I keep hearing this term brought up in multiple threads, but can't figure out what this is supposed to look like on the actual truck. I'm getting drivers side headlight and running light, but no passenger side. Does the switch from 24 to 12 happen at a solenoid or switch, or just wired from the batteries that way? I can't read electrical prints worth a darn. Also, tail lights are not connected right now. Does that affect the function of the front lights? Thanks for any help.
24v to 12v center tap
- Thread starter Mud taxi
- Start date
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The voltage across either battery is 12v.
The two batteries are in series, so the total voltage is 24v.
The negative side of the first battery is tied to the chassis so we use this as the zero volt reference.
The centre tap is just a wire connected to the positive side of the first battery which gives you 12v.
This has nothing to do with your headlight problem though. You probably have a dirty connector or a bad ground on the passenger side.
Can you flash your high beam on both sides?
The two batteries are in series, so the total voltage is 24v.
The negative side of the first battery is tied to the chassis so we use this as the zero volt reference.
The centre tap is just a wire connected to the positive side of the first battery which gives you 12v.
This has nothing to do with your headlight problem though. You probably have a dirty connector or a bad ground on the passenger side.
Can you flash your high beam on both sides?
- Thread starter
- #3
I'm not getting a functioning high beam on either. But the reason this is so confusing is the fact that my 12v side only has the two main cables (chassis ground and positive to negative on other battery). I would think it would need a smaller wire connected to the first battery to power the light as I think you're saying. Oddly when I meter the connector for the light I'm getting a pin reading 12v, but the light isn't on. Brand new light btw.
I don't know which year and model you have but the manual shows everything running at 24V - see attached.
What exactly are you measuring? Across the connector pins, or from the battery ground?
Could be a bad ground if the latter
What exactly are you measuring? Across the connector pins, or from the battery ground?
Could be a bad ground if the latter
- Thread starter
- #5
Canadian market 1981 bj42 (12v headlights with all other electronics being 24v) I am getting 12v out of one of the headlight connector pins, but the light still isn't functioning. I'm thinking it must be a grounding issue. My main question is; should the headlight have an isolated ground directly back to a battery, or should it be using the chassis ground? I believe my lights are powered by the 2nd battery (24v side) so if it is a chassis ground would I not be getting 24v to the light? The chassis ground is on the 12v side.
- Thread starter
- #6
And to clarify, it should only be 12v to the headlight and not 24v as far as I'm aware.
I guess it's possible that someone added a potential divider (a pair of resistors across the 24v, which gives 12v in the middle) - this wouldn't be able to power the headlights though ( just enough for a small signal 12v like maybe an instrument perhaps? )
If the feed for the lights is at 24v then the negative side would need to be 12v (not chassis) but since you only have the thick linking cable between the batteries, that seems unlikely (also very unusual way to do it - do
you have the correct worrying diagram?
I don't have my manual with me right now, and the coolerman link is broken for your year. There's a very fuzzy one I found that confirms your ground is chassis, and the 12v feed is from the first battery positive terminal.
Maybe some photos of your setup will help?
Maybe some photos of your setup will help?
jim land
SILVER Star
Factory set up on my 84 bj42 is connected to the negative post of the driver side battery , beige wire to black to red with a black strip
- Thread starter
- #11
Thanks everyone for your posts. They've been helpful, but still no luck. Everything seems to be wired correctly to me... I'm using a 1981 bj42 cad market electrical diagram for reference. I've taken the dimmer relay apart and it is functioning correctly. (Contactors for high and low beams work) and I've also taken apart and cleaned the headlight switch. My question now becomes, what kind of voltage should the dimmer relay be getting through the connector in different conditions (ie. When headlights are on/off, high beams are on/off etc.)? Any other ideas? I've also cleaned and replaced chassis ground strap. Kind of out of ideas at this point. One interesting observation; every contact I've probed so far (dimmer relay connector, and headlight connectors) are either 0v or 12v. Nothing 24v that I've measured.
Well 0 could mean the wire is broken or there is corrosion built up under the insulation at connectors. Having voltage is one thing but to do work you need amps. So even if you got voltage doesn't mean everything is good. Have you load tested the battery? lately.
jim land
SILVER Star
Did you try swapping headlight side to side , even new one could be bad
