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starts and dies

Sluggo

Sluggo

Active Member
Ok, so I have the mustang mostly back together and wanted to start and run it to test the vacuum motors for the ac and it won't stay running. It gets 12 volts from the starter relay to the coil and runs from that but once the relay de- energizes there is only 2 volts on the coil wire and it dies.

Sent from my HTC Inspire 4G using Tapatalk 2
 
"1497" said:
Too much resistance in the pink wire?
Click to expand...

I've found that the firewall plug for the coil/oil/water temp sometimes has high resistance across the junction and many 69/70 gauge (coil etc.) extensions are bad. Try tugging hard on the wires away from the molded plug. If that doesn't work, replace the gauge harness.
 
I ran a new wire from the connector to the coil using the connector I removed from the old alternator harness. The other wires are unused since I'm running oil and water temp gauges. I'll check it from the ignition to the connector next. I may just wire in a ballast resistor and be done with it. If that don't work ill put the Msd dizzy in it and get a 6al box.

Sent from my HTC Inspire 4G using Tapatalk 2
 
Looking at it here a few minutes ago, I'm only getting 2 volts at the harness side of the connector and it's quite warm to the touch. I need to resolve this whether I wire a ballast resistor around it or not.
 
"Sluggo" said:
Looking at it here a few minutes ago, I'm only getting 2 volts at the harness side of the connector and it's quite warm to the touch. I need to resolve this whether I wire a ballast resistor around it or not.
Click to expand...

That's seriously low. If you remove the connector to the coil leaving no way for current to flow, do you still get 2V or a full 12V when the ignition is turned to RUN? I've rarely seen bad resistor wires, but somewhere there is something adding resistance to the circuit. Have you looked at the ignition switch connector?
 
"Midlife" said:
That's seriously low. If you remove the connector to the coil leaving no way for current to flow, do you still get 2V or a full 12V when the ignition is turned to RUN? I've rarely seen bad resistor wires, but somewhere there is something adding resistance to the circuit. Have you looked at the ignition switch connector?
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I'm getting 2 volts with the pigtail from the connector to the coil completely removed from the car.

You have to consider all the other things I've done as well. I'm double checking the wiring to the alternator and regulator. I did have the lower dash loose and laying down on the right to get the evaporator in and out. The ignition connector looks ok visually but have not run any checks on it. Resistance wire is free and not pinched anywhere.
 
There's something very wrong here. With no current draw, you should get a full 12V at the end of the resistance wire.

Is this a 70 or a 69? Have you checked for a possible short up in the steering column (if a 70)?

You should have sent the harness to me like you originally intended to...
 
Check the grounds. Engine, battery and body to engine. If the system is not complete it may be pulling a ground through a light or rheostat.
 
"67 evil eleanor" said:
Check the grounds. Engine, battery and body to engine. If the system is not complete it may be pulling a ground through a light or rheostat.
Click to expand...

I drilled a 5/16 hole in the apron, put a 5/16x18 bolt through it from the outside gound the paint off the inside, put a washer and nut on the inside and tightened the hell out of it. I then ran separate grounds from the lug to the battery, lug to block, lug to headlight relays, etc. pretty confident in the ground system. I'll have time to look at it tonight. (I hope)
 
"Sluggo" said:
It would not matter if the cluster is not in place would it?
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Tach dash? If the tach is not connected or bypassed, there is no way for the current to flow to the coil. If you have a standard dash, the resistor wire goes straight from the ignition to the firewall plug. The ignition switch wire (green/red) also goes through the firewall to the voltage regulator (green/red wire)...aha! That might be your problem, senior!!!

You installed a one-wire alternator, yes? I'll bet it isn't hooked up correctly and is pulling voltage down at the ignition switch.
 
Just for giggles, why don't you run a jumper from the (-) side of the battery to the engine block and see if that helps. Booster cables will do and it will take only seconds to hook up. I'd also suggest using star washers between all ground terminals and the chassis. I'd check it also after plugging up the gauges, especially if there's a amp gauge in the cluster. They normally have a shunt to read off of and if it's not hooked up then that can explain the low voltage.
 
"67 evil eleanor" said:
Just for giggles, why don't you run a jumper from the (-) side of the battery to the engine block and see if that helps. Booster cables will do and it will take only seconds to hook up. I'd also suggest using star washers between all ground terminals and the chassis. I'd check it also after plugging up the gauges, especially if there's a amp gauge in the cluster. They normally have a shunt to read off of and if it's not hooked up then that can explain the low voltage.
Click to expand...

Naw...these amp gauges are really mini-voltmeters. They measure the difference in voltage between two points along the main power line going to the ignition switch with one point at the alternator to battery splice. When the amp gauge blows (and they do often enough!), everything works just fine.
 
:sm_NTA

except I originally thought the title of this post was referring to my sex life.
 
Figured it out.

As you recall, I replaced the solenoid with a relay that has two 87 outputs. I checked resistance on the pink wire and had 1.6 ohms from the green/red wire to the point where it splices to the pink wire. I checked the pink wire from the connector to the ignition switch and got 2.8. For shits and giggles I checked the pink wire from the connector to ground and got 3.6. :wtf

I've looked at this wiring diagram enough to draw it from memory and there's no way in hell there should be any path to ground with the circuit isolated. I pulled the starter relay and the path to ground went away. With the relay out I reconnected the coil wire and applied power to the 87 pole that goes to the stater and it started and ran like it should. I unpinned the other 87 wire that feeds 12v to the coil momentarily at startup, put the relay back in and it starts and runs fine.

So the relay is either bad on the second 87 or there is some sort of diode in it. The car starts by bumping the key without the momentary 12v boost so I'll just eliminate it from the circuit.
My first thought was that it would not be necessary but I chose to leave it in the circuit because it was there to start with. I now know better.

I have to work out a bug in my fan controller circuit and I not getting vacuum from the control panel to one of the vacuum motors. Those should be easy fixes.
 
speaking from experience, be sure & keep a couple extra relays in the car. for something that shouldn't go bad very often, it seems to happen a lot. I had a shit pot full of them in my 40 running door solenoids, fans, halogen brake lights, windows etc & always seemed to be replacing one.
 
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