'88 4runner - How are the wiring harnesses broken down?
 

I'm not the best with wiring, but I can sort things out (sometimes.) I'm curious how exactly the wiring is broken down. Is it by system (ie: charging, ECU, fuel , etc...) or is it more or less by proximity (ie: this section of wiring harness deals with this stuff over here, and this section deals with that section over there, etc...) Specifically, I am wondering about the wiring that comes into the upper dash and supplies power/readings to the instrument cluster.

I'm running an SR5 cluster, with a oil gauge sending unit, and my oil pressure gauge is the only one not working. Up until recently, I had been using an aftermarket gauge to read pressure, but some loving thieves ripped it out. I have an old working aftermarket gauge I could piggyback onto the system (much like I had be doing), but I would rather rectify the situation properly.

I know one or two roadblocks stand in my way:
1st - On the wiring harness that plugs into the back of the gauge cluster, there are three plugs. On my truck, one is a large blue multi-pin connector. Some of the plastic on this blue plug has broken off, and the wire connector portions look a bit mangled.
2nd - Because I purchased this SR5 cluster secondhand, and because it has only EVER been installed with the above stated damaged blue plug, I have no idea of knowing if the OP gauge even works, or if it has been fried. If it works, I won't know until I get a good plug that has all connections intact. If it is fried, I'll have to source a new gauge/cluster.

So, long story short, I'm trying to find out how extensive the wiring harness is that plugs into the back of the cluster. Is it a short section that plugs elsewhere into a larger loom? Or is it hardwired into something that will require me to cut/strip/splice/solder something in?

I can't find a replacement "Instrument Cluster Wiring Harness" for this or other similar years/models (I did find a "Cluster Harness" for a '98 4runner on Ebay, but that's not gonna work for me...)

Does anyone have any ideas? I've never seen a wiring harness for these trucks outside of the truck...

Thanks,

Chris

The wiring harnesses on these 4runners (probably similar on most vehicles) are based on location. There is an engine wiring harness, but even certain wires for the engine runs through the body wiring harness. There is also a dash wiring harness that plugs into the engine and body wiring harness. Then there's the body wiring harness. The body wiring harness operates parts for the engine like the o2 sensor and the ignitor. There may be more to it without me going and digging through my 4runner. I would look at the source. Chase the wire coming from the oil psi sending unit, do a continuity test and see what wire at the end of the engine wiring harness gets continuity. Follow that all the way up to the gauge cluster wiring.