Hi guys. I have a 1990 4x4 regular cab pickup with the 3VZE engine. When I bought it, the truck was in bad shape with a blown head gasket among other things, but it was rust free and I needed a serious offroad truck, so I bought a rebuilt engine and paid the shop to install it as well. The engine was ok, but the install was utter garbage. They used the cheapest parts and did as little as possible when slamming it in. Which brings me to my problem. It looks like they ripped the wiring harness back when they swapped the engines. Cable management clips are all broken, and wires were hanging all over the place. I’ve restored some order to most of the wiring, but there’s one issue I can’t make out.

There is a wire that comes from the harness running across the front of the engine that runs down the side behind the alternator, then splits in two directions. One path leads to a copper domed component at the bottom of the crankcase in front of the oil filter. The other wire is dangling. I need to know what to do with them. I’ve looked through the parts catalog, and I can find the wire listed, but it has a generic name (wiring harness) with no information about what it connects to. I’ve looked in the FSM, a Haynes guide and on the internet, but I can’t identify what these wires are.

I had to start fixing the problems with the engine install (wrong ignition coil wire was melting the coil housing, the distributor cap and rotor were worn out, the thermostat failed, a coolant hose was leaking, and so on) so I was able to take pictures and look around. One picture shows the wire coming from the harness, one shows the connector at the end of the loose wire and the last shows the component the other wire runs to. Any help identifying the wires and how they should be run would be greatly appreciated. Thanks!

 

The one next to the oil filter is the oil pressure sending unit. It'll be a few more days before I get home and can look at my 92 for the other.

 

Thanks. That's helpful to know. I can see the two wires in the parts schematic from Toyota, but it doesn't show what they connect to and the names are super generic (wire or connector, wiring harness).

The wires I'm trying to identify

 

Can you get the wire colors? G-Y and P-G could be the ADD indicator.

A photograph of a plain connector, even a good photo of one not covered in grease and mud, isn't really that helpful. The EWD will give wire colors, but the connectors are usually pretty similar.

 

I peeled back the tape and checked the wire colors. There is one yellow with green stripe wire going down to the oil pressure send unit. The second wire was wrapped in tape, then it and the yellow with green stripe wire were wrapped together. There are actually two wires going to the connector. One is plain green, the second is green with a yellow stripe.

 

G-Y does appear other places (right turn signal, Day-time running light, COR, cruise control ....), but I don't see it anywhere else going to a 2-conductor connector. P-G is purple with green stripe. Wire color can be tricky; at a minimum, you have to spit on your thumb (ick!) and rub the dust off the wire to read the color(s).

Have you tried taking a look at the ADD, to see if you're missing a wire?

 

I went back down and reconfirmed the wire colors. The single wire is definitely yellow with a green stripe. The other two wires are green and white and green and yellow. I’ve attached pictures of the wires.

Also, I was cleaning off the plug and part of it dropped off. I think it’s a situation where there’s a connector and a hood over top of it holding it in place. I’ve included a pic of that.

I went looking for the ADD. I’m fairly certain I’m looking at the same place, but I don’t see the component at all. I’ve included a picture from the same perspective.

 

My EWD shows G-W all over the place (DRL, EGR Gas Temp Sensor, Horn, Parking Brake, Stop Light), but not with G-Y. So I've reached the end of what I can do.

I don't see your picture of the ADD. My photo is looking at the front differential, from the front (the tire is the right front).

 

You didn't say--manual transmission? My 1991 diagram shows G-Y and P-G for auto but G-Y and G-W for manual:

 

It is a manual transmission. Please correct me if I’m wrong, but doesn’t ADD stand for Automatic Disconnecting Differential. I don’t have that on this truck. It has manual locking hubs on the front wheels instead.

 

What isn't working on the truck? I have plugs from the factory OEM wiring harness not connected for systems I don't have. Swing the wire about as it can only connect to something within reach. If nothing is missing a plug, it may be a none use wire. Just saying. It it ain't broke It doesn't need fixing.

 

Yeah, I think you’re right. It could very well be unused wiring for the ADD. It’s not very long, and I haven’t found anything else around the oil pressure sending unit that it could connect to. I started looking because the engine was running a bit rough, but replacing the spark plugs, plug wires and ignition coil with OEM parts seems to have fixed that problem. I’ll tape it off for now until I find something that’s not working. Thanks for your help!

 

The only thing I have are two water temp sensors for the cold start injector and the ECU in the upper front of the block near the throttle body.

Do you have AC with a compressor located below the throttle body? Here's a pic of the AC compressor clutch connector that looks like the female plug to your male plug. If so, maybe the female connector/wire dropped behind the AC compressor.

If not then it could be just an unused AC plug. I have no idea what the 3 or 4 unused plugs on my 86 are for, but haven't had a problem in 36 years of driving it. Maybe one day you stumble onto what it's for.

Good luck.