Was emissions computer maybe something else electrical? (1 Viewer)

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isaacfinnegan

isaacfinnegan

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May 6, 2013
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So I just ran a bypass to the ignition for the fuel cut solenoid. It wasn't ever opening and was killing the idle. Testing it, it was not getting any current on the wires going to the plug on the carb.
After doing this, I noticed some weird behavior, and I'm wondering if I have a general electrical problem instead of the emissions computer being bad (my current assessment).

Right now, my running lights and dash gauge lights don't come on. And if I turn on the lights (one click on the wheel stick switch) then the dome light goes off.

Tail/running lights: not working
Dome light: works until tail/running lights are turned on.
Dash gauges light: not working

Any ideas? I'm planning on doing some electrical testing somehow next.
 
Current assessment - Is that a pun? :rofl::rofl:

The Emissions Computer works thru neg ground. So you're saying to wired the ICS directly to 12v+ and neg and you got the 'click-click'?

There is also a fuse for the ICS.

Also @OSS has several threads on the connector behind the cluster that binds all the neg ground wires together - It often is a problem for strange electrical issues. Maybe he has a pic handy. I can't find it at the moment.
 
Ok. will check that. Also fan/AC blower is not working. Seems like all internal is off. I didn't notice, as the radio has a dedicated power i put in to deal with electrical noise.
 
Electrical mayhem in the cab (in my experience) often is caused by a burnt grounding junction. There's a multi pin/multi wire connector behind the instrument panel that acts as a (inadequate) grounding bus for several circuits. Lots of stuff (ground wires) join up there to be routed to a larger wire that terminates to body ground up under on the driver's A pillar. It's not uncommon for the headlights or fan to eventually burn up that ground connection, creating electrical resistance.
Once the good path to ground is lost, accessories take the next easiest path of less resistance—often through another ground wire back through another accessory. It's called a floating ground and causes all kinds of weird behavior with the electric stuff. Like push a switch and something unrelated sort of turns on too.

Remove the gauge face plate and look for a plastic covered multi-wire connector tucked in behind the wiring harness. It will have a bunch of black wires and blue wires going into it.
Look for any evidence of melting or burning.
 
Thanks for the pointer. I've pulled the gauge panel, but can't seem to find the connector you are referring to. A pic is below. While I can't smell anything burnt back there the behavior seems like it fits what you describe @OSS . The dome light doesn't work via the swithc, but when the door is open, the dome light comes on (dimly, which is weird as it's LED). But if I turn on the parking lights (one click on the left hand steering stick) the dome light goes off, and there's a delay to it coming back on when I turn off the parking lights.
So, no AC blower, no parking lights, no brake lights, no gauge lights, and Isuspect the emissions computer also has no power, as I had to bypass it to have the fuel cut solenoid wortk. But, headlights work, turn signals and hazzards work. Not sure what else to check for. I pulled the tail light relay which was not clicking. When the tail lights are off, there's only 6v coming from one of the connectors, and when I turn the parking lights on, then that drops to 0.

Not sure why image isn't working: https://photos.app.goo.gl/MRPvfRZnwJc2kfBV9
UntkxXY2M95ZFJtV9
 
Last edited:
@OSS I found the grounding bus and it's totally fine. When I pull the connector out, I only get a ground through one of the terminals and none of the others. I have been doing continuity tests and I feel like I have a short somewhere in the parking light system. When I test the brake bulb receptacle I get only 7-20 ohms resistance across either of the positive leads (parking or brake) and the grounding sheath. Is that right? Even with the car off, switches off. Even with the parking relay pulled.

The thing that's throwing me, is I also get continuity across the turn signal bulb leads as well, but the turn signal is working fine. Backup lights get no continuity when off.
The other thing that is kind of odd, is how the dome light only works with the door switch but when I turn on the parking light, it goes off. This makes me think there's a short or it's grounding out through the parking switch. This also still happens with the parking relay pullled.

Next I'll be fully disconnecting the trailer hookup in case the issue is there, although from visual inspection it seems like all that's fine, but not sure what to do next.
 
Trailer hookup can definitely be causing an issue. Also check the fusible links to make sure that you have not blown or broken the link that controls most of the interior lights.
 
So a couple corrections. Looks like I wasn't ever pulling the correct relay. It took a replacement to realize this. When the parking relay is pulled, then the dome light stays on even when the switch is turned on. So this leads me to believe there's a wiring issue somewhere in the parking lights. The trailer hookup is disconnected, but I may need to actually disconnect the wires where they are spliced in. Still not sure what I should be expecting for continuity across the brake/tail light leads.
 
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