headlight problem 78bj40 (1 Viewer)

mike

82bj42 1st project
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I'm getting power to the drivers side headlight only,the passenger side headlight isn't getting any power at the 3-prong connector behind the headlight. Could this be a headlight switch problem? Any advise or suggestions would be appreaciated. Thx inadvance
 
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mike said:
I'm getting power to the drivers side headlight only,the passenger side headlight isn't getting any power at the 3-prong connector behind the headlight. Could this be a headlight switch problem? Any advise or suggestions would be appreaciated. Thx inadvance
Start with this, then report back what a volt meter says for each female connector on each side: https://forum.ih8mud.com/showthread.php?t=68379

hth's

gb
 

mike

82bj42 1st project
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Greg,
This is what I get
with the lights off,
Passenger side all three pins have 12 volts power
Drivers side all three pins have no power

With the lights on low beam,
passenger side--all three pins have 12 volts power
driver side 11.84 volts at low beam pin, the other two pins have .22volts


With lights on high beam,
Passenger side--all three plugs have 12volts of power
Drivers side-- high beam pin has 12volts, the other two pins have .3 volts

Drivers side headlight works on both high and low beam, passenger side does not work at all.
WhAt do you think is causing this problem? Thx
 
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I just had a problem with my driver's headlight coming on spontaneously after it rained. After some fiddling with the dimmer relay, the driver light wouldn't come on for low beam but would for high beam. I found one of the contacts in the dimmer relay was actually contacting when it shouldn't--that killed the driver light on low beam. This evil center tap thing is truly funky because you actually need certain contacts in the relay to be open for the light to be on.

I don't think I can explain anything further than to say you might consider pulling down your dimmer relay, pulling off the metal cover, plug it back into the wiring harness, turn the lights off and on, high beam-low beam, watch the relay in action, and do some trial and error with the contacts. That's all I did. Not very scientific but it worked for me.

The dimmer relay is up under the dash just to the right of the steering column (on my 42 at least). You can find it also by listening as you turn the lights on and off or hitting the high beams etc.

I'm sure you have, but have you tried switching headlights to make sure it's not your headlight?

HTH
B
 
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Have you checked the 15A fuse? If it's like my 78', the LH is powered off the fusible link (12V), and the RH is powered off the fuse box (24V).

Since your LH is working, it seams like your dimmer relay is working correctly. My relay is a 12V, powered from the fusible link.

Also check to see you are getting 24V to the dimmer relay from the fuse.
 
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Good ideas all.

Fuse or dimmer relay would be the two spots to check right away. If they check out...maybe getting into the wiring is your next step.

gb
 

mike

82bj42 1st project
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Corvalis, Greg,
Where is that 12 volt fusible link located on a 78 bj40 and what dose it look like?
All the fuses are good.
Thx
 
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mike said:
Corvalis, Greg,
Where is that 12 volt fusible link located on a 78 bj40 and what dose it look like?
All the fuses are good.
Thx
On the high side battery there will be a single wire coming off the negative pole, to a connector. This wire goes under the rad with the horn wires, joins some other harness wires on the right fender, then heads into the firewall, to the headlight relay (above the pedals). The 24V lead comes into the relay from the fuse panel on the left.

RIGHT SIDE - Strange all three headlight connections show 12V on the right side. There should only be two showing 12V when the headlights are off. The left side is the side that runs high or low as 24V, with 12V neutral. Your 24V is not getting routed correctly to this side it seems.

LEFT SIDE - Seems to be working correctly, as this is the 12V light with 0V neutral. There is a feed somewhere in your system causing the reading on the .22V, but perhaps it will sort itself out when you find the issue.

Is this vehicle new to you? Perhaps someone has been into the headlight wiring and mucked things up?

Is there someone near you with a BJ40, that would let you borrow their headlight relay?

Can you please use left side and right side. I have RHD and LHD vehicles and get easily confused when you say "drivers side" and passanger side".

Thanks and hth's

gb
 

mike

82bj42 1st project
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Greg,
I swaped the headlight dimmer relay with another one, I still have the same problem. I can hear both relays clicking on and off. What should I be checking next?
This is a new vehicle to me, I'm not really sure what the former owner had done--if anything? Thx
 
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Did you find the fusible link?

It's gotta be in the wiring but gosh having the 12 volts on all pins in the pass side/RH light really looks like you've got some closed contacts in the relay.

Can you follow the wires and see if they've been hacked into? My wires were hacked but fortunately they seem to work...

B
 
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Diescipel said:
Did you find the fusible link?

It's gotta be in the wiring but gosh having the 12 volts on all pins in the pass side/RH light really looks like you've got some closed contacts in the relay.

Can you follow the wires and see if they've been hacked into? My wires were hacked but fortunately they seem to work...

B
I guess I did not explain where the fuseable link was: It is just after the center tap on the highside battery negative pole. I think it is before the connector.

Where do you go next? Strange one, and electrical trouble shooting is no fun. If you have tried another relay that is in known good condition, if the 24v fuse for the headlight, and the 12V fuseable link are good...unless I am missing something obvious, then it is into the harness to see if this shows anything. When I pull the wires out of the harness on the right side fender I found my problem right away. A PO had cut all the 24V wires, and fed the headlights 12V. This of course caused a battery imbalance.

Here are my results with color codes for the 1981 BJ42. I tried to draw the pins, and mark the wire colors beside the pins, but that did not work, so go into the text to see what wire should show what voltage.

http://www.birfield.com/modules.php?name=Archives&p=/archives/html/dtlc/2001-07/msg00132.html

hth's

gb
 
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Mike did you ever solve this issue? I have a '79 BJ40 with the 24V system and the 12V center-tap lights just like yours, and mine is doing the exact same thing yours is. I have drivers side headlight functioning fine... My passenger side does not work at all and reads 12V on all 3 light pins all the time. What did you do to resolve this? My dimmer relay has been checked and is fine. My fuse in the fuse panel is fine. My centertap fuse is also fine. Could this be a problem with my light switch, or high/low beam switch, or high beam light on my dash (which is either not working or burnt out). Help!
 
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It's gotta be a switch. I've got proper input voltage everywhere but the wrong voltage at the RH headlight. All the harnesses test fine and grounded properly also.
 
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Need some help guys... I've got a '79 BJ40 24v cdn model with the 12v centertap headlights.
I've got the drivers side headlight operating fine.
Nothing at all from the passenger headlight.
Tested the voltage at the passenger bulb with the bulb unplugged and it measures exactly the same as the drivers side both off, low beam, and high beam.
However, when the passenger bulb (checked, works!) gets plugged back in, I get zero volts on high beam and low beam leads.
Where is the +12v disappearing to on this passenger bulb once the bulb is present in the circuit?
The drivers bulb always works fine low and high regardless.
Tested the switch, relay(dimmer), wiring harness, different bulbs - all test ok.
WTF is going on??? Any ideas??
Thx! Driving me crazy...
 
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Wait a minute. I should have 24v at the drivers side light. Ah ha. I only have 12v. So the 12 is cancelling itself out resulting in zero. So why do I not have 24v coming out of my relay dimmer to my drivers side light? My dimmer tests fine and has 24v coming into it ok.
?!
 

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