Overcharging16-18v

[Muddytruckin]

so I replaced my fried alt with another 65 factory type replacement and put a new voltage reg on. Car starts up and runs for about 15 secs and shuts off. During those 15 secs the voltage jumps around between 13-18v. What can cause this? This is a photo of how I have it wired up with the aftermarket wiring harness. Cars a 73 challenger so it's the late model.

 

[challenger6pak]

Do you have a ground strap from the motor to the body? Lack of one can cause the voltage regulator to misread and let too much voltage through.

 

[Muddytruckin]

Yes, have a ground cable from battery to motor and another from motor to firewall at the orange box.

 

[AUSTA]

so I replaced my fried alt with another 65 factory type replacement and put a new voltage reg on. Car starts up and runs for about 15 secs and shuts off. During those 15 secs the voltage jumps around between 13-18v. What can cause this? This is a photo of how I have it wired up with the aftermarket wiring harness. Cars a 73 challenger so it's the late model.

Do you know if the alternator is good are the slip rings clean
it sounds like a connection problem on the positive it is hard to jump from 13 straight to 18 as normally the battery would soak up the extra voltage .
Where are you measuring the 18 is it at the alternator or battery terminals

 

[Muddytruckin]

I had them bench test the new alt before I left the store with it, tested good. Positive connections are clean. I'm measuring voltage from a 12v switched power wire inside the car. Tested the same with a multimeter as the voltage gauge.

 

[challenger6pak]

What are you using to read the voltage amount? Could it be faulty?

 

[Muddytruckin]

A sunpro voltage gauge(not the best source) and I've measures it with a blue point multimeter(better than the sunpro) both gave the same readings.

 

[AUSTA]

I had them bench test the new alt before I left the store with it, tested good. Positive connections are clean. I'm measuring voltage from a 12v switched power wire inside the car. Tested the same with a multimeter as the voltage gauge.

Have you tried measuring at the battery.
Does the alternator charge wire go directly to the battery or through the firewall connector & then back
Do you have an amp gauge on the dash is it showing charge