wire with excessive resistance

[alex 18]

I believe the wire from the I terminal of the starter solenoid to the positive coil terminal has excessive resistance somewhere. Is there a way to test it and hopefully find the fault?

[LindenBruce 27]

Yes. Along the way there is a pink resistor wire in the under dash harness. If you are measuring a value through this wire you will have a lower than expected value. Let me guess it's around 9-10 volts right? B.

[alex 18]

I am seeing that value but also when the key is in the start position when, as I understand it, there should be 12V going to the coil. I am getting spark all the way the spark plugs but the engine does not catch at all. There is gas squirting from the carb. In case it matters, I have a Mallory Unlite distributor with a Mallory coil.

[LindenBruce 27]

Well, if your plugs are sparking and she still won't start you have another issue. What are the details on your engine? It could be a timing issue. have you run a compression test? Did this problem just crop up? Or is this a new install that has yet to run? B.

[Midlife 814]

Yes. Along the way there is a pink resistor wire in the under dash harness. If you are measuring a value through this wire you will have a lower than expected value. Let me guess it's around 9-10 volts right? B.

 

Not quite true. The brown wire coming from the I terminal meets up with the end of the pink resistor wire at the firewall plug. From there, a red/green wire goes to the coil. Going from the I terminal to the coil should have essentially zero resistance. The pink resistor wire has about 1.5 ohms resistance, and it starts either at the tach or the ignition, depending upon a tach or standard dash.

[alex 18]

The engine is an old 351W with a 2 barrel 2100 that has run just fine since I installed the Mallory distributor and coil over a year ago. The compression is fine.

 

I had an issue with the starter not stopping after starting the engine. I replaced the starter solenoid although I think I might have let it happen a few too many times. The car ran fine as usual after that for a few days. I drove home and the car would not shut off. Thinking it was the new starter solenoid having an issue, I tested it a few times. After the third or fourth try I tried to restart it and that was the last time the engine fired.

 

My hypothesis is that the wire from the I terminal to the coil has been damaged and cannot carry enough current to start the car.

 

Does this hypothesis sound reasonable?

[Midlife 814]

Yes, it is possible. Also, some aftermarket dizzies require a full 12V for running and if not properly set-up, can burn up the pink resistor wire. If that happens, it can damage the contact inside the molded plug where the brown and pink resistor wire meet.

[alex 18]

The Mallory is not one of them that requires 12V for running according to the installation instructions.

 

To identify where in the I terminal to coil wire the voltage is being lost, how could that be done?

[LoneWolf2U 136]

At the sol, Start by removing the starter cable (so it won't crank)and brown wire from the I post and hook up meter in its place.

Use jumper wire from sol + side to s post, Does the I post show voltage?

Yes, trace wire out to firewall connection.

No, replace sol.

 

Brown wire goes from sol I post to firewall and is bridged on to the red/grn wire to coils + side.

With starter cable still off jump sol and see if it gets voltage to coil + side.

Yes, check dist.

[alex 18]

Mach1Rider, thanks for the suggestions. The voltage at the I terminal on the solenoid shows 12.19 V when the S terminal of the solenoid is jumped.

 

The + on the coil shows 8.09 V when the S terminal is jumped. I was expecting 12 V since jumping the S terminal is the act of the starting the car and should provide 12 V to the coil.

[LoneWolf2U 136]

Voltage drop may happen with starter motor engagement.

Check grounding points.

How is voltage with cable to starter removed from sol?

Still getting a large drop in voltage?

Yes, trace wire from sol for damage or poor connection points.

[danno 128]

Mach1Rider, thanks for the suggestions. The voltage at the I terminal on the solenoid shows 12.19 V when the S terminal of the solenoid is jumped.

 

The + on the coil shows 8.09 V when the S terminal is jumped. I was expecting 12 V since jumping the S terminal is the act of the starting the car and should provide 12 V to the coil.

 

The 8.09 v is lower than it should be. Is it correct that you do not have electronic ignition? Try disconnecting your coil and see if it goes up significantly. It certainly should.

 

But back to Bruce's point, if you have spark on the plugs, it certainly does not look like an electrical problem.

[Midlife 814]

Mach1Rider, thanks for the suggestions. The voltage at the I terminal on the solenoid shows 12.19 V when the S terminal of the solenoid is jumped.

 

The + on the coil shows 8.09 V when the S terminal is jumped. I was expecting 12 V since jumping the S terminal is the act of the starting the car and should provide 12 V to the coil.

 

Repeat the test at the coil by removing the wire at the + side of the coil. Measure the voltage at the disconnected lead. If it is still 8.09V, then the wiring is bad (probably a previous owner screwed up the pink resistor wire). If it is battery voltage, then the coil itself or the ignition system is drawing the voltage down by excessive current.

[alex 18]

I did test with the wire to the coil and did get 12 V. i do have electronic ignition (Mallory Unilite distributor and a Mallory coil).

 

I had tested the Mallory coil according to their steps (

) and it did test successfully. I also tested the Mallory Unilite module (

) which also tested successfully.

 

What else am I missing?

[danno 128]

The Mallory disti must have some electronics somewhere, maybe in it? Is there an external box connected to it? Where does this box get it's operating voltage? Do you just have the one wire from the coil to the disti?

[alex 18]

The module is inside the distributor. The only other component is the coil. The distributor gets its voltage on a wire from the negative coil terminal as well as a wire from the positive coil terminal. The pdf below has a diagram on the top of page 3 that details the wiring.

 

http://prestoliteperformance.com/media/instructions/mallory/Mallory_Instructions_unilite_distributor_37_38_45_47.pdf

[alex 18]

I found some time to continue looking at this issue and noticed that the circuit that is connected to the I terminal has 12V when the key is in the run position. Disconnecting the connection from the I terminal shows that the voltage is not from the starter solenoid but instead from the ignition wiring. Should there be voltage on that circuit even in the run position? I thought that circuit only had 12V when the ignition switch was in the start position.

[Midlife 814]

The I post at the starter solenoid should be zero volts when the wire is disconnected and the key in the RUN position. When the wire is connected, you should see the same voltage as at the coil: 6.5-9V.

 

It sounds like someone may have bypassed your pink resistor wire.

[Chesterhoss 10]

I know this might have been addressed already. But i had the same prob when i picked up my 69 mach with the same 2v 351w. I had issues with the starter not cutting out, and sometimes the starter cut out prior to ignition. I changed the solenoid and shot wires as well as cleaned the grounds. It ended up being the ignition switch itself for me. The contacts were worn and weak and the retaining spring on the inside was actually creating a case ground issue. Cheap easy fix, and hope it helps man.