Electrolysis in engine coolant

I have a 95 Suburban K2500. I have had to replace the radiator, the heater core twice, the aluminum quick connect fitting at the rear of the intake manifold ( 454 engine) and i suspect I will need to replace the rear heater core unit ( anyone know how to access it?)
A mechanic suggested I test for stray current in the coolant. I used a multi-meter and tested with the engine running and off. There is between .3 and .4 volts from the coolant to ground. Anyone run across this and have some idea had to locate the source of the voltage?

no idea how to locate the source, i know jegs has a product out that allows you to stop the electrolysis from happening. to get to the rear heater core, you have to take apart the interior on the passenger side. its pretty easy really, just take out the plastic cupholders, then the top part slides out and up. the rest of the interior is held on with screws that are now exposed. after that is outta the way you have a clear view of the heater core.

make sure you have GOOD ground straps from the body to the battery
stray current is normally caused by poor grounding of the body!!!!

I just posted in another thread regarding how the manifold quick connect deteriorated and broke off. Sounds like its made of aluminum. Are you saying that stray voltage would cause this fitting to fall apart?

As far as checking, do I just dip one lead into the coolant (the other to the block)?

Then what do I check for regarding proper grounding of the battery?

Current in the coolant can be caused by a bad ground but it is also normal to a smaller extent. Anytime to place two types of metal (cast iron/aluminium) ina corrosive liquid you have created a basic battery. Most people do not like DEXCOOL but this problem is one of the things it was designed to cure. Do you change your coolant regularly? Not doing so will greatly increase this effect as the coolant grows more and more acidic as time goes on. The process of electrolisys will eat at what ever metals are involved in the reaction.

other posts on this already but to be clear the fitting I referred to was made of "pot metal" whatever that is but its not magnetic. The one I replaced it with is made of steel. I wonder if the old fitting was designed before the switch to Dexcool. Obviously the coolant ate through it after 60K miles.