Ok here is what started this mess. I added a set of Fog Lights to my 1991 F-150 XLT Lariat 4x4. I ran all of my wiring and everything and had mounted switch into dash so it looked factory. I went to searching for a "HOT" wire that was 12V with key on. There was a wire hanging down under dash near brake panel, so I put my light on it and bam, light came on and went off when key turned off. I hooked this wire to fog lights but when I turned them on, they never came on. After doiing some checking, I found out that this wire hanging down was to test codes. (I had no idea) Now when I start my truck, the rear anti-lock light comes on and the red brake light. As soon as it starts, they come on and stay on and with them on, now my cruise doesn't work either. Also I noticed that when I start the truck, the rear tail lights are on dim, more dim than parking lights because I turn on parking lights and they get a little brighter. My question is, since this all started, could I have messed up something in the ECM? I have tried the code thing, and tried everything I know to get these 2 lights to go off and nothing has worked. Any suggestions guys? I am at the end of my rope chasing this thing!

 

I get it you reverted all the wiring to the previous last working configuration, right?. If you didn't, start there. What do you refer to as the "code thing"? be clear about what you're stating so we can actually help you, if you meant retrieving codes, what was the result? did you get the same results when re-testing? that would point at a consistently working ECM, which is a good thing. Have you tried disconnecting the battery for some minutes? this will clear the memory codes and probably turn off the pesky lights.

 

Those things are unrelated to the engine ECM, but without knowing exactly what wire you tapped into, we can only speculate what you have done.

Have you tried checking all the fuses?

 

I went by this and had to unplug light from master cylinder, but the codes were tested twice and same result. The Anti-Lock light flashes 4 times. The code says that the ABS Valve is closed. But if that was the case, this would have happened before I hooked up lights. This didn't start until I screwed up and tried to use this test wire as a hot wire.

 

Yes I have checked the fuses. All are good. I unknowingly used the code test wire ads a hot wire for my fog lights which didn't work when they were turned on, yet it lit up my test light when the key was on so I thought it was ok to use.

 

I would try unplugging the ABS computer and see if that resolves your tailight issue. If it does, I suspect your ABS computer may be damaged.

 

Is this a different computer from the ECM?

 

Yes, they are two different systems.