grounds. Its a circuit. I think what John is saying is the body and frame are the ground or return side of the circuits. The connections between the different electrical components and the body/frame are all dependent upon how good the electrical connection is back to the negative post of the battery. If there is a weak (connections) or inadequate gauge wire from the negative post of the battery to the body/frame, then ALL the electrical circuits that use the body/frame as the return path back to the negative post of the battery will be electrically WEAK. Using properly sized wire, per circuit current carrying requirements, will ensure there is GOOD electrical performance for those circuits. Good grounds/circuit returns are the other 1/2 of the circuit. A POOR return path make a POOR electrical circuit. Same is true for the positive side of the circuit. Not relying on the body/frame ensures a good circuit for the ground/return side. When gathering together grounds to a central point, the return path to the negative post of the battery needs to be even heavier gauge wire to carry ALL the current of all the circuits tied to it. Quote Link to comment Share on other sites More sharing options...
rsicard Posted June 3, 2011 Share Posted June 3, 2011 Fair enough. I've already swapped out most grounds (that are behind the dash) by using thick-gauge wire diretly to the steel frame of the dash, then I have a large wire (in addition to the stock wires) running from that to the frame. That should cover me right? Where is a good place to get a headlight relay kit? When you say rebuilt switches, are you just referring to taking them apart and cleaning up the contacts? Are you also recommending to replace heavy-current wires behind the dash or do you mean something else. Thanks for the advice, and a big middle finger to the guy who thought it would be a good idea to secure the battery down with a zip-tie When is come to rebuilt switches, you can do this yourself if you are CAREFUL. Mark the wires before disconnecting the stalk switches on the steering column such that there is no doubt when putting same back together. Then find a good workspace and CAREFULLY open one switch at a time and clean same. When cleaned smear silicon grease onto the switch portion and close back up. Do this to the other switches. The headlight relay kit is available from www.motorsportauto.com/products.html. May not need to replace heavy-current wires behind the dash so long as they are not damaged. Strong suggestion: Just inspect for a good ground/return electrical path back to the battery negative. Make certain there is a heavy-gauge wire between battery negative and the body/frame for a GOOD return path from all cabin circuits back to the battery negative. With all of this you should do just fine. If there are any further questions, don't hesitate to ask. Quote Link to comment Share on other sites More sharing options...
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