Suspect Firewall connection block.

[D67Cuda]

I am trying to install an MSD ready-to-run distributor and ignition wires on my 67 Barracuda. Before installing it though I ran some voltage tests. My battery puts out 12.6 volts, a wire off the ignition switch fuse is only returning 10.5 volts back to the engine compartment. The coil positive terminal only read 4.6 volts (after the ballast resistor.) I've inspected the firewall connector block tried to clean the individual terminals, but that'e not helped much. Does anyone make a replacement firewall connection block? Is there an after-market connection black that would work? Before I bother installing the MSD system, I've got to get better, more consistent voltage into the dash and back out to the engine compartment.

 

[RustyRatRod]

Have you back traced TO the firewall connector to verify that's where the voltage drop is? I'm not disagreeing that might be it, but it'd kinda suck to do all that work and still have the same problem. Have you checked all of the grounds to assure they are clean and tight?

 

[Dana67Dart]

The coil positive terminal only read 4.6 volts

I'm surprised you saw a voltage drop after the ballast resister. Disconnect the coil and test again.

The ballast will show a voltage drop with a load.

Also other places will show a voltage drop with a load.

2.5v is a lot

I would suspect the connector on the ignition switch.

The terminal block on the firewall is reproduced, as are the separate connectors and the individual terminals.

Pull the ignition switch and inspect the connector.

 

[Mattax]

A. There is no fuse on the ignition circuit.
B. Amount of voltage drop depends on both resistance and flow.
Resistance x flow = Voltage drop
You can't check for resistance without knowing how much current is being pulled and the route the current is taking.
Also measuring to ground can be misleading. Its good to know the voltage available at the power source but measure the votlage differnece directly when possible.

 

[Mattax]

Just to be clear, flow is electrons moving. Voltage is potential energy.
For example, this shows current flow immediately after starting. The power source is the alternator. The ignition, alternator's rotor, and the battery are drawing power through the paths shown.

If the alternator is producing power at 14 Volts, then it is 14 Volts everywhere except where current flows through resistance.

With the engine off, power is coming from the battery if something is turned on. Otherwise there is voltage in everything connected to the battery, but no flow, so resistance has no effect on the voltage. Voltage in that case just shows items are connected.
Knowing the flow path and the approximate current, we can then diagnose using differences in voltage.

67 Dart Conv. - No Tail Lights, Park Lights, Flashers

Both connectors? yes

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Voltage Problem

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?

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