Starting Issues

[Gage25]

hey guys, I have a 1971 bronco with a centech wiring harness. The other day I pulled the heater box to replace the heater core got everything back in and together and went to start my bronco and it cranks and starts for a second but dies as soon as I let off the key. If I hold the key in start and hold the gas pedal down it will rev up then keep cranking but die when I let off the key. I have replaced the starter solenoid and ballast resistor. traced the wires and can't find a break. Also recently put a new TBP ignition switch in.

 

[DirtDonk]

The new switch might be the culprit if you installed if before this issue cropped up.
But check your fuses first. I don't remember if the Centech panel has an ignition fuse or not, but it's worth a look.

No reason to replace the starter relay/solenoid. You could test the relay by disconnecting the "I" wire. I think it's a White, or one of the Blue wires? White I think.
If you disconnect it and still have the issue, it's NOT the starter relay.
Easy to check the ballast-resistor too, with a multi-meter. They certainly can fail, but rarely do, so not as likely the issue. But it would certainly give you the same symptoms if it had failed.
Just measure the voltage on the output side of the resistor.

What you're experiencing is no power to the ignition (coil or module) when the key is in the ON position. That's either the switch, or the wiring to the coil and/or ignition module if you're running one. Basically it shows your starter relay is working as expected, as it is providing power through the I terminal to the ignition components during START.
What type of ignition are you running?

Paul

 

[Gage25]

it does have an ignition fuse I will change that out tomorrow. its and electronic ignition system Im just not sure what kind. I believe the distributor is mallory if Im remembering correctly. Is the S post on the solenoid supposed to be hot while ignition is the on position? I tested it with a test light and mine is not. What wire is supposed to feed power from the ignition switch while in the on position? sorry if I'm not making sense this is all pretty new to me.

Thanks Paul

 

[gr8scott]

Is the S post on the solenoid supposed to be hot while ignition is the on position? I tested it with a test light and mine is not.

The S post is only hot when the ignition is in the start position. If it were hot in the on position, the starter would spin continuously.

 

[Gage25]

thank you!

 

[gr8scott]

Hey Gage25, as Paul asked, What type of ignition are you running? You should become a member and post up a bunch of pictures. It's
a steal at only $12/year. I also run a Centech harness. The blue IGN wire and the white wire from the I post of the starter relay/solenoid
should be connected to the same end of the ballast resistor. The wire on the opposite end of the resistor connects to coil positive.
Got a multimeter? If so, with the key on, measure voltage at coil positive. Should be ~6-8 volts.

 

[DirtDonk]

its and electronic ignition system Im just not sure what kind. I believe the distributor is mallory if Im remembering correctly.

Maybe even pop the cap off of the distributor to take a peek inside. Even Mallory has had different trigger mechanisms available at the same time over the years.
Or maybe we can tell just by the connector. If it's got Orange and Purple wires (I think those are the common colors?) then maybe we can go from there.
But as said, pics help a lot!

We need to find out if it's a self-contained electronic ignition, inside the distributor, or if it feeds an ICM (ignition control module, or just "box") mounted externally.
This would add another possible connection that might have failed while other work was being done.

Since you were under the dash working on the heater box, you might take a peek underneath (if you can twist your head and neck around like that!) to hunt for any hanging wires or kinked splices.

What wire is supposed to feed power from the ignition switch while in the on position?

From the factory these wires come through the firewall behind the engine, but with Centech they come from over on the passenger side fender area (unless changed and re-routed by the installer) and are as Scott described. There are two different Blue ones and a White one from the starter relay. Find the connector with at least two of those and make sure it's still in good shape and that the wires are as Scott described at the ballast resistor.
I forget what is written on the White one, but the Blue ones should say something like "IGN + Power" or similar.

Probably something simple.
Which is why the multi-meter is such a handy tool. Even if you don't do all the work yourself, you can still do the initial testing and find out if power is getting to the coil AND/OR ignition control module when the key is ON.

Remember you changed the ignition switch before this started too, correct? Was it at the same time you did the heater work? Maybe a quick check at the ignition switch connector (Centech version about 6" away from the switch) to be sure that power is being delivered with the key ON.

Good luck!

Paul

 

[Gage25]

Okay the blue wire that is alone on the ballast resistor is ign power white and purple wire on the other side is start and I term. The purple start wire runs from the resistor straight to the negative side of the coil and is ran on it’s own it doesn’t go through the plug in the harness. The purple start wire that is part of the plug has been rolled up and taped for some reason. The ignition is a Mallory e- spark. And there is a green red and brown wire coming out of it the green wire is hooked to the positive side of the coil and red wire is connected to the negative side of the coil along with the purple start wire. Brown wire is attached to the block with negative terminal coming off battery. Why would there be a separate purple wire that is ran straight from the resistor to the coil? Looks like I’ve got a mess here but it ran like this for the past year and a half I’ve had it and haven’t touched or switched any of the wires

 

[Gage25]

I changed the ignition switch a few weeks ago it has ran fine until I pulled the heater box that’s when it started.

 

[Gage25]

I have no power to the positive side of the coil when in the on position only while in the start position. While the key is on the red wire and whit wire at the back of the switch has 12 v but the purple wire has zero.

 

[gr8scott]

I guess i mis-spoke in my previous post. The way your ballast is wired is correct.

 

[Gage25]

Well, it was a fuse.. I had checked the ignition fuse but the alt/emm fuse was bad.. I’ve been at this for days chasing wires and it was a fuse!! Thanks for your guys help now onto the next, aligning my doors...

 

[gr8scott]

And I was just about to ask you if you had 12 volts to the blue IGN wire at the ballast resistor. Glad you figured it out.

 

[DirtDonk]

And FYI the Purple wire in these and all GM-based wiring color schemes is for the START position. It's the other end of the "S" wire (for "start" or "switch"?) that you see down on the starter relay.
So it not having voltage in ON is proper and correct.

Paul

 

[DirtDonk]

Okay the blue wire that is alone on the ballast resistor is ign power white and purple wire on the other side is start and I term.

You don't need both. The White is the one that should be on the coil side of the resistor, but if the Purple is the only other one, then the installer re-purposed a length of Purple "START" wire to power the coil.
That's acceptable, but now it's good that you know what's what.

The purple start wire runs from the resistor straight to the negative side of the coil and is ran on it’s own it doesn’t go through the plug in the harness.

Are you sure it's the negative side? Should be the positive side.
On an ignition coil, even though it will "work" when wired in reverse, it's not correct and not doing it's full job from what I understand. You need switched power to the positive side, and "trigger signal" (basically a ground) to the negative side.
Each time the negative side of the coil is grounded, you get a spark.

The purple start wire that is part of the plug has been rolled up and taped for some reason.

Centech provides two separate Purple/Violet START circuits. One is shorter than the other, runs directly from the ignition switch to the starter relay's S terminal. This is for use with a manual transmission.
The other is a longer one and is intended for use with the neutral safety switch on an automatic transmission.

Are you running a manual or auto trans?

The ignition is a Mallory e- spark.

That's a pretty bitchin' distributor if I remember. If it's the one I'm thinking of they released it just before I stopped working as a sales rep for them. They had the "E-Spark" and one other with a fancy name, and both were very high tech, with a built-in MAP sensor and pre-programmed spark curves.
Not sure what kind of trigger module they used, but it sure looks like a Uni-Lite type. Maybe this is not the same one I'm thinking of after all.
Does it have a built-in hose fitting for a vacuum line? Or a standard vacuum advance canister?

And there is a green red and brown wire coming out of it the green wire is hooked to the positive side of the coil and red wire is connected to the negative side of the coil along with the purple start wire.

You need to verify those locations and swap them around if it turns out to be the case.
The Green wire is the trigger and should be on the negative post.
The Purple and Red are 12v switched and should be on the positive post.

Brown wire is attached to the block with negative terminal coming off battery.

Must be a ground then, and must be correct or it would not work in theory.
But it would not hurt to find a wiring diagram just to be sure.

Why would there be a separate purple wire that is ran straight from the resistor to the coil?

If it's straight between them, then like I mentioned above it's probably just some wire that the installer had laying around.
Because it's only connected to the resistor at one end, and only connected to the coil at the other end, then it's original START purpose as printed on it is no longer valid. It's now just a power wire for the coil.
But again, it should be on the positive side of the coil.

Looks like I’ve got a mess here but it ran like this for the past year and a half I’ve had it and haven’t touched or switched any of the wires

It is a mess. But hey, like you said, it worked!;D
The good thing is wires don't care how they are routed, as long as they begin and end in the correct place. Everything else is just cosmetics, unless it's routed in such a way as to be dangerous. Such as when up against a moving part for example.

Glad it's running now!

Paul

 

[DirtDonk]

Well, it was a fuse.. I had checked the ignition fuse but the alt/emm fuse was bad...

Maybe that's normal, or maybe it means that the installer used a different circuit to power the ignition.
I guess it depends on how Centech has their wires assembled at the fuse panel.

Paul