Less than 12V on VR Input w/pics

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Fittrjoe

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67 Barracuda with New Alternator but slightly overcharging 14.5-15.1
I think I know why.
VR input is 11.08 when Batt is 12.56 , key on.
Key off is .32
Added a few nice grounds from Batt to fender and Alt to fender recently per advice of a friend FYI
Shouldn’t Input wire on VR be same as Batt?
What’s the fix?

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Last edited:
Fittrjoe said:
VR input is 11.8 when Batt is 12.56 ,
Click to expand...
11.08 vs 12.56 is a 1.5v Voltage drop

Is that with the engine running or off?

That's a lot.

Check...

The bulkhead connectors are clean and tight.

The ignition switch connectors and terminals are clean and tight.

You should check it with the engine running
 
I have written hundreds on this. Maybe more. Voltage drop in the harness, terminals/ connectors and switch, and sometimes the ground circuit

To check, turn key to "run" engine stopped. Stab one probe into the top of the POS battery post and the other as close to the VR IGN terminal as you can get. Or connect to the "key" side of the ballast resistor. You are hoping for a very low reading, the lower the better. anything over about .3V (3/10 of 1 volt) you need to chase it down. Culprits are any connections, the bulkhead connector terminals for the big red and big black ammeter circuit, and the dark blue "Ign1" "run" line. Also the ignition switch connector and the switch contacts themselves

One way around that is to electrically cut the "IGN1" run wire where it comes into the engine bay, use the firewall end to trigger a relay, feed the relay off the starter relay "big stud" and run the engine bay end of the run wire to the switched contact.

GROUND: Make this test with engine running fast to simulate low/ medium cruise RPM, and first with all accessories off, and again with them on, heater, lights, etc

Stab one probe of you meter into the top of the NEG battery post, and the other hard into the mounting flange of the VR. Again, the lower, the better, zero is perfect
 
Whatever drop you measure in the harness from the battery + to the VR IGN (EG 1.5) will be ADDED to a properly working VR, AKA 13.8 + 1.5 the battery will see 15.3

Whatever you measure in the ground test will be added to THAT
 
Dana67Dart said:
11.08 vs 12.56 is a 1.5v Voltage drop

Is that with the engine running or off?

That's a lot.

Check...

The bulkhead connectors are clean and tight.

The ignition switch connectors and terminals are clean and tight.

You should check it with the engine running
Click to expand...
Off/ ignition on
 
67Dart273 said:
I have written hundreds on this. Maybe more. Voltage drop in the harness, terminals/ connectors and switch, and sometimes the ground circuit

To check, turn key to "run" engine stopped. Stab one probe into the top of the POS battery post and the other as close to the VR IGN terminal as you can get. Or connect to the "key" side of the ballast resistor. You are hoping for a very low reading, the lower the better. anything over about .3V (3/10 of 1 volt) you need to chase it down. Culprits are any connections, the bulkhead connector terminals for the big red and big black ammeter circuit, and the dark blue "Ign1" "run" line. Also the ignition switch connector and the switch contacts themselves

One way around that is to electrically cut the "IGN1" run wire where it comes into the engine bay, use the firewall end to trigger a relay, feed the relay off the starter relay "big stud" and run the engine bay end of the run wire to the switched contact.

GROUND: Make this test with engine running fast to simulate low/ medium cruise RPM, and first with all accessories off, and again with them on, heater, lights, etc

Stab one probe of you meter into the top of the NEG battery post, and the other hard into the mounting flange of the VR. Again, the lower, the better, zero is perfect
Click to expand...
Thanks for this detailed reply sir
 
Dana67Dart said:
11.08 vs 12.56 is a 1.5v Voltage drop

Is that with the engine running or off?

That's a lot.

Check...

The bulkhead connectors are clean and tight.

The ignition switch connectors and terminals are clean and tight.

You should check it with the engine running
Click to expand...
Thanks for these tips
Checked with engine running and although a moving target … averaging about the same as off - 1.5v differential
 
Dana67Dart said:
11.08 vs 12.56 is a 1.5v Voltage drop

Is that with the engine running or off?

That's a lot.

Check...

The bulkhead connectors are clean and tight.

The ignition switch connectors and terminals are clean and tight.

You should check it with the engine running
Click to expand...
Sorry to be a newbie but ignition switch as in inside the vehicle where the key inserts
Thanks !
 
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