dwreck333

Ok so i have searched everything i can think of on this forum and no one seems to have the same issue i am having. I have an 88 Toyota pickup 2wd 22r. My problem is i have no power to the rheostat the TAIL fuse is good along with all of the other fuses. I replaced the tail light relay also not the issue. I have power to the ac/heater lights i verified that first by the fact that it lights up and second via the green power wire i checked with a test light. Also there is no stereo and i went through and verified none of the loose stereo wires were grounding out. Tail lights also work as do the Battery and Oil lights etc when i turn the key on it is just the back lighting that doesn't work. None of the dash lights are burnt out either. Any ideas on what could possibly be my issue would be very appreciated. Thanks in advance.

scope103

The AC switch has a green light that illuminates when you activate the switch, and it has back-lighting. I assume that when you say you have power to the ac/heater lights you're talking about the back-light, not just the power indicator.

The rheostat is on the ground side, so if the back light of the AC light works, you should have voltage on the non-ground side of the rheostat when turned to max-dim (at max-bright, the rheostat is just a short to ground, so you shouldn't get voltage on the non-ground side).

The back-light to the AC switch, and the back-lights to the heater panel, are all on the same circuit as the panel lights. So you're getting power through the Taillight Relay and the Tail fuse.

This suggests a problem in the combination meter, or the wiring to the combination meter. My schematics show the panel light power on pins 1 and 2 of connector C8 (blue?) to the combination meter. You could check for power there.

dwreck333

I'm not sure what a combination meter is. If i remove the rheostat and run my test light to the power wire coming into it (red/black) i have no power to it. i also have an 88 4x4 22re and when i remove the rheostat i have power to the red/black wire on it so what i cant figure out is how my 2wd is not the same i know the red/black is power and the white is ground I've traced the rheostat wires back to the main harness and it reaches a point where its two wires break off into 1 i really don't want to cut the whole harness apart so i was hoping to find out where that red wire that comes in from the main harness and splits between the dash and the rheostat ends. the AC/heater is completely illuminated at night so i would consider that the back light, i'm not talking about just the AC "button" but it also turns green when turned on

scope103

What you call the "Instrument Panel" Toyota calls the Combination Meter. http://personal.utulsa.edu/~nathan-b.../6combinat.pdf

My schematics are for a '93, but they are generally the same. In the '93, the rheostat is between the panel lights and ground. The ground side is W-B, the lamp side is W-G. When the rheostat is "full bright", it's just a short to ground, so if you measured voltage to ground on the lamp side (with the rheostat still in circuit) you would get ground. At "full dim" you would be measuring the voltage drop across the rheostat, which I would expect to be in the neighborhood of 6v, less if you only have a few lamps (AC?) in-circuit.

If you remove the rheostat (no longer in-circuit), the W-B wire is to ground, the W-G is to 12v THROUGH some lamps. Since there is no current in the lamps there can be no voltage drop, so with the taillight relay closed you should get 12v.

So it depends on how you measure the voltage.

And just from the difference in wire color, the '88 might be completely different.

dwreck333

Ok well the only wire getting power on my combination meter is a green wire, it looks like the same one that runs to the AC, what i mean by that it it has the same markings as the green wire that has power at my AC/heater unit. As far as checking the voltage on the two wires that run to the rheostat that would be pointless since i can tell you it is 0v i say that because if it wont light my test light its not going to send volts through my multimeter. I can rule out the rheostat as the problem because i took the one out of my 4x4 and that didn't solve it. I believe the problem lies more in where the power source that the rheostat grounds out is coming from. Also on the same connector that has the hot green wire the pin next to that is the red/black wire from the rheostat that has no power.

scope103

I don't know which "test light" you have, but it's probably an ordinary 12v bulb. If you put it across the rheostat it is supposed to have 0v at "full bright," and still only about 6v or less at "full dim". 6v will probably do nothing at all to your "test light."

If you disconnect the rheostat and put your "test light" between the high side wiring and ground, you're trying to light a 12v bulb in series with some other tiny bulbs. Again, I wouldn't be surprised if you got nothing at all.

Which is one of the reasons a test light is a pretty much a waste of money now-a-days. Get a real multimeter. http://www.harborfreight.com/7-funct...ter-98025.html

If you have no voltage on the (disconnected) wire from the lamps to the rheostat, that tells you that you are getting no power through lamps. My schematics show the tail fuse to the combination meter wire is Green, so if you have 12v there then the next step is to look inside the combination meter.

Since your AC backlight works, (and that goes through the rheostat), your probably don't have a problem at the rheostat.

Electrical is just a matter of tracing from each end.

dwreck333

I already own a multimeter so i wont be needing that link but thanks anyways. I know that 12v runs through that wire on disconnect so it would light my test light if it had power. You might think test light wont work but i know it will i can put my test light on the rheostat on my 4x4 and i can brighten and dim the bulb just as it should i can also disconnect the rheostat and it will light the bulb of my test light so by this happening that would conclude that tye same thing would happen on the 2wd so why would my useless test light work on mt 4wd and not my 2wd? They are both 88, does my test light prefer 4wd? Lol