LJ78 Electrical?

[Gene45]

LJ78 Electrical (1990) ?

I apparently have slow leak in my electrical system that drains the battery over two weeks to the point where it won't start the engine. The battery has been checked and pronounced "GOOD".

I started checking at the fuse box by pulling the fuses with the engine, and everything else, OFF except the warning light that the door is open. Everything shows ZERO voltage except something called ECD which measured 12 volts.

I tried starting the engine with the fuse pulled and it runs, but what IS the ECD, and why do I need it? Emission Control Device? Exhaust analyzer?

Who knows?

 

[Rummat81]

ECD stands for ELECTRONIC CONTROLED DIESEL. ie. it could be the Fuse for the ECU.

 

[Radd Cruisers]

The only real test for parasitic draw is to use a low amps probe or an ammeter on the battery to measure the draw. Any draw more than about 0.05 A will draw your batteries down - less is better, but your clock will use something like 0.004 A.

You cannot do this test with ANY lights on or doors open. Even the idiot light in the dash is too much to give you an accurate value.

Common draws come from aftermarket stereos (certain removable faceplate stereos will draw 0.1 - 0.2 Amps while the face plate is in place and the stereo has not been wired correctly), diodes in alternators, aftermarket wiring, alarm systems, bad batteries and the like.

I just dug up a link for you: Battery Drain Parasitic Draw Testing

~John

 

[Gene45]

My first test was with the battery disconnected, I measured the resistance of the truck, the digital meter started at a small negative number and counted down to zero and slowly counted up for as long as I continued. My guess is that there is a capacitor somewhere that had to discharge and then recharge.

I pulled each fuse and checked each circuit for voltage across the fuse terminals. The dome light is impossible because the door warning light is always on, and I could not figure how to do this with the door closed.

The only circuit that showed voltage was the ECD.

According to the parts list in the sticky, there is a relay in this circuit. My guess is that the relay is there to energize the computer when the switch is turned on, and that the relay is stuck closed, so the computer is on all the time.

Now my challenge is to find the relay.

 

[SimonInAustralia]

I pulled each fuse and checked each circuit for voltage across the fuse terminals. The dome light is impossible because the door warning light is always on, and I could not figure how to do this with the door closed.

Can't you just use some tape across the door courtesy switch to hold it in/closed? Would be the same to the truck electrics as actually closing the door.

Not sure if measuring voltage is what you should be doing.

Did you read the link that John posted?

You should be checking amps being drawn from the battery, and then pulling each fuse until anything drawing too many amps is located, then troubleshoot that circuit.

 

[Gene45]

Can't you just use some tape across the door courtesy switch to hold it in/closed? Would be the same to the truck electrics as actually closing the door.

Not sure if measuring voltage is what you should be doing.

Did you read the link that John posted?

You should be checking amps being drawn from the battery, and then pulling each fuse until anything drawing too many amps is located, then troubleshoot that circuit.

I wanted to hold in the courtesy switch, except it seems to be hidden inside the door. Other vehicles I have worked on had a button on the front door post to control the light, This one does not. The switch is apparently inside the door and controlled by the arm that reaches into the door.

Re: voltage versus current. I agree that measuring current will tell me if any circuit is drawing a lot, but voltage will only tell me if there is a closed circuit from the battery thru that fuse (and its associated parts) to ground.

Whether I do it from the battery or the fuse box should achieve the same thing, identify the circuit that is leaking. I used voltage because my amp meter is blown.

And yes I did read the link. Now I need to FIND the actual parts on the vehicle.