lowenbrau
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Max is right. There is only one oddball light (other than the headlights) which taps from between the batteries and that is the high beam indicator. The dashlight uses a resister on the side of the glovebox IIRC.
BJ 24v bad electrical design? (1 Viewer)
- Thread starter eleblanc
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I dunno. I recall in the DTLC days some fella in the prairies sending me an factory addendum light diagram for Cdn spec trucks. showing the 12V center tap system for the headlights. When I pulled apart my 1984 BJ42 to trace all the wires, it was close, but not a match for the diagram. I don't recall the differences, but know I recorded it somewhere.
Moral is, don't assume the wiring diagram is perfect.
Ya'll are making sure I get into the wiring on the 1981 BJ42 when it comes out from under cover this spring! I don't recall using any 12V bulbs in the dash, or seeing any. But that was a few years ago now.
Rob put a voltmeter on his light when back at the shop. Even though the housing says 12V, it was showing 23V or so if I am recalling correct. He'll confirm.
Moral is, don't assume the wiring diagram is perfect.
Ya'll are making sure I get into the wiring on the 1981 BJ42 when it comes out from under cover this spring! I don't recall using any 12V bulbs in the dash, or seeing any. But that was a few years ago now.
Rob put a voltmeter on his light when back at the shop. Even though the housing says 12V, it was showing 23V or so if I am recalling correct. He'll confirm.
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lowenbrau
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No load ?(i.e without the bulb) It won't drop any volts across the resistor. It would be normal to see nearly 24 volts then.
lowenbrau
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21.3 volts with the bulb lit up. My truck should be CDN spec; I have the original warranty receipt from the Frontier Toyota dealership in Winnipeg. My original owner's manual doesn't list the bulb at all.
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The B phase?
I looked again and it appears to be the B terminal, I misread the diagram.
I just spent the last several minutes studying the wiring diagram in my 1980 FSM and it shows the LH headlight getting its power from the fusible link that taps off the RH (ground side) battery and the RH headlight getting its power from the B terminal of the alternator (which is connected to the LH (high side) battery positive 24V terminal) but the RH headlight is operating on 12V because its ground terminal is connected to the the same fusible link as the LH headlight power side. In other words, the LH headlight is drawing its power from the RH battery and the RH headlight is drawing its power from the LH battery.
It is all rather confusing and makes one wonder if it would not have been easier to use 24V headlights, especially as any other bulbs I have ever had to replace have all been 24V.
I once had the wires break loose (corrosion) from the positive terminal of the high side battery (LH) while the engine was running and the only light in the whole vehicle that would operate was the LH headlight.
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That is really odd, i have 12V coming to this light.
We need to found out the electrical engineer of the time!
Wayne, here's a blast from the past: https://forum.ih8mud.com/diesel-tech-24-volts-systems/68379-78-bj-40-headlight-diagram.html
eleblanc, I'll be checking my 1981 BJ42 when it comes out of hibernation. Does not help you right now though.
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It sure is a mystery! I wonder if in 83 they made changes from the 81 model. For example, your dash looks different than mine.
Personally, I might just switch everything over to 24 volts in the future, especially if I ever have troubles with my headlight relays.
Greg, I didn't even know about Mud in '06 so I wasn't aware of that thread. Good description of a basically weird setup
My rig has 24v headlights. I guess I dodged that bullet by going JDM. I wonder if anyone has had resistors go bad and that my be the reason that you can run 24v dash bulbs now...
My '79 BJ40 always used 24v bulbs in the cluster right from new - they are so dim I replaced them with 12V which were wonderful for a few minutes before they fried. This was many years ago when the vehicle was nearly new.
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That could very well be the case with my truck. I'm just happy I have light that works in there now!
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No was just out of curiosity if you had 12 or 24v there
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The more you guys dig, the more weird stuff you're going to come up with. I'd suggest that you just stop digging... These vehicles have been on the road a long time, and have been generally very reliable given that the owner actually does some maintenance on them.
There is a resistor, as Bruce has stated, that is located in behind the dash near the ashtray. Again, as Bruce has stated, the voltage across a resistor that has no load on it is going to be very close to the system voltage. If you overload this resistor with even another small bulb or two, it's going to get a lot hotter than it already gets and shorten its life substantially.
Really, just replace the bulb with a matching unit and stop worrying. There are way more important things in life than generating a whole thread about a teeny little light bulb.
~john
There is a resistor, as Bruce has stated, that is located in behind the dash near the ashtray. Again, as Bruce has stated, the voltage across a resistor that has no load on it is going to be very close to the system voltage. If you overload this resistor with even another small bulb or two, it's going to get a lot hotter than it already gets and shorten its life substantially.
Really, just replace the bulb with a matching unit and stop worrying. There are way more important things in life than generating a whole thread about a teeny little light bulb.
~john
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Sometimes, it's the little mysteries that give a man purpose. Those of us with wives know that all too well.
Would you really rather read another turbo install thread?
Would you really rather read another turbo install thread?
