View Full Version : SES Light - older CARBED car

01-19-2008, 05:57 PM
Hey folks I'm working on my 84 Century project car today. It originally had a carburetor with an ECM that controlled timing only (I think?) and it has a Service Engine Soon light in the dash. I want to connect this to my current ECM for the TBI conversion but something screwy is going on with the Check Engine light.
Even with NO ECM connected, the SES light is illuminated on the dash. According to the diagram for tihs car, there is some kind of lamp driver box in this car. I need to remove and bypass this lamp driver so that I have a straight wired circuit between the SES light bulb and the ECM. Can anyone point me in the correct direction to finding this item?

01-22-2008, 03:46 AM
84 Century...carburetor with an ECM that controlled timing only (I think?).......Even with NO ECM connected, the SES light is illuminated on the dash.

Chiltons is not much help....not knowing which motor is not much help either....but, say it had a Vin E (3.0: 1984):

1. SES circuit is 12 Volt powered on one side, and other side of SES goes to:

a. Data Link Connector and a
b. Light Driver Module (LDM), which has a ground side.

So, one of these two (a & b) or both must be provide a ground to light up SES light. They show a Yellow Wire from SES light going to this LDM along with a PNK/BLK Wire attaching to this LDM.

ECMs in that era were more complex...even my 1981 Chevy V8 had a full set of sensors in it.

Now....I just snipped the below information...I did not read it....but you might give it a try:

All carbureted computer controlled cars use a Lamp Driver module (http://www.howellefi.com/shop/skin1/pages/US/instructions_monte_carlo.pdf) between the computer and the “service engine soon” or “Check Engine” light. TBI or TPI computer vehicles do not use a lamp driver, instead, are wired directly from computer to SES light. (through the IP harness connector). It will be necessary for you to wire around this lamp driver to make your SES light work correctly with TPI.

The Lamp Driver module is taped to the IP harness near the computer harness connector (white plastic 15 pin on my harness) It has four wires going to it. Clip the yellow one, and the white with green stripe wires and join them together. Solder and tape this splice. Now your SES engine light should work correctly with TPI.

01-22-2008, 03:51 AM
That is exactly what I needed to know, thanks for looking that up!

While I figure out what to do about the damaged engine, I'll look for this module.