Mf 1749 electrical issue

[iamcanadian]

Hey guys, new here. Im working on a MF 1749 and have quite the odd electrical issue. Its a friends tractor. Last year he hit a stump clearing snow and lost all lights, horn and hazard lights. He's more concerned with getting the hazards back as they are required by local laws. Switch is good, power in and out. Power to the relay. Now the kicker is when we activate the hazards the input power also pulses, as does the power at all the fuses in fuse box. Lights dont come on. Grounds check out. Replaced the relay for the hazards with same results.

 

[iamcanadian]

Correction, they had just stopped working. When he hit the stump they started working again for a day or 2 then stopped again

 

[jaxs]

I have a nagging suspicion that after grappling with this for a while,you'll find out he "FIXED IT"before he asked you to figure out what's wrong. Run a hot jumper to hazards to be certain bulbs are good. I realize you said"grounds check out"but that's what they all say.:laughing: Let's start with a couple of trials. There's normally a schematic printed on relays. Find relay coil ground and put a jumper from it to battery - post. If that does the trick,re-do ground to relay coil. A second trial is turn hazards on then clamp a booster cable or jumper wire to - battery post then to each fender and hazard light housing while watching for change. What we are looking for is poor contact between fender and engine/transmission. If Something is in series,it can be + or -.

 

[iamcanadian]

I have a nagging suspicion that after grappling with this for a while,you'll find out he "FIXED IT"before he asked you to figure out what's wrong. Run a hot jumper to hazards to be certain bulbs are good. I realize you said"grounds check out"but that's what they all say.:laughing: Let's start with a couple of trials. There's normally a schematic printed on relays. Find relay coil ground and put a jumper from it to battery - post. If that does the trick,re-do ground to relay coil. A second trial is turn hazards on then clamp a booster cable or jumper wire to - battery post then to each fender and hazard light housing while watching for change. What we are looking for is poor contact between fender and engine/transmission. If Something is in series,it can be + or -.

I did the trials with bulbs, they work that way. Theres no diagram on the hazard relay. When doing the same trials with headlights it got really odd. Direct power to bulbs-good. Back up to the headlight relays , i got the hot 12v on the nomally open contact, jumper the coil and the voltage drops to 6-7 and no lights, if i put a direct hot from battery to the other side of the normally open contact (the one that goes to the bulbs) the lights come work. Could the multifunction switch on the steering column cause this if its faulty? It appears to be faulty. Ive got the 12v going into it. No output on any pin when cycling functions, checked for continuity and have none either when cycling light functions. Ive got no diagram so im in it blind lol.

 

[jaxs]

Parts nomenclature will confuse things if we aren't carful. That voltage drop sound's like something in series that shouldn't be. Are you saying that you ran 12v hot from battery to relay post that is supposed to be hot all the time,then closed the contact? That would eliminate wires and switches before relay as the culprit. When you say "jumper the coil and the voltage drop's to 6-7",is that the electro-maganet coil that close's relay contact? There is supposed to be voltage drop across that coil but that voltage doesn't supply power to anything else. Be certain that coil isn't in series with lights.

 

[iamcanadian]

Ya call the coil pins a1 and a2 and contact pins 1 and 2. Say its 2 thats always hot and 1 goes to the lights. I ran a hot to 1 and lights turn on. I removed that hot i ran. Now say a1 is + and a2 is -. I put my hot battery jumper to a1 to activate the relay coil. When i do this the voltage on pin 2 drops.

 

[jaxs]

While checking volts at pin 2,be sure to touch black meter lead to - post on battery or engine block,NOT a2 . I think a wireing diagram will be the easiest way to cure this. Schematics should be available for a tractor no older than this. Ask around to see if a dealer will copy the light diagram from their shop manual. Based on what you said in post#6,there almost has to be a resistive device, a poor connection or another relay on pin 2 wire upstream from the relay you are testing. Why I say that is because the measured 12v would have to be disconnected when the lesser volts are applied to pin 2. Stated another way. If while 12 volts were being applied to pin 2,you applied 7 or 8 volts,the voltage would remain 12. That being true,the 12v is being disconnected when the relay being tested closes. If owner's manual say's key must be on before lights will function,instead of supplying 12v to fuses 12v might be supplied to a relay that in turn send's 12v to fuses. The factory might do that so a lighter duty ignition switch could be used to save a few $. I have a suggestion. Same as you did in post 6, put hot battery jumper to a1 to activate the relay coil. Working backwards toward battery,follow wire from pin 2 through connections and devices until you find where it drops from 12v to 7v. If due to insulation on wire you can't take a read with meter,push a straight pin through insulation. There is a point where voltage drops,find it.