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71 Mach Electrical problems.
#1
well I’ve got this old Mach running nicely, very cool, but some strange things are happening electrically.

The headlights and hazard lights work, but NOT the dash lights or turn signals. 
I thought the wiper motor was bad but when I ran a ground wire from the case to the firewall it works fine with the switch. The blower motor works, but not the radio. 
The ignition switch is new and the fuse box has all new fuses and I have 12V to all of the fuses.

I just bought the car and it has been sitting for a few years. Is there a common ground between these things? Or are all of these systems just broken? 
Running the ground strap and getting the wiper motor to work has me suspecting a common ground problem? 

Thanks again for the help.
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#2
What is your battery ground connected to? The correct way is to run from the negative battery terminal to the bottom screw on the voltage regulator and then to a bolt on the engine block. Most everything gets its ground from connecting to the body or dash. There are common ground wires under the dash that provide grounds to more than one component.

You can download a wiring diagram for your car in the Mustang Data tab at the upper right corner of this page.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
It has 1 large ground cable from the battery to a bolt right behind the alternator and that’s all. I also can’t see any ground strap going from the firewall to the engine. I would have thought if it were there I would be able to see it from up top. Any chance Ford would have put it down under the car? Sounds like I better put a couple more ground straps on?
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#4
(09-26-2019, 06:52 AM)Fordboy71 Wrote: It has 1 large ground cable from the battery to a bolt right behind the alternator and that’s all. I also can’t see any ground strap going from the firewall to the engine. I would have thought if it were there I would be able to see it from up top. Any chance Ford would have put it down under the car? Sounds like I better put a couple more ground straps on?
The diagrams leave a little to be desired in that they just show the battery going to ground. Some of the diagrams are labeled “14301 Assy” others just read “engine ground” 
I think I’ll add the wire to the VR mount and 1 from firewall to the back of the engine and see if anything changes. Thanks.
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#5
There was never a ground strap from the firewall to the block from the factory. I added one there and I also ran a 14 gauge wire from the front passenger side of the block to the frame.

run_horse Run Horse Run!
John 72 Q Code
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#6
The way that Ford did the battery ground was as I described above, battery to VR (on the fender apron) to the block. You can get a repop ground cable from Mustang vendors that has a tab that connects to the VR.

I agree with adding an additional ground from the firewall to the engine.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
  Reply
#7
(09-26-2019, 06:52 AM)Fordboy71 Wrote: It has 1 large ground cable from the battery to a bolt right behind the alternator and that’s all. I also can’t see any ground strap going from the firewall to the engine. I would have thought if it were there I would be able to see it from up top. Any chance Ford would have put it down under the car? Sounds like I better put a couple more ground straps on?


As others have said, add one from the battery to the fender apron, or engine block to apron. If that ground connection is missing, it can cause all sorts of electrical gremlins. 

The Ford method was kind of half-assed as the VR screws are very easy to strip out. I welded a bolt into the apron on my '71 to serve as a permanent ground location.


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#8
Could be a common ground issue - Midlife would be able to tell for sure.

I would also check your fuses, as well as the fuse block itself.  I was getting mine inspected a few years back and the horn wasn't working... worked fine the day before, though.  I wound up having to abandon the inspection and go home to troubleshoot.  I tested the fuse (both sides) and it had power, but the 'horn' side of the fuse socket had just enough carbon build up that it prevented the circuit to complete.  Once I cleaned it all up and went back for re-inspection, it was all good.

Eric

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#9
You guys are awesome! I added a cable from batt — to the VR mounting screw and instantly the turn signals and gauge lights worked. I added a strap from the firewall to the engine block and the gauges started working, Plus the gauge lights got brighter.
....and to think my wife said you guys would be a bad influence on me..... don’t tell her I was here...
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#10
(09-27-2019, 07:06 AM)Fordboy71 Wrote: You guys are awesome! I added a cable from batt — to the VR mounting screw and instantly the turn signals and gauge lights worked. I added a strap from the firewall to the  engine block and the gauges started working, Plus the gauge lights got brighter.
....and to think my wife said you guys would be a bad influence on me..... don’t tell her I was here...
Yay! 
If you want, you can tell her that we are only a pack of Internet Ax Murderers.  That's what my wife warned me about when I began using the Internet...

Let me check your shorts!
http://midlifeharness.com

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