SES light reversed

[Drewster]

I've got a SES light on when it should be off and off when it should be on. No MAL codes on scan master. This is my friends 85 car who pulled the motor and did about 7 upgrades at once. Harness and 87 ECM upgrade included.
Is it possible the wires from the key switch to the SES light got put on a different contact to make it operate reverse ? He said he did say some wire fell off if the switch connector and he stuck it back in.
I had a bear of s time getting the car to start. But after I stopped looking at the SES light output it got easier. The SES light would be on with no ECM connected and go off when ECM was connected.
The car does now run and idle ok. Not perfect not to shabby either.
The new mods are
85-87 ECM
85-87 harness
Maf translater
Dual fan 85-87 upgrade with high lo
Heated O2 sensor
AIT sensor added.
60# Mototrons
TT chip

Any suggestion is appreciated

Andrew


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[GNVenom]

ECM presents a ground to light the bulb. One side of the SES lamp must be switched 12 volts. The other is directly to the ECM.

Can't imagine any other way it would work.

 

[Drewster]

definitely weird maybe I need to trace the wire in both directions from the bulb.

 

[Jerryl]

I am no GNVenom by any stretch of the imagination but sounds like there is power and ground with ECM disconnected.
Maybe the power drops out with with key on?

 

[RmvBfrFlght]

Was this originally a turbo car? If not there is a lamp driver for the SES that will cause this.

RemoveBeforeFlight

 

[Drewster]

RBF....what do you mean by a lamp driver? please explain more...
Its possible that is wasn't a 85 Ttpe limited rather just a limited. It has everything that a Ttype should although certain wires were missing at the ALDL like the Brown/white from the SES and the Orange wire from the ECM. Ill have to check the vin number and compare.
Yeah Jerry! I unplugged the ECM, turned the key only on, and the SES would light, plug the ECM back in, key only on, the SES would flash for 1 sec and go out... after about 4 hrs of troubleshooting, I chalked it up to an bulb issue.
John, yes it makes no sense when looking at the wire diagram.

 

[RmvBfrFlght]

On the CCC cars there is a module that is between the ECM and SES light. This module also provides a pull up for the ALDL serial data signal. It should be located above to the left of the glove box. I have a picture of the board, but not of the case. Appears to be about 1-1/2" x 2" in size.

You can remove the module and jumper the white and yellow wires together on the connector. Here is how it is wired in:

RemoveBeforeFlight

 

[Drewster]

Thanks for the info. Looks like that might be the issue. There is a yellow wire on the ALDL


Drewster on Tapatalk

 

[RmvBfrFlght]

If the yellow wire on the ALDL connector is in location D, this is the issue. To get the ALDL data stream working from the '87 ECM, can do this:

Move that terminal to location E in the ALDL connector.

Separate that yellow wire from the lamp driver module terminal and wire it to ECM pin A8.

Note that this feed goes through the C437 connector, location J ('87 Turbo is orange). This is the connector near the ECM under the dash.

RemoveBeforeFlight

 

[Drewster]

We got the scan master tapped off the orange wire at the ECM for now. I'll have to check out the pin D at the AlLDL. I believe that was it. I knew something was awry checking the pin out of the C437 and ALDL. I don't recall the pins and wires I left the marked up drawings at the owners house. Thanks for your help. I'll let ya know


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