Harness short?

[Desert Patina]

Hello,

Well it looks like something went wrong in my harness swap, but I don't know for sure.

I just hooked up the battery to the ECU harness without the ECU to see what is getting power right now. I plug the negative lead into 60 (ground) and check if there is voltage at any of the other leads at the ECU.

Should circuits like Ignition Diagnostic, Self Test Output, Boost Control, EGO Ground, PIP and Ignition have power when the key is out?

The bigger problem I'm trying to fix is that when the ECU is plugged in the check engine light (this is an LA3) comes on whenever the battery is connected.

I'm not in over my head ... yet, but any help would be greatly appreciated.

[Desert Patina]

I think the fact that case ground shows voltage is proof I've got it hooked up wrong somewhere...

[Desert Patina]

Well, case ground lights up with voltage only when the engine harness is on the starter relay with the positive cable from the battery (only).

I did check all the leads without power for resistance, and none of them showed connectivity. (tested by plugging black into 60, and red into each lead). Well that isn't true, the AC switch showed power, but that is because it is connected to a diode. When I plugged red into 60 and black into AC, it showed no connectivity again.

[Desert Patina]

There appears to be connection between case ground and the previous mentioned items, but the least resistance to neutral input, which didn't show any voltage in the battery powered test...

[Desert Patina]

So, in further testing ... I've determined that the check engine light must be powered by a short in the ignition. Perhaps the switch is bad, perhaps the short is in the main harness itself.

The check engine light doesn't come on unless I've hooked up the starter relay connector on the main harness. I've disconnected the neutral input, and I need to retest the engine harness. I also figure there is probably a diode on the ignition circuit as well, and I should retest it with the red on the ground.

After that it is unplug everything and try to find where and how I plug something in when the short shows up.

[Kendal Coker]

ignition switch's are know to go bad and cause lots of problems. I have had them fall apart when I took the steering wheel cover off. They are only around $10 at the parts store.

[Desert Patina]

Now, this is impossible?

Here's the deal, imagine a starter relay where there is voltage at the lead you put the Red/Light blue wire (that comes from the ignition) on. That's impossible enough. When the ignition switch closes and provides voltage to that lead, that is what triggers the relay to begin with.

Now, imagine that this doesn't happen all the time. If the battery is connected to its very large lead, there is no voltage at that smaller lead. If the main harness is connected, there is no voltage at the little lead.

Only if the engine harness is connected on that large power lead does the voltage appear.

Well, you don't have to imagine, that is what is happening on my car right now.

What???

[MikeFleming]

Using a [high-impedance] DVM or a test light?

Make sure the BODY of the starter solenid is properly grounded to the chassis (sheet metal screws into the inner fender) or else the starter solenoid coil (what the power goes through) isn't a complete circuit.

Next - don't be afraid to toss parts into the trash bin and use new ones - such as starter solenoids.

[Desert Patina]

Analog Multi-Meter (set at voltage). The S lead is registering around 12-14V.

I'll check the grounding with the meter, but I know it is screwed in with sheet metal screws.

Also, just replaced the starter solenoid, and the issue persists.

[Desert Patina]

Okay, I think I'm coming full circle. I think what is happening is that there is insufficient grounding somewhere in the engine harness, such that ground is hot.

Even in straight forward circuits (actually all the power circuits), I'm getting a negative voltage, as if the power is running out of ground and into power. This reminds me of how I was getting voltage from the case ground earlier.

I think it is that reverse polarity through the starter relay that is causing the voltage at the S terminal.

[MikeFleming]

Do you have the correct EEC power feed wire lug on the battery positive post on the solenoid and not an EEC ground lug instead? or both?

[Desert Patina]

I'll have to double check the harness itself. I mispoke above, the voltage in the chassis shows up highest when the main harness is connected.

All the power ring terminals are connected to the same terminal on the starter relay, with the starter being the sole entry on the other side.

Now that I've solved most of the mysteries, its a matter of plugging in the main harness, and validating the connectors.

Also, I don't know if I can postpone anymore. Racing might now be a lost dream. But that is okay, I feel strangely invincible having broken through that deadline and remained alive.