102A3 Headlight issues!

[Busted Knuckle]

Hello MCI wiring guru's,
Hey have any of you had it where only the bright head lights will work? We have changed out the relay for the high/low, and we have swapped for a known good dimmer switch, dad has done extensive schematic tracing and voltage ohms testing and we still can't figure it out! nothing on dim & all 4 on high! (PS I thought I'd be smart and just unplug the center high beems which promptly caused the outside 2 to blow!) Confused and in desperate need of someone who understands the way these things work! Call dad (Gene) or I with any Ideas 731-885-7460 as I am heading back to the shop to work on it somemore as soon I send this post!   BK 

[Sammy]

Hey BK, I only have a diagram for a D model here at home- 1993.
Can you send me a copy of your schematic?
I'm not sure if your headlights are like a MC-9 - they work on a voltage drop principle. It will  have 24 v on 1 side as a feed, 12 volts on the other end, a voltage drop of 12 volts across the bulbs - that's what makes your headlights work - low beam anyway.
I'm off today - mental health day, lol...and I'm going over to the shop in a bit.
I'll see what I can find for you. Gimme a call if you need a hand. 
Sammy

[buswarrior]

Off the top of my head, I'd wonder if the centre tap is fouled up, and you are running 24 volts through where there's supposed to be 12v?

12 volt headlights running on a 24 volt system are wired like the two hot legs in your house give you 120/240.

Centre tap between the sides only has current if a bulb blows, otherwise current runs through both headlights and back to the batteries, each headlight sees half of the 24v.

The centre tap and the hot have to be switched as one. Maybe the relay is bad, wire broken, or something has been disconnected unintentionally?

happy coaching!
buswarrior

[Busted Knuckle]

Hi BW,
And we wondered about that too, but we never disconnected anything when this problem started. We copied a schematic from our manual and ran it down best we could. Also dad checked resistance and voltages everywhere. Finally did find a couple wires that had been hot and sorta stuck together (but can't say for sure they were shorting or not). Last I know when he left at 2 AM on Monday he had 2 and a half (one bright very dim on the right) on dim and 4 very bright on bright. He hasn't called and complained or asked for any help or suggestions since then so I guess it's still the same or fixed itself. Thanks for the thoughts from you and Sammy both!   BK