Omak90truck

Help! I am at wits end with my 1990 4wd pickup (DLX reg cab 3VZE manual transmission manual wheel hubs). The 4wd indicator lamp won’t come on. 4wd works (I put the truck in jack stands to test). The indicator switch on the transmission is working (continuity in 4wd, none in 2wd). There is power to the indicator switch (voltmeter shows 12 volts). The bulbs is good (tested in another slot on the combination meter and checked continuity). The circuit on the combination meter tests good (continuity between D4 and D12). The truck has manual locking hubs, so no issues with ADD and vacuum lines (fortunately). The only thing left to check is for a break in the wiring. But, I don’t have a clue how to trace the wires. The wire connecting to the combination meter for the 4wd indicator is green with a yellow stripe and silver dots. The wires coming off the indicator switch on the transmission are green with a white stripe and red dots, and white with a black stripe and red dots. Clearly, the wire doesn’t go directly from the indicator switch to the combination meter. I’ve look through the wiring diagrams in the Chton manual, the Haynes manual and the 93 field service guide. They don’t tell me what I need. They show the combination meter and the indicator lamp D4 to D12. I can’t find where it shows the wiring from the plug to the indicator switch. I can’t physically trace these wires because the go along the top of the transmission, and they’re wrapped in the harness. I would have to pull the entire truck apart to physically see where the wires go.

What am I missing. Does the indicator switch connect directly to the combination meter? If not, what does it connect through? With ADD there would be a second switch on the drivers side of the transmission, but my truck doesn’t have that one that I can find. The wires from the indicator seem to get bundled with the oxygen sensor wires then disappear along the top of the transmission. I found some green with white stripe and red dots wires spliced together in the wiring bundle that comes from under the engine on the passenger side of the engine compartment, but one wire gets spliced together with three others, all the same colors. That makes me sense to me if it’s the 4wd indicator.

How can this be so hard to figure out? This should be a five minute fix, but my truck interior’s been torn open for two days now while I scratch my head at the very limited documentation. Does anyone have any suggestions?

mechkw

If I'm not mistaken--on my 86 the 4wd switch on the t-case is single wire indicating that it is a grounding circuit where-as when you shift to 4wd it grounds the circuit turning the bulb on. I don't know if the 90 is wired differently

Omak90truck

On my 1990 pickup, the indicator switch located on top of the transfer case has two wires. One is always hot at 12 volts. When 4wd is engaged, the indicator switch closes, completing the circuit. I have power at the switch, but I don't have power at the instrument panel, so there has to be a break in between those two points? Unfortunately, the wire from the switch is not the same color as the power feed into the instrument cluster, so I need to trace the rest of the circuit back to the panel.

Innocent Fool

My 90 V6 4x4 had a similar problem.
There is a 2 wire connector on the front diff that has 2 wires. Basically there is a switch that will connect the wires together to complete the bulb circuit.
Check the connector/wires etc to make sure they're ok.

As I remember you should be able to short the wires in the connector together with a paper clip and the light should turn on if the tcase is in 4x4.
It's been a while since I did it but something to check

Hairyberry

If it came with the add system then it has a switch in the front end. I had a problem with my light not working because all of the wires going to the switch in the front end were MIA until I found them in the engine harness by the oil filter and rather than hooking them 2 back to the switch I just spliced them together so I was taking the switch out of the equation because the add system is bypassed anyway. I would check the switch in the front end and the wiring there

millball

If the truck is/was equipped with ADD, the transfer case switch is not directly involved in lighting the 4WD light.
The 4WD light is lit when the ADD shift collar position switch at the front differential is closed.

Omak90truck

This is really interesting. I know I have an unused wiring connector down by the oil filter that the wiring diagrams seemed to indicate was for ADD. My pickup definitely never had ADD installed, so that connector was hanging unused. I can try tying the two wires together, but wouldn’t that turn the 4WD light on all the time? It’s important to note that the 4WD light WAS working, then it stopped about 6 months ago when the truck sat for a couple of months. That’s why I suspect there’s a broken wire somewhere.

2ToyGuy

It's a fairly easy wire to trace, and I noticed it had a problem with the connector that allows it to enter the wire harness for the transmission. I am talking about an 87 manual transmission 5 speed 4Runner, here. The switch that's for 4WD is on the driver's side of the trans, and the wire goes up and over the trans, to a connector from the main wiring harness that comes down from above. A round green, single wire connector. The female pin in the connector, that the wire comes over from the switch goes into, constantly came loose from the connector, and pulled loose, eliminating the 4WD light.
I spread the pin's ears a little, and most importantly, I added about 4 inches of wire to the whole affair, on the part that comes over from the switch. These two actions, simple and easy, solved the entire problem. The wire from the switch was JUST too short, causing the wire to pull out of the plug when the whole system flexed, even on light offroad. I had to go over that kind of road to get in and out of my property. About 1/2 mile worth. So I could fix the problem in my driveway, go to the store, and pop! No more 4WD light. Adding the extra wire allowed it to flex enough that it no longer pulled loose.
In addition, I put a dab of silicone dielectric grease in the plug, to keep the dirt, water, and so forth, out of the plug.

Good luck to you!
Pat☺

Boredmuse

Good info, thanks

Softailrider00

Did you ever find your problem OP?

Omak90truck

I have not solved that particular problem. It’s mostly because I’m not very good with electrical, but also because the wiring junction that was mentioned is up above the transmission, so I haven’t figured out a good way to get a look up there. There are times when I think Toyota went out of its way to make repairs more difficult than they needed to be. As great as these trucks are, and how long they last, imagine what they would be like if they were designed to be easily repaired as well. One can always dream.