Super 88 starter

You have voltage drop somewhere in the circuit. You said that you have 6 Volts at the terminal on the starter switch post coming from the battery. You could have 6 V. without a load and have a nothing under load. Start at one end of the circuit, perferably at the battery. Take your voltmeter and put one pin on the battery post and other on the cable. Engage the starter for a load. Now read your voltmeter. You should not have more than .05 Volt reading on your meter. Proceed through the complete circuit one component to the next at a time. When you find the connection that reads near 6 Volts you have found the problem. If the starter is grounded internally, it will drag the battery voltage down to near 2 Volt. If the starter is internally grounded and you hold the starter engaged for any length of time, the cable should get hot.