UPDATE:
Ok here's how it all panned out - the culprit turned out to be a bad electrical pump motor! Here's what really grinds me, usually I do most of my own mechanic work. I didn't have the time to work on this particular vehicle so I'd taken it to a couple mechanics that I respected. It's been a chronic problem truck for snow - but runs great for landscaping.
Anyway, last year I had the alternator replaced ($180) while we were putting a heavy duty radiator in the truck ('92 F250) to remedy a chronic overheating problem. Earlier last year - we replaced the battery because it tested bad ($100).
Then, this year, the chronic drain on the electrical system reappeared as soon as we hooked the plow back up for winter. After the vehicle stalled during a snow storm and had to jumped twice, I took the battery in to re-check it. It was bad, but they didn't have a replacement - so I end up shelling out another $90 to get a battery so that the truck can continue its route. I took it in to have the electrical system checked later - $80. The mechanic told me everything was OK and that the driver was probably overloading the system by playing the radio, running the heater on high and having the lights on. A week or so later, the problem reappeared and I took it back to the guy and asked him to look at it again with special attention to the plow (motor and pump) as I was sure this was the source of the problem. His solution: a new alternator $250 this time. Two days later, another snow - another stalling problem. Back to the shop - this time the guy puts a new battery in - another $100! When I asked him about the draw from the electrical motor on the pump, he assured me he tested it and the draw was normal.
Finally, sick of having to do two routes each time this truck breaks down, I take it to the Western dealer. They test the draw and its 300 Amps - twice the normal! I had big suspicions that it was either the pump or the electrical motor. But, not knowing how to test the draw and know how to isolate the problem between the pump and electrical motor if the draw was too big, I decided to take it to the experts (instead of troubleshooting it myself and risking finding out I was wrong durring the next snow storm). Here's the painful part,after nearly $800 in two years to repair the wrong things (don't treat the symptoms, treat the problem!),they charge me $140 for the electrical motor and another $165 (nearly 3 hrs labor) to put it in! What a rape - two bolts and two electrical connections - $165! That hurts - especially when I could have gotten the motor for $100 and installed it myself in 5 minutes.
Even after wasting $800 in paying these half-assed mechanics to misdiagnose and repair things that weren't the cause, I wouldn't have minded paying for a hour in labor and diagnosis. Man, time to shell out the $25 for the Weestern Mechanics Manual and install new batteries in my multi-meter!
Sorry for the long post - thought I'd let you all know how it turned out. Thanks for letting me vent.
The plow still moves a little slow - but doesn't draw nearly the amps. I was thinking of replacing the pump itself (as we've got a new one laying in the shop and I did find considerable metal shavings in the system after it ran dry once). Also thinking of taking the crossover valves out and cleaning them (never flushed/cleaned them after I found the shavings and cleaned the resevoir). Any tips on removing and cleaning these valves?
Please know - all your help and suggestions have been greated appreciated. Thanks!!!