Hey guys my 79 F150 dies everytime a tiny bit of water splashes on my alternator. I pulled the 2 slip on plugs off the back and filled them with dielectric grease and put them back on. the third wire is a bolt on (its a pos wire) I just left it the way it is. the rubber cover on that one is broken off. do you think thats what makes it die??? Also after I pulled off the 2 slip on plugs it didnt want to charge right. Anyone know how to seal the back of the alt so it doesnt stall everytime I hit a mud hole??? Also anyone know where to get a good higher amp alt for cheap??? My stock 60 amp doesnt do well pushing my electric fans and lights.

 

This very well could be the problem.

 

That truck can run without the alternator as long as the battery is good. The entire thing can be gone, and it will run. Perhaps a little water will cause a no charge problem, but as far as killing the engine, I beleive that there is something else in the equation that is causing the engine to die.

 

If enough water shorts the battery connection on the alternator down to ground, it will kill the motor because the battery voltage will be pulled very low, which will cut power to the module and coil.

 

Ive run these thing under water and mud. I mean totally submerged without this occuring. I have a alternator disconnect to prevent it from running when it is submerged, but I have mever had such a discharge problem.
OP states that only a tiny bit of water makes this happen. It would require enough water and regular water does not conduct enough electricity to ground out the battery at such a rate that the bettery will become depleated of all electrical power.

Drop a 12VDC battery in a tub of water and see how long it takes to drain the battery. It takes forever. I use a similar method (electrloysis) and car batteries to remove rust and generally clean parts. The positive and negative leads are submerged into a liquid bath with salt or soda added to increase the conductivity of the water as plain water alone is not enough.
Small amounts of water splashing on bare leads of an alternator is not going to cause enough resistance to drain a battery to the point that the engine dies.

Something else is the problem here. If the battery is charging from the alternator, then the small amount of water is getting into something else, like the dizzy.

 

We are claiming two different points. Nothing you have said is incorrect.

I am not saying it drains the battery. What I am saying, is the electronics in the ignition module require a certain voltage threshold in order to operate. If a strong enough load is placed on the battery (like a short), enough current flows through the battery's internal resistance such that the effective battery voltage is less than the minimum supply voltage for the module. This is due to the voltage drop across the internal resistance of the battery. If this occurs, the module will stop firing the coil, and the motor will cut out.

The battery doesn't have to be completely depleted for this to happen, such that the voltage between the two terminals is zero. This can happen if the effective battery voltage drops several volts. This does not necessarily drain the battery. As soon as the short is removed, the battery is capable of supplying normal current if the charge removed was minimal. I've had this happen when some wiring melted to my headers.

Now the question becomes whether or not water is enough of a conductor for this to happen. I filled a cup with water and measured the resistance, and after seeing the results I'm shifting my view and agreeing with you; I don't think it's enough current draw for either case to happen because the resistance was pretty high. It's possible however that water is being drawn into the intake or getting into the distributor.

My guess was incorrect; I apologize for the confusion. Thank you for the insight 75F350.

 

I dont think it was incorrect, after reading, I was in a position to agree with you and I think you have me convinced.
The variable would be the conductivity of the water that the alternator is being subjected to, and it would have to have something added to create better conductivity, but in regions where salt is added to the roads this might have an effect on this scenario.
I was leaning on the fact that plain water would not have enough condictivity to support a fault in the module, but if the addition of the highly conductive salt were to be added, this theory would hole water (pun intended)
I beleieve this to be a good coversation and I perhaps was the one that confused the issue.
Together with a great discussion, we have looked at a few variables and perhaps the OP can find a resonable solution for this problem.
Thats what makes this type of participation so fun.
Thank you fmc400 for your valued insight, and ability to consider all posibilities.

 

That's a good idea about the salt, interesting thought. And thanks for the kind words.