Hows it going? I've searched around this board and found very little info regarding the 12V switched wire on the fuel pump relay for an '89 GTA NTM I don't have a multimeter. The colors for the fuel pump relay wires mentioned in other threads I read didn't match mine at all. I'm in the process of installing a 4-wire o2 sensor on my car and would like to know which of the following wires on my fuel pump relay are 12V switched: Orange (large diameter), Orange (smaller diameter), Green/White, Black/White, Tan/White. Any info is appreciated. Thanks, Phoenix

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It's the tan/white. But don't use it for the O2 power, it's not the right place to tap into. I'd go from ignition or another wire.

Nina, your wire is grey because you likely have a newer year harness. Yeah, good o' Cheby, they could not make up their mind even on wire colors.

Lou

Yeah another guy on this board installed a 4-wire o2 sensor as well and his 12V switched wire was grey as well; his is a '92 GTA btw. Thanks for the tip on the test light NINA I'll try that out tomorrow.

So I shouldn't tap into any of the MAF power, Fuel Pump or MAF burn-off relays? Installing it via ignition would mean running it through the firewall into the fuseblock correct? Thanks for the information Lou. If only GM knew that using the same wire colors would make our lives alot easier .

Phoenix

The FP and MAF are powered from the 20A inline fuse by the battery which is already maxed out.
If the O2 sensor heating element requires only an amp or two, it shouldn't be a big deal. Knowing O2 sensors, however, I am afraid it's a little more current than that.
You could tap into the brown wire that goes to the alternator, it powers the fan relays and the alternator excitation field so it has some spare "room".

Hope this helps.
Lou

I see. All of the information I researched regarding the installation of 3-wire and 4-wire o2 sensors, always suggested tapping off of the f/p or MAF switched 12V wire. Would tapping off of those relay wires burn out the sensor? I never thought of that but it makes sense and I think that it will kill the sensor. I'll tap into the brown alternator wire instead. Thanks for clearing that up Lou. Since we're on the subject, is it true that the 2 ground wires on 4-wire sensors have to be installed seperately? I appreciate the information.

Thanks,
Phoenix

As for the grounds, the 3-wire sensor is grounded through the exhaust so obviously it doesn't matter where the ground comes from.
Good ECMs run a separate ground from the ECM case to each sensor, though.

Lou

Makes sense . I'll be installing my o2 sensor tomorrow and let you know how it goes. Thanks again for the information Lou.

Phoenix

I removed my old 1-wire o2 sensor today and it looked like its never been changed before. It was completey covered in soot, as well as there were deposits on the inside of the fins on the tip of the sensor. My 4-wire sensor and pigtail are actually not long enough to reach the fuel or MAF relay wires but I'm not however thanks to BigBabyLou, I was recommended to tap off the brown alternator wire for "key-on only" operation. The sensor's wires are near that particular alternator wire btw. I'm going to use a wire tap made by 3M such as this one:

to tap into the wire. In my case all I would do is slip each wire side-by- side into the openings you see there and crimp that grooved metal piece down with pliers. As you do that, the metal piece digs (cuts) through the wire's plastic sleeve contacting the bare wire only in between each groove. This provides a connection beteween the 2 wires. Pretty cool little trinket if you ask me . I'll post my results.

Later,
Phoenix

Installation is done. I noticed the car now heats up in about 2-3 min. as well as run smoother. I used the 3M wire tap to tap the pigtail's 12V switched wire into the tan/white wire from my alternator. I then twisted both remaining grounds together and crimped on a ring terminal to slip into the ground bolt on the back of the driver's side head. Plugged in the o2 and ecm signal connectors and called it a day. Once again thanks very much for your input Lou it was a big help.

Later,
Phoenix