Vehicle Electronics Question (Snowplow Related) - PeachParts Mercedes-Benz Forum

SwampYankee · #1 11-26-2008, 03:18 PM

Among my many areas of incompetence, automotive electronics is right up there near the top.

Ignoring the old adage of "If it ain't broke..." I replaced the leaking but functional lift cylinder on my plow with a new one that had a foot welded on it (used to hold the plow up when not on the vehicle, the old one had a removeable foot that used a clevis pin to hold it in place). I decided to change the fluid as well since I drained a good amount out swapping the cylinder.

I got everything hooked back up and proceeded to raise and lower and cycle left and right to bleed any air out of the system and everything was working ok. I then tried to raise the plow completely only to discover that the foot extended a fraction of an inch enough to bind up on the truck side of the mount and wouldn't budge. At that point I lost power to the plow completely and no longer could hear the solenoid clicking when pushing controls.

I figured it was easy enough to just swap out the solenoid as that must have been the problem. But to no avail. I still am not getting any power out of the solenoid to the plow (and don't hear it clicking). The replacement solenoid is a different model and I installed it visually the same way as the old one. Could it be backwards? Is there a way to test it to see if it's good? I don't have any blown fuses.

Angel · #2 11-27-2008, 08:59 PM

99% of solenoids will click when they get move, so if you still arent hearing it, its one of 2 things:

1) the slug is physically stuck/jammed
2) The solenoid isnt getting electricity.

I'd go down the electricity path first, you might need a helper to hold the "raise" button down when you are putting a voltmeter on the leads to the solenoid.

Another common automotive mistake is not using an ohmmeter to check fuses - I've seen a few myself that looked "not blown" (even with my youthful eyes) but when you take a meter to them - they show an open.

Hope this helps.

-John

mpolli · #3 11-27-2008, 10:32 PM

What he said, check the voltage at the solenoid with the solenoid connected. You could also just apply 12v directly from a battery and see of the coil operates. I don't know how often coils fail. I work on the electronics side not the hydraulics side. Assuming you have a switch type control, the fuse could be bad as was said, a connection could be bad and the switch could be bad, they can wear out. I don't know if the coils have a polarity, if so then it should be marked.

It seems strange that it failed when the plow binded up since the electronics would have to "knowledge" of that. Assuming that your hydraulic pressure is not generated with an electric pump.

SwampYankee · #4 11-28-2008, 09:50 AM

Thanks guys, I'll check that today. It's supposed to get into the 50's. It is an electro-hydraulic plow pump, albeit a very primitive one (Pathfinder Plows out of RI).

A jumper wire from the battery to the solenoid would seem to be the easiest place to start and I'll go from there.

mgburg · #5 11-28-2008, 12:53 PM

Swamp:

Check one other thing...a "fuseable link" - this is nothing more than a piece of wire, about a few guages smaller than the hot lead, spliced in series with the power lead...too much current is drawn and "POOF!" --- no power feeding the system...and the fuse in the truck may still be good, but no power to the solenoid. And, they are, sometimes, hard to find...just run your hand up and down the main power lead and feel for any distortion or bulges in the wire...then, take a needle or pin and carefully poke into the wire on either side of the bulge...measure for voltage at that point to ground...got voltage on one side and not on the other? BINGO! You've found the bad spot.

Now, cut out the dead area, splice back in a FUSE that is rated for the component you're suppose to be protecting and get rid of that "po-boy's" fuse...

mpolli · #6 11-28-2008, 03:37 PM

Post a schematic of the system if you have one. I am guessing that when the plow got hung up the current to the pump went up and something inline went "bad" (switch, fuse, wire, connector, etc.) But it is hard to say without knowing how it is wired.

SwampYankee · #7 11-28-2008, 05:30 PM

Quote:

Originally Posted by mpolli

Post a schematic of the system if you have one. I am guessing that when the plow got hung up the current to the pump went up and something inline went "bad" (switch, fuse, wire, connector, etc.) But it is hard to say without knowing how it is wired.

You are correct, sir!

OK, let me start by saying everything is back and fully functional. Thank you all for the advice and the leads.

I tested everything, both correctly and incorrectly in case I missed something or misread my multimeter. I jumped the solenoid directly with a jump wire to the battery and it worked. Son of a b!tch? What the hell is wrong with this f'n thing???

As I sat in the driver's seat, stewing and chugging a Long Trail Hibernator Ale a little light bulb went off and I wondered to myself whether or not the cigarette lighter worked. I pushed it in and nothing. I checked the fuse and sure as $h!t is was blown. I replaced the fuse, pushed the plow control to the "UP" position and sure enough the freakin' solenoid clicked to life. The plow dealer wired the Jeep up when I bought it and nowhere on the schematic is there a fuse shown on the control side (the schematic, like the plow, is very primative-hand drawn and not easily read to a clueless schmuck). Not knowing much about electronics it never dawned on me that it was because it was wired into the lighter/accessory circuit and used that fuse.

I can't tell you how embarassed, yet relieved, I was.

There are no stupid questions, just some stupid backyard mechanics.

Thanks again. If I hadn't gone through your ideas, systematically ruling out problem areas I never would have gotten to the final hangup.

And with snowplows, like everything else, you get what you pay for!