More Electrical/Idle Problems

[icejawa]

There ya go!  Somewhere between the plug from the harness and the coil, it is losing a lot of voltage.  Even repro harnesses may not be as good as you think.  You can measure the resistance between the coil lead and the male pin on the gauge feed plug to see if it anomalous (greater than ~ 1 ohm).

Any idea on where to get a good one? I'll check out the resistance but it looks like this may be the problem all along.

Don C's suggestion also sounds likely but I am unsure as to how to test for that

 

[Don C]

The best way to check just the switch (a little difficult) and rule out any other connectors or wires is to check the continuity between the solid yellow wire and the red/light green stripe wire at the ignition switch connector (under the dash on top of the steering column), with the ignition key in the run position.

 

[midlife]

There ya go!  Somewhere between the plug from the harness and the coil, it is losing a lot of voltage.  Even repro harnesses may not be as good as you think.  You can measure the resistance between the coil lead and the male pin on the gauge feed plug to see if it anomalous (greater than ~ 1 ohm).

Any idea on where to get a good one? I'll check out the resistance but it looks like this may be the problem all along.

Don C's suggestion also sounds likely but I am unsure as to how to test for that

I prefer National Parts Depot and Virginia Classic Mustang as national Mustang catalog stores.  Don at OMS will know what is best (most likely Alloy Metal Products).

An easier test is to measure voltage at the fuse box with key in RUN (don't do this if you run points, or if you do, disconnect the coil lead).  Check the 2nd down fuse on the right side (just above the smallest fuse), most interior clip.  This should provide the voltage coming out of the ignition switch for the run circuitry.  The fact that you saw 8.1V at the coil lead but 11.5 at the plug for the engine gauge feed harness says that the voltage drop is between these two points.  I always advise getting a new engine gauge feed harness if you have any doubts whatsoever.  Of the 3 dozen or so that have come in for checks, maybe 2 have passed.  These harnesses see all of the heat, stress, etc. of being in the engine compartment and folks just love to butcher them, and cover up the bad splicing practices with tape so you can't see that there was a splice.

 

[icejawa]

There ya go!  Somewhere between the plug from the harness and the coil, it is losing a lot of voltage.  Even repro harnesses may not be as good as you think.  You can measure the resistance between the coil lead and the male pin on the gauge feed plug to see if it anomalous (greater than ~ 1 ohm).

Any idea on where to get a good one? I'll check out the resistance but it looks like this may be the problem all along.

Don C's suggestion also sounds likely but I am unsure as to how to test for that

I prefer National Parts Depot and Virginia Classic Mustang as national Mustang catalog stores.  Don at OMS will know what is best (most likely Alloy Metal Products).

An easier test is to measure voltage at the fuse box with key in RUN (don't do this if you run points, or if you do, disconnect the coil lead).  Check the 2nd down fuse on the right side (just above the smallest fuse), most interior clip.  This should provide the voltage coming out of the ignition switch for the run circuitry.  The fact that you saw 8.1V at the coil lead but 11.5 at the plug for the engine gauge feed harness says that the voltage drop is between these two points.  I always advise getting a new engine gauge feed harness if you have any doubts whatsoever.  Of the 3 dozen or so that have come in for checks, maybe 2 have passed.  These harnesses see all of the heat, stress, etc. of being in the engine compartment and folks just love to butcher them, and cover up the bad splicing practices with tape so you can't see that there was a splice.

I'll be sure to test that tomorrow, my mach usually takes like 5 cranks to actually catch, then 1 more to fire up all the way. I was never sure if that was a dead give away to the problem being the ignition switch or the engine feed harness, since bypassing the harness with a wire from the battery to the coil would make it take only 1 crank to fire it up.

 

[icejawa]

I ordered a new ignition switch and the engine harness as well I hope those fix this problem, then I can move onto tidying up

I measured the voltage at every fuse and they all seem to be around 12V

So when I go to replace the ignition switch, how do I get to it? Is it located under the plastic cylinder cover on the steering column?

 

[Don C]

No, it's further down. About the only way to get to it is to lower the steering column. You don't have to disconnect the rag joint under the hood, just remove the plastic cover plate and bolts that hold it to the dash. You'll then be able to reach it. When you install the new one it has to be adjusted so it works properly. Leave the key turned off, I would even remove the key from the lock, you don't want the geared portion of the switch rod to pull out of the ignition lock, or you'll have to remove the lock so you can get the gear teeth meshed correctly.

Disconnect the battery cables before you start.

 

[icejawa]

No, it's further down. About the only way to get to it is to lower the steering column. You don't have to disconnect the rag joint under the hood, just remove the plastic cover plate and bolts that hold it to the dash. You'll then be able to reach it. When you install the new one it has to be adjusted so it works properly. Leave the key turned off, I would even remove the key from the lock, you don't want the geared portion of the switch rod to pull out of the ignition lock, or you'll have to remove the lock so you can get the gear teeth meshed correctly.

Disconnect the battery cables before you start.

I saw a thread on another mustang site claiming you could do it without lowering the column if you can fit down there. I'll try to lower the column but if I can't figure it out I will have to try something else since I'm small enough to fit in there with the door open,

 

[Don C]

Good luck, tight spaces and sharp metal edges. I know I can't do it without dropping the column. Just takes a couple of minutes to drop the column and not have to spend much longer than that trying to be a contortionist.

 

[icejawa]

Good luck, tight spaces and sharp metal edges. I know I can't do it without dropping the column. Just takes a couple of minutes to drop the column and not have to spend much longer than that trying to be a contortionist.

I got the new engine gauge feed harness in, no change. I took the ignition switch out so far, and it looks ghetto rigged, hopefully this new one fixes that problem.

Update: I got both the new engine harness and the new ignition switch in. The car still stalls when I turn the headlights on unless I have the pedal down a little. I tested the positive coil lead and it shows slowly but surely 12V on my voltmeter. I'm at a loss now lol but I'll check the grounds again

 

[Fabrice]

That's better than 8 volts!

Is the battery in good condition/fully charged? About the lights bulbs, what are they? H4's 40/45 amps or more?

 

[icejawa]

That's better than 8 volts!

Is the battery in good condition/fully charged? About the lights bulbs, what are they? H4's 40/45 amps or more?

Battery is new and charged, I just checked. The bulbs are reproductions I'm not sure of the amps, I will have to check. Right now I am checking the grounds and I can only seem to find the one from the negative battery post to the engine block. There is a fastener coming from the engine block bolt for the wire to the starter. In the picture I loosened the bolt and realized I should take a picture so thats why its loose. Shouldn't there be more grounds around town? I'm not sure of the locations exactly

 

[midlife]

There should be a ground from the back of the passenger side head to the firewall: it is a bare braided strap of wire, but it is very important. This is your chassis ground.

 

[icejawa]

There should be a ground from the back of the passenger side head to the firewall: it is a bare braided strap of wire, but it is very important.  This is your chassis ground.

You mean this bolt with nothing on it? !

 

[midlife]

Could be...I'm not as familiar with the 7123's by sight; I owned 65/66's.

 

[icejawa]

Could be...I'm not as familiar with the 7123's by sight; I owned 65/66's.

Ah ok. I got a ground wire there now anyways and I still get the same problems. When I jump the positive post to the positive ignition coil post the car runs fine. Could a bad ignition coil cause this?

 

[Don C]

Yes, a bad coil can breakdown internally when it gets warm

 

[midlife]

But wouldn't a bad coil also go bad running off of battery voltage instead of the coil wire?

Icejawa: are you running halogen headlights by any chance? Does the car run OK without the headlights on?

 

[icejawa]

But wouldn't a bad coil also go bad running off of battery voltage instead of the coil wire?  

Icejawa: are you running halogen headlights by any chance?  Does  the car run OK without the headlights on?

I have the halogen and the car runs ok without the headlights on. I ordered a new ignition coil just for the hell of it since this ones a 10 year old MSD coil with oil which wasn't mounted properly by the previous owner

When I turn the headlights on while I have the post jumped to the coil the engine will briefly drop but just lightly and quickly. Not enough to stall it out like it does without me jumping it

The car backfires like hell and takes like 7 cranks to finally fire up fully. When I did drive it the car would buck often and I thought I was just a crappy driver. The new wire harnesses and ignition switch clearly are helping volts pass easier though so its a step forwards.

 

[Fabrice]

Halogens.mmmm, thats why I asked about the lights bulbs.

And you have added relays or just replace the bulbs with these?

Few tests I'd do at this point. Engine off turn headlights on. Do they pop full capacity in the instant you put them on or is it more like a fade in and not really as bright as they should be? Replace the hallogens with basic H4 old fashion incandescent 40 amps bulbs.

The grounds, having at least 2 straps is good, 1 at block cyl 1 to and one rear engine to firewall. Having them with good bare metal to strap is better. The lights circuit as well. There are 2 wires near the headlights screwed on metal. Don't know the name, but they are flat, like a washer with a wire to it. Make sure these also have good contacts.

I don't think the coil replacement will fix. It will help giving better sparks and may be so mask the prob a bit.

Also, as its hard to fix electrical issues via text, keep in mind that even if some questions may sound silly or out of context, your answers to them help us get better idea of what is going on via elimination...

 

[icejawa]

Halogens.mmmm, thats why I asked about the lights bulbs.

And you have added relays or just replace the bulbs with these?

Few tests I'd do at this point. Engine off turn headlights on. Do they pop full capacity in the instant you put them on or is it more like a fade in and not really as bright as they should be? Replace the hallogens with basic H4 old fashion incandescent 40 amps bulbs.

The grounds, having at least 2 straps is good, 1 at block cyl 1 to and one  rear engine to firewall. Having them with good bare metal to strap is better. The lights circuit as well. There are 2 wires near the headlights screwed on metal. Don't know the name, but they are flat, like a washer with a wire to it. Make sure these also have good contacts.

I don't think the coil replacement will fix. It will help giving better sparks and may be so mask the prob a bit.

Also, as its hard to fix electrical issues via text, keep in mind that even if some questions may sound silly or out of context, your answers to them help us get better idea of what is going on via elimination...

The headlights fade on with the engine off. I don't think they guy before me put any relays in from what I can see. I also am not sure where to find the right bulbs, it seems all the online sites sell halogens. After work I will have to check those headlight circuit contacts.