91 Suburban Nightmare

[KazuyaIB]

First of all let me state that I am lost but maybe someone can help or at least guide me in the right direction...

My suburban started dieing on me last night. The low beams and interior lights go out as well as the ECM B fuse has no current going to the fuse...

I see no connection between the lights and the ECM B fuse...
The weird thing is if i let it sit over night it works the next morning great but as soon as i turn the low beams on within a couple of minutes it dies.... Wiring issue? Wonder if anyone has had this problem before. Any help would be amazing, thx

[packratcffc]

How old is the battery?

Do you have any way to "load test" it?

Is the truck charging at the corect voltage?

Check all the battery conections make sure there clean and tight.

Check you ground conections to. The one for the ecm is on the intake manifold next to the water neck. There also is one on the fire wall pasengers side.

[hatzie]

Originally Posted by KazuyaIB

First of all let me state that I am lost but maybe someone can help or at least guide me in the right direction...

My suburban started dieing on me last night. The low beams and interior lights go out as well as the ECM B fuse has no current going to the fuse...

I see no connection between the lights and the ECM B fuse...
The weird thing is if i let it sit over night it works the next morning great but as soon as i turn the low beams on within a couple of minutes it dies.... Wiring issue? Wonder if anyone has had this problem before. Any help would be amazing, thx

The dimmer switch and ECM B are fed from one of the fusible links on the starter.
See the attached schematics for details.

[RastaRobb]

Sounds like an alternator problem to me. The lights are running off the battery, but the battery is not getting recharged from the alternator. In the morning, your battery has had to time to recover, and can power the lights for a minute. The alt may be working just enough to keep the engine running, but soon that will die too.

[RastaRobb]

You can check it by starting the engine, and while it is running disconnect the battery cable. If it dies, you know the alternator is not working, as it should keep everything running.

[hatzie]

I assume you tested the ECM B position with a meter and it read 0 volts...

A bad alternator will discharge the battery to 8 or 9 volts. The ECM and fuel pump stop working at 8-9 volts but the interior lights would still be dimly lit. A bad battery or loose battery connections will do the same thing.

If the ECM B position has 0 or 1-2 volts it's a damaged wire. It heats up from the load of the headlights and the gap between the conductors gets large enough to turn off the truck. I have had a fusible link do this.

Ohm out the wire from the starter to the right hand terminal of the ECM B fuse socket on the fuse panel. Run the truck till it dies and ohm it out again. Both should show a dead short or close to 0 ohms. If the resistance rises after it's hot you found your open wire. Examine the wire at both sides of the bulkhead block and fuse panel to make sure it's not damaged or badly corroded there.

[motornut]

check if you have a trailer hitch
i had a short only when using the lights....killed the alt
found a bare bit touching under the hitch 1988 burb
I drove ok with no lights,but it slowly dimmed the lights out till it died

[KazuyaIB]

THX for all the help guys with possible issues and the problem was one of the main wires that goes from the harness to the alternator that supplies the current to the lights and that fuse. Only had two threads holding on which explains why once i turned the lights on the power would shut off.