Voltage Problem

[scatpakman]

Ok I'm having starting issues. I only have 8.5 volts at the coil. Not enough to start the car. If I run a jumper from a good 12 volt source to the coil car starts with no problem. Details include the following; MSD coil, MSD ready to run distributor. No MSD box. Any ideas on where to start?

 

[Dana67Dart]

Sounds like the IGN 2 wiring is not attached to the IGN 1.

The voltage sounds like you still have the ballast resister attached.

 

[67Dart273]

I agree, you have eliminated the ballast? WHAT YEAR are we workin on?

Essentially you must connect the wire which originally branched into the coil + wire at the ballast to the "run" wire

 

[Mattax]

Or the battery doesn't have much energy
OP: What's the battery voltage when starting?

 

[Dana67Dart]

Not enough to start the car. If I run a jumper from a good 12 volt source to the coil car starts with no problem

Or the battery doesn't have much energy
OP: What's the battery voltage when starting

I think this proves the battery is ok.

Op could have everything wired correctly BUT the ignition switch could be faulty

 

[Mattax]

I think this proves the battery is ok.

Op could have everything wired correctly BUT the ignition switch is faulty

I see your point. That's a reasonable deduction. I'd want to check if the starter drawing hte battery down to 9 Volts. And if not, where is the drop? Could be right at hte battery terminal or any place down stream there. Mechanically the switch gets teh most wear, but the engine compartment connections take the most abuse.

 

[scatpakman]

I see your point. That's a reasonable deduction. I'd want to check if the starter drawing hte battery down to 9 Volts. And if not, where is the drop? Could be right at hte battery terminal or any place down stream there. Mechanically the switch gets teh most wear, but the engine compartment connections take the most abuse.

I'm thinking it's either the ignition switch or the fuseable link that runs to the coil from the ignition. Everything else checks out as far as voltage goes.

 

[Mattax]

Clip your voltmeter's lead on at the battery positive and hit starter.
Get a reading.
if its close to 11 Volts, then yes there is a big drop.
If its 9 Volts, then the battery is the first thing to fix. A good battery should not drop that low during start.
Narrow it down by measuring voltage, or better voltage differences.
For example:
Move the probe to the junction at the relay. Hit the starter and see if the reading is significantly lower than when it was measured on the battery terminal with the starter engaged.
A direct voltage drop measurement is better when looking for drops. One probe on the supply terminal (battery positive), the other terminal on the junction of interest. In this example that's the junction at the relay. Hit the starter. The meter shows the difference in voltage.

 

[Mattax]

Fusible link on most is difficult to measure directly because the terminal at the multiconnector has a seal.

You can use voltage drop to look for resistance from the battery to the main splice without running the starter.
Hook up the meter to measure voltage drop.
Turn on the headlights
Read the current on the ammeter
Read the voltage drop on the multimeter.

The headlights & tail lights typically draw 12 to 15 amps. That's significantly more than the starting relay and ignition typically do. The ammeter readings will confirm that or show otherwise.
Lets say starting draws 5 amps through the wiring, and lights draw 15 amps.
That amplifies the effect of any resistance by 3.
Voltage drop with three times higher current will be three times larger.

Charge the battery when done testing.

 

[Mattax]

Diagram illustrating measuring voltage loss between the relay junction and the bulkhead connector.

Voltage drop by comparing voltage to ground.

If access is difficult or you don't have a long lead, a good wire that does not have current flowing in it can be used as lead extension.
For example, if the alternator's output terminal is accessible, it connects to the main splice.
With either headlights on or hitting start, measureing as illustrated below shows losses between battery positve and the mainsplice.

 

[scatpakman]

Thanks for the help Mattax! Printing the diagrams and headed out to the shop.