Not getting 12 volts to coil
I'll double check but pretty sure both the 1985 SJ Service manual and SUN
s VAT 40 manual consider starting voltage down to 9 or 9.5 Volts acceptable. Not great or even good, but OK. Also its very important to fully charge the battery before testing.
Based on your description*, it sounds like you are describing the drop in battery's output voltage when during start. This is due to the large draw from the solenoid and starter motor.
To determine this; Measure the the voltage across the battery terminals during start.
To find out if there is a "drop on the positive path"; take additional measurements at the same time at other locations along the current path.
*description
**When the key is in start position, the switch only connects the feed in (J1) to the two circuits labeled Start and Starter.
With the key in Start position, any current flowing through the alternator field will have to go through the ballast resistor. That will naturally cause a voltage drop.
However since there are other easier paths to ground, hardly any current may flow through the resistor. In that case the voltage on both sides of the resistor will be the same.
Fully illustrated sequence of current flow for a Mopar starting sequence in this post. Bump Switch
I'll double check but pretty sure both the 1985 SJ Service manual and SUN
s VAT 40 manual consider starting voltage down to 9 or 9.5 Volts acceptable. Not great or even good, but OK. Also its very important to fully charge the battery before testing.
Two different things can be called 'voltage drop'.
Based on your description*, it sounds like you are describing the drop in battery's output voltage when during start. This is due to the large draw from the solenoid and starter motor.
To determine this; Measure the the voltage across the battery terminals during start.
To find out if there is a "drop on the positive path"; take additional measurements at the same time at other locations along the current path.
> There should be no measureable difference between the battery positive terminal and the alternator output stud.
> During start, there may be a difference between battery positive and the alternator's blue field wire. It's normal and not important.**
> While running, there should be only a small voltage difference between the run circuiit and the bettery positive and the alternator output terminals.
> During start, there may be a difference between battery positive and the alternator's blue field wire. It's normal and not important.**
> While running, there should be only a small voltage difference between the run circuiit and the bettery positive and the alternator output terminals.
*description
**When the key is in start position, the switch only connects the feed in (J1) to the two circuits labeled Start and Starter.
With the key in Start position, any current flowing through the alternator field will have to go through the ballast resistor. That will naturally cause a voltage drop.
However since there are other easier paths to ground, hardly any current may flow through the resistor. In that case the voltage on both sides of the resistor will be the same.
Fully illustrated sequence of current flow for a Mopar starting sequence in this post. Bump Switch
