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Grounding issue? |
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amxgopack
AMC Apprentice Joined: Aug/15/2010 Location: Atlanta, GA Status: Offline Points: 56 |
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Posted: Jul/04/2018 at 3:57pm |
Help, I am not good at wiring pr electricity, but have an issue with my 1970 AMX. It just finished getting completely restored and a Painless wiring kit installed. It looks and sounds amazing. The problem I'm having is that while driving, the tech, voltmeter and fuel gauge go to zero occasionally. It may come back when I hit a bump, but not always. It is a problem because I think my alternator actually stops charging. My car has died while driving it before and it was due to a dead battery.
Any suggestions for things I should check first? Any obvious culprits? I took it to a shop before and they didnt see the issue. I want to drive and enjoy the car, but cant while I have this problem. Thanks for your help! Steve |
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amxgopack
AMC Apprentice Joined: Aug/15/2010 Location: Atlanta, GA Status: Offline Points: 56 |
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Bandana
AMC Nut Joined: Jul/26/2016 Location: NC Status: Offline Points: 473 |
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Can't help with the wiring but beautiful car! Is that the Commodore Blue?
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bigbad69
Supporter of TheAMCForum Joined: Jul/02/2007 Location: Ottawa, Ont. Status: Offline Points: 6609 |
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It sounds like you have multiple problems. If the alternator is not charging, that is a separate issue as it will not cause the symptoms you have described, other than a dead battery. Get yourself a DVM (digital voltmeter) - they're dirt cheap these days - and measure the battery voltage with the engine off. You should get 12.6V on a fully charged battery. Start the engine and rev it up a bit to make sure the alternator has started. Measure the battery voltage again. It should be up around 14V. If it is less, then you are under charging. It it is well beyond 14V then it is over charging. If the tach you have is the OEM model, then it is wired inline with the coil primary. If there is a bad connection, the engine will cut out when the tach stops taching. If you see the tach drop to zero and the engine continues to run, there is a problem with tach itself. The voltmeter and fuel gauge problems sound like loose connections to me. Hitting a bump shifts things around which can make or break the contact. It could also be a frayed wire which, when shifted to the right spot, contacts a part of the body and causes a short. That could be a possible cause of the dead battery if the charging system turns out to be good. Because it is an intermittent problem, it is harder to find. You will have to trace through the wiring for those instruments and verify all contacts are good and there are no shorts. Since you say you're not very good with wiring, I'm assuming someone installed the Painless kit for you. Maybe they should be the ones doing the grunt work since it wasn't done right in the first place.
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69 Javelin SST BBO 390 T10
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Online Points: 6755 |
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This could be the one issue as stated in the title of the post - Ground Issue.
The intermittent electrical faults of several instruments points to grounding. This could be the instrument cluster itself, engine to chassis or chassis to cluster. Try ground jumpers, wire engine to battery, engine to chassis and then chassis to instrument cluster. Since it starts and runs but the battery dies, it's likely engine to chassis but all should be checked. The problem with just checking with a meter is that at it's low voltage it may show fine but not when more amps are required. At high amperage when starting the poor ground can arc and the car will start but then at lower amperage draw the arc fails and so do the peripherals like instruments. Go over all the major grounding and then look for power supply issues. |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Doubtful it is one single issue if the alternator TRULY stops charging.......... the only ground is relies on is between the regulator and the alternator.
HOWEVER, you should check the GROUND STRAP from engine to cross member/chassis. Otherwise, most of the rest sounds like it is losing ground to the cluster now and then. Think of what these things have in common. The inside stuff really has almost nothing to do with charging, so a dead battery is one issue to check out, perhaps FIRST.
Like bigbad69 said, get a meter, Walmart for 20 bucks or less, and check the voltage at the battery with engine running a high idle. You are looking at about 13.8 (to 14.0) for a 1970 car (14.8 but the isolation diode will drop that .8 to 1.0 volts) If it's not doing at least the 13.8 you have a charging system issue PLUS the other stuff, which sounds like a ground at the dash cluster area. Keep in mind - what do those things have in common?? Do they all share the same ground? If you were losing power to the cabin, then the ignition switch would have nothing to send out to the ignition coil. (by the way, you don't have an ignition switch issue, do you?) Anyway, check the charging system and get that fixed and move from there, IMO. |
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amxgopack
AMC Apprentice Joined: Aug/15/2010 Location: Atlanta, GA Status: Offline Points: 56 |
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Thank you for all of the responses. It gives me a few things to try out before I take it to another shop. Yes it is Commodore Blue. Good eye.
I can't take it back to the shop because the shop is in Michigan, and I'm in Georgia. I sent it back once, and it spent another year up there. Considering it has been in the shop for nearly a decade getting restored, I don't think I have it in me to send it back for another extended stay. Thanks again all. Once I figure out the issue I'll post what I've found. |
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bigbad69
Supporter of TheAMCForum Joined: Jul/02/2007 Location: Ottawa, Ont. Status: Offline Points: 6609 |
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69 Javelin SST BBO 390 T10
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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True - but I was asking sort of to get someone to think it through, sort of like my old professors would do, or a boss I had at Compressor Controls, where we'd argue like lawyers, taking sides we didn't necessarily agree with, to force the other person to support their contentions.
You did exactly that - you knew the fuel gauge is grounded back there and only POWER goes to and through the gauge, and it's grounded at the tank. So, if it happens to the fuel gauge at the same time, it can't be ground, it must be SUPPLY side, or the (+) side of things. And that takes me to where I was starting - the power into the cabin, or at least the fuse panel area or the ignition switch (and I have had these EXACT same symptoms in my little Eagle years ago -exactly this - the switch supplied IGNITION but not power to the accessories - gauges, etc.). Depending on what keeps going - well, the ENGINE keeps running - ok, so it can't be the main power to the fuse panel as the ignition is sourced from that, too. Could it be at the ignition switch - where it keeps ignition feed but loses "accessory" feed (gauges, radio, blower, etc. all go through the ignition switch) Anyway, bigbad69 - thanks for supporting what I was attempting to do - get people to figure it out logically instead of throwing things at the wall and see what sticks. Ask "what do these things have in common". For the alternator or charging system, nothing. For the rest - you proved it's not a ground issue if it happens to the FUEL gauge, too.
But then we do need to consider that the cluster regulator requires a ground........ but if ungrounded the fuel gauge should peg as the regulator won't regulate (others please refer to TSM where is says regulator ground REQUiRED or you can FRY the gauges, bigbad69 already knows how that all works) So if the cluster regulator loses ground, it stops regulating and the gauges climb, not drop. Another piece of the puzzle indicating likely feed issue. LOGIC is your best friend in auto electric, tossing stuff at the wall to see what sticks is a way to spend many days, many dollars and still not get there. |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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Too bad you aren't closer, but then I have another SX4 to finish up wiring with a new engine bay harness and to complete repairs on the cabin wiring that some fool trashed years ago.......
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