Alternator voltage odd readings

[vacuum 6]

With a "cold" alternator per my scan tool, the battery/alternator voltage is 13.8-14 V and same voltage reading using a MM.

Now after the alternator becomes hot the scan tool read 12.8-13.1 volts. However, MM reads 13.8-14.

Here's something else odd...with a stock incandescent dash bulb the voltage light does not illuminate. However if I use an equivalent LED bulb after the alternator becomes hot the bulb flashes.

Any help would be greatly appreciated.

 

[Backndagame]

Does it go up when you Rev the engine, and also is the bolt behind alternator loose?

Sent from my SM-N910V using Tapatalk

 

[mikestertwo]

Where are you reading the voltage with the MM? The scan tool reads voltage off the IGN circuit. That voltage will vary depending on load.

 

[pmesfun]

Check voltage at ignition switch. I had the same problem and mine was the switch.

Sent from my SM-G930P using Tapatalk

 

[vacuum 6]

Does it go up when you Rev the engine, and also is the bolt behind alternator loose?

Sent from my SM-N910V using Tapatalk

I'm assuming you're talking voltage...no.

 

[vacuum 6]

Check voltage at ignition switch. I had the same problem and mine was the switch.

Sent from my SM-G930P using Tapatalk

How and what should the voltage be?

 

[pmesfun]

PINK wire, should be close to the voltage at the battery and the RED wire too, that supplies power to the IGN switch.

 

[vacuum 6]

Great thanks but where's the pink and red wire?

 

[pmesfun]

At ignition switch.

 

[TurboTGuy]

If you need more in depth info on readings at the ignition switch, call Nick Micale at Arizona GN, well known here on TB.com.

He just went through what you are experiencing and has some good info.

 

[vacuum 6]

Here's a stupid question: So what if the voltage seen by the ECM are low (12 V)?!?

 

[pmesfun]

Check the voltage at the ECM/IGN fuse, see if it matches.

 

[vacuum 6]

Yes I'll check that.

Here's my point: assuming the injectors and ignition see the same voltage as the ECM then screw it and run a hot wire kit for each and be done.

 

[pmesfun]

 

[pmesfun]

You could but I would want to know why the voltage(Injectors are powered by FP/INJ circuit) is low since the ignition switch power other circuits. You can check the CCCI fuse for good voltage and rule that out.

 

[vacuum 6]

View attachment 306012

Do you have a better copy?

 

[Chuck Leeper]

Cure the funk w/ the 30 y/o ign sw, and run the power thru a relay.

 

[gdsims231]

You have a simple voltage drop in your circuit. General rule is 0.2 volts is acceptable. Start at the beginning of the circuit and work your way to the end with each connection, component...place the negative of the multimeter on the positive of the alt. Now place the positive of the mm on the positive of the battery. The reading is the voltage drop of the circuit. Now move the test down the circuit until you find the significant drop. If there is none there then it is in your ground circuit.