bj40 battery drain

[landcruiser78]

hello everyone, so far ive figured out that the drain is coming from the 12volt wire that connects right on the battery terminal, but because i cant find a wiring diagram i cant figure out where exactly the 12v wire goes, anyone know what the wire powers or have a wiring diagram they could share? its a 1978 bj40 with a B engine. it will drain both batteries in about a week from sitting.
Any help would be appreciated!

jonathan

 

[joekatana]

Does it have a 12v radio hooked up to 1 batterie?

This has happened to me in the past that badly installed accesories hooked up to only 1 battery vs using a 24/12 converter killed the battery life.

Bad grounds are another thing to check

Joe

 

[lostmarbles]

Here's a diagram for a 1979 Jonathan (but I'm not sure it'll upload to a size that can be read easily):

 

[Greg_B]

Is this 12V coming off the left side battery negative post?

If so, this is the evil center tap that Toyota used in Canada back in the day to run two 12V headlights on a 24V truck.

That 12V tap goes to a 12V dimmer switch under the drivers (LHS) dash. It's been a few years since I've poked my head under the dash of my BJ42 so I don't recall the exact location. That 12V dimmer switch also has a 24V lead coming into it from the main harness (positive post of the same battery). Inside the switch the evil center tap does its thing.

This link will have diagrams and a more complete wiring explanation: https://forum.ih8mud.com/threads/78-bj-40-headlight-diagram.68379/

When this evil center tap system is working correctly, the draw is balanced and there is no drain. Because of this evil center tap, you must make sure both headlights are working and when one burns out...replace it right away.

If you have another 12V tap (say...to the memory preset on your radio) or a PO has tapped into the 12V wire for something else...that might be your issue.

Do you have a 24-12V converter that would be drawing it down when you don't run it for a while? All converters will have some parasitic draw. On my 24V trucks I either disconnect the converter or hook up a trickle charger if I am not going to be running the truck for a while.

hth's
gb

 

[landcruiser78]

when i put the aftermarket radio in i installed a 24-12v converter that is also relayed to shut off when the ignition if off. greg that is the wire that is drawing, but can that dimmer module cause a drain even when light switch and ignition are both off?

 

[Greg_B]

when i put the aftermarket radio in i installed a 24-12v converter that is also relayed to shut off when the ignition if off. greg that is the wire that is drawing, but can that dimmer module cause a drain even when light switch and ignition are both off?

If the system is working as it is supposed to...no...there should be no draw.

Time to trace the 12V wire back, see if it's been hacked into somewhere by a PO, or if the relay is doing all it should.

To see if voltages are what they should be to balance each other you could unplug the harness into each headlight and check the voltage at each of the three pins on each light with:

Headlight switch off
Headlight switch on and on low beam
Headlight switch on and on high beam

This post has what a stock system should show at each pin: https://forum.ih8mud.com/threads/78-bj-40-headlight-diagram.68379/#post-786466

Some folks have switched it all to 24V and done away with the center tap system when issues have arisen with the dimmer switch.

hth's
gb

 

[landcruiser78]

i unplugged the dimmer module and its still saying i have a draw somewhere on that 12v lead. where else does this 12v wire lead to/power?

 

[Greg_B]

When I pulled the harness partially apart on a clean 1984 BJ42 years ago to figure out the headlight problem on my 1981 BJ42 I thought it simply went straight to the dimmer switch, but I did not have it completely apart. I took it far enough apart to figure out the system and then my 1981 far enough apart to find a PO hack, repaired that back to stock and its been all good since.

I would take the time to check each headlght pin to make sure everything is equal draw. Might mean pulling the dimmer switch apart to inspect as well, if a unequal draw shows up.

If the draws are all equal in the headlight system then perhaps start pulling a fuse at a time and narrow down the circuit (probably still come up headlight circuit anyway...but worth a try).

I can't see Toyota putting anything else on that wire as that would create an unequal draw.

You might have to follow the wire...

hth's
gb

 

[landcruiser78]

yeah ive already pulled fuses... shoot.

 

[landcruiser78]

so i put a voltmeter to the head lights...
R L
HI- 12.30v 11.75v
LOW- 12.27v 11.75v

is this saying i have a bad dimmer module?