Hey,

I was thinking about adding factory remote keyless entry to my 94 Blazer as a fun little project. Aftermarket probably makes more practical sense? Yeah...but this would be a fun project and I could have stock fobs! I already have power door locks and based on the wiring diagram it doesn't look like there's much of a difference to the circuit. I can handle the few splices needed. Based on everything I read, the factory keyless receiver would normally go in the center console between the front seats, but I don't have a center console. I have the 60/40 split bench seats. Looks like ordering keyless entry from the factory required bucket seats and a center console based on this document (page 21). I'm sure I can find a place to put the receiver around the dash instead.

I've attached the remote keyless entry wiring diagram from the factory service manual to this post. There's one thing that has me questioning my sanity. The receiver is able to unlock the driver's door separately from the other 3 doors so the first press of the fob only unlocks the driver's door, and then the second press unlocks the other 3 doors. So the driver's door is special and doesn't use the original door unlock relay anymore. But what about the interior unlock switches? Based on how I'm interpreting the circuit diagram, the interior unlock switches would only be able to unlock the other 3 doors after installing the factory keyless entry module.

Am I missing something? Is that normal on these? On first gens with factory keyless entry, do the interior unlock switches fail to unlock the driver's door? Or is there more to the circuit internal to the receiver that detects that one of the interior unlock switches was pressed and unlocks the driver's door at the same time? Am I misinterpreting the circuit diagram? From what I can tell, the driver's door unlock will be controlled solely by pin B on the remote keyless entry module...right? So how would the interior unlock switches be able to tell it to unlock? The rest of that section in the service manual doesn't elaborate on it at all. It just says that pressing either interior switch "unlocks the doors", so it's not much help.

Thanks for any info!


Circuit diagram from factory service manual for keyless entry on 4 door models from 1994

 

5 cents worth.

I own a 94 and the circuit is really primitive. The internal switches located in the front driver and passenger door simply actuate "all 4 door locks".

I guess it would be no different with the FOB. First press activates drivers door. Second press activates all 4 doors?

 

Thanks. Yeah, I saw the circuit in the factory manual for the 94 without keyless entry (like mine) and it's really similar to what I posted above, except all 4 door unlocks are hooked up to the door unlock relay connected to the interior switches. Very simple.

I'm still confused though, because the diagram above (with keyless entry) shows that the driver's door isn't directly connected to the interior switches. The only possible explanation I can think of is the receiver module takes care of unlocking the driver's door when it notices that either interior switch is pressed. But the diagram doesn't say that anywhere.

 

Fully agree on that one. Would need to detect the presence of a signal at "G" and then open via the KEM (keyless entry module).

One more of the mysteries of electronic boxes.

 

Thanks for confirming that I'm not crazy :-) I got the keyless entry module and wired it up on my test bench. Sure enough, with everything powered up, if you put 12V on pin G, a relay inside the module clicks, and pin B suddenly has 12V on it too. So the module is definitely forwarding the unlock signal from the interior switches to the driver's door. My sanity is restored.

Now I'm trying to figure out why when I put it in programming mode by grounding pin C, the relays click as expected, but then every couple of seconds the relays click again, almost like the module thinks it's re-entering programming mode again. And it doesn't pay attention when I press buttons on either of the remotes during programming mode either. Hmmm.

 

It's really too bad that there are no wiring diagrams and block diagrams of the various boxes in the 1st gen. The trucks are already very advanced and use a lot of electronic stuff which is not documented. We got all the diagrams to and from the boxes but sometimes need to figure out the inner workings. Reverse-engineering

Maybe to properly enter the programming mode it needs some kind of programming signal once it has entered that state? Nothing in the description thou. Maybe just ground the pin C once, remove it and then try programming? Possible that it just needs a short signal, then programming, then adding a short ground signal to C again to store?

 

I figured it out. Using the diagram above as well as other info from the factory manual, I was able to make an in-line adapter wiring harness that grabs all the necessary signals from C293 and C206A to pass them onto the keyless entry module (also isolates the driver's door from the other 3 doors so the module can control it separately). They use Metri-Pack 280 connectors which you can buy on Mouser. Both of the connectors are accessible under the dash on the driver's side, although C293 was really buried up there and hard to get to. I didn't have to cut or modify any of the factory wiring, which is great. I just inserted my adapter harness inline at those two connectors.

Putting the module into my Blazer resulted in the same issue I saw on my test bench -- it behaved erratically while in programming mode and didn't respond to key fob presses. I simply resoldered all of the solder joints on both circuit boards inside the module, and now everything works as it should. Soldering is kinda tricky because of the conformal coating on the PCBs, but you can still do it. I added a little bit of extra solder to each solder joint so that some new flux would help everything flow.

And just to confirm, the programming process is simple. You ground the purple wire that goes to the data link connector, and then the door locks and rear window release will all cycle. Then you press the lock button on your fob, which causes the locks to cycle again as a confirmation. If you want to program two fobs, you then press the lock button on the second fob and the locks will cycle as a confirmation again. Then you unground the purple wire. That's all there is to it...anyway, I'm really happy! It was a lot of work but I was able to add factory keyless entry to my Blazer!

 

Awesome job! Glad to hear you got it.

 

Hey, thanks! I'm working on a YouTube video series about it so other people can see the process. It's kinda boring watching me rambling on about the circuit, but maybe it will be useful as a reference tool for someone else who wants to try this.

 

Hi All, does anybody have a drivers side power door lock switch for a 1987 S10 Blazer. I guess 1987 is a rare year. If you do please try to contact me at cliff70chevy@gmail.com thank you. Also I am still trying to find out if the Plug for the factory PDL module should be under the center console if the Blazer did not come with that option.