1994 s-10 electrical help needed

In the book they share a common ground point.

Do any of the other interior lights that are attached to the same switch glow dimly? The dome lamp typically has 3 positions, off-auto-on. Do you have 3 positions in this car or just on-auto?

is the rearview mirror somehow attached to the dome lamp? I am wondering why you gave all the rear view mirror info?

The original problem was rear view mirror switch was bad. After replacing one, and it immediately blew, I started to check. Turns out that I am getting power to the outside rear view mirror switch from 2 power sources, where it should be only one. If I remove only the fuse for the power mirror circuit, I still have power to the switch. If I remove the courtesy light fuse only, I still have power. I checked last night, and I believe I am getting power back fed into the circuit from the dome lamp. If I remove the dome lamp, all is well. If I install the dome lamp, I am back to two power sources to the mirror switch. Interesting note to add, the reading lamps on the inside rear view mirror do not work from the switches on the mirror. They will go on with the door open, but with door closed, and after the timer times out, you cannot manually turn them on. Back to your question, the dome lamp should come on when the door is open, or with the dimmer switch on the dash. And no, the other interior lights behave correctly. I am still tryin' and I do appreciate the replies!!!!

They share a ground somewhere. That ground is loose or corroded. Therefore power is coming _backwards_ from the ground point back into the lamp because the ground point is several volts above ground. Look for ground points.

--scott

Normally the wiring that goes overhead goes up the A-pillar. Im guessing it does that in your vehicle too. There is only need to bring a single ground overhead.

I don't have the schematic so im going off general knowledge here (automotive systems engineer for 10 years). The dome lamp and the mirror lamps are both connected to ground through the ajar switches. When the ajar switch is open (door closed), you essentially have +12V on both side of bulbs. Since the other side of the mirror bulbs is the dome bulb, this will look like two sources of power, but its reall not. Try checking when the ajar switch is closed (door open).

Technically if they share a ground they should be from the same Fuse. If its not then its a bad design, but thats beside the point here. Maybe you can double check though that the two appearant power sources are from different fuses.

Also power mirror fuse likely is unrelated to rear view mirror feed.

You should have 3 wires in your rear view mirror. One is 12V from a B+ fuse. One is a ground. One is tied to ajar/dome switch. Check that each of these is working.

I didn't follow your statement about what happens when the dome lamp is installed and it being dim. Did you mean to say when dome lamp is installed the mirror lamps lit dimly?

It looks to me like your problem is the ground wire to the rear view mirror is cut, or maybe a terminal has pushed out of the connector. Or maybe its another bad mirror switch.

All is now well! Finally got my hands on the factory schematic, and traced the wires, looking for the bad ground. Well, it turns out that the INSIDE rear view mirror, that had reading lamps installed is what went south. When the fixture went bad, it back fed power thru the loom into the OUTSIDE power mirror switch. Dont know how, but I replaced the INSIDE rear view mirror, and all is well.

Again, thank you to all that responded!

sometimes these electrical problems are a real bugger. If you think about it, a modern vehicles is 30 times more complicated than your average household. Maybe 100 times more complicated. No exaggeration.

I becomes 1000 times more complicated when you don't have the wiring diagram for YOUR vehicle, but just a generic POS like in Haynes and Chilton. Then you're really on your own.

It took me months to hunt down an -intermittent- alternator failure. Emphasis on the word intermittent. Usually by the time I got under the hood the problem was gone.

Why was my battery losing charge over time? Needing to be recharged every few months? Never an idiot light. Only recently when the idiot light began coming on frequently and STAYING on did I have a chance to grab this problem by the horns and take the bull to the ground.

Now I know, it was an intermittent electrical contact at the voltage regulator PLUG on my alternator, which has an internal voltage regulator BTW, but that is OK. The connection wasn't.

I'm still having trouble with that. I get the dash light for alt/battery, lift the hood, press down on the plug, the light goes out, the voltage comes up, I go on my way.

What it comes down to is SHIT PARTS.

Now I am going to *coat* the VR terminals with SOLDER just to enhance their diameter, cleaning any flux of the surfaces after the solder hardens, and jam that fvcking plug on there with a hammer.

Now imagine, I used to have to fly to Dallas Texas to deal with

The nightmare continues. I think I'll do this repair in the driveway where I can see what I'm doing. Because you know, the pins are vertical and the solder is going to want to puddle at the bottom and short the pins.

Life's a bitch, and then you die.

Lg

Try some DeoxIT contact cleaner and rejuvenator. Works wonders at making electrical contacts reliable again. I use it on everything, light bulbs, batteries and all over my auto and RV. Don't have a boat - almost wish I had. Nope, not really. I guess I will tell my neighbor. They have a great website

Now you tell me. What I did, was melt some solder on the 3 spade pins coming out of the voltage regulator. Not a lot of solder, but enough to give the pins

So like I said I was going to do, I got a screwdriver and a sledgehammer. No joke. I put the handle of the screwdriver over the connector, and whacked the blade of the screwdriver with the sledge to

Voila. You can't move that thing if your life depends on it ;-\ It is fully seated, and is held in place with solder that extruded in and around the female metal contacts in the plug.

I started the engine, and yanked and pulled and pushed on the connectors and wires all which ways, and it isn't moving, and my voltage is rock steady from the alternator. NOW I trust it to give to the wife. Before this moment of truce, no. Now, yes, I deem the vehicle fit for road service.

I still get back to the same conclusion. shit parts. What other explanation is there? Ford is trying to save 3 pennies on one of the most important connectors under the hood? If they are cheaping out the vehicle there, what else don't I know about yet?

I will look for this DeoxIT next time I visit radio trash, but my experience with *contact cleaners* is they are short lived, especially in harsh environmental conditions. I think this metal extrusion process helped along by a sledge hammer is probably going to last for the long haul.

Lg

Sounds good. Give DeoxIT a try, you will be surprised. I have tried just about every cleaner out there and this one realllly works. They make a product, Deoxit SHIELD and GOLD, that are used in severe environments. I have used the deoxIT GOLD on my audio system with amazing results - I actually heard a difference in the audio - seemed clearer and crisper. The SHIELD is supposed to be for outdoor and other severe areas - haven't tried it yet. If it works as good as their other products I would try it also. Mike

Thanks for the tip Mike. I will look for it today. I am in the process of really ramping-up my emergency car repair kit. This should definitely be in the bag.

Lg

There is a company in Highland park "HELM" that we order electrical service manuals from. They contain very good schematics, Usually created by the OEM. I like to have one for each of my current cars.

I designed automotive electrical systems for the last 10 years. They are quite complicated. Today they are becoming increasingly networked. I had the 1996 manual and drive a 1995 that died, but both could have been different from the 94 which I dont have.

did you check that its actually not "back-feeding" power now? Glad to see it fixed.

Which means, essentially, my wiring diagrams are worse than useless. As I have found out from first hand experience.

As a side note: There are sensitive microelectronic components in a modern vehicle which will not take *kindly* to a superimposed radio frequency tracing signal. In retrospect, using an RF fox/hound to trace wiring under the hood of a modern car is a recipe for disaster.

I did some experiments, but the net conclusion I have to come to is that RF will kill your engine computer components in a heartbeat. But I used to have a low voltage LOGIC PROBE, which consisted of a low voltage signal injector and detector. This is what I need to use, but then you have to go point to point on every freaking connection, and if there is a short, you don't get any signal at all.

Take an example. I put a low voltage *pulse* ( call it a square wave ) on a wire. I can't pick it up anywhere. Is it because the logic circuits won't let it through or is it because there is a short somewhere. Nobody knows. Ergo, useless idea.

Logic probe, no good. RF signal tracer, no good. Final solution, bang your head against the wall and use a DVM. Outside of special expensive test equipment available only to Dealers ( because of the cost if not the proprietary nature of the things ), there is little left for the folks at Larry's Car Barn to use for diagnosing electrical problems.

Lacking the *proper* expensive test equipment, and a set of accurate wiring diagrams for _my_ vehicle, it is something that is turning my hair gray. Too many computers under the hood, programming that I know nothing about...I am left at the *sensor level* and once a wire enters a wiring harness to join up with 600 more wires that look just the same, it's gone. Lost in the crowd.

There is nothing about a *modern* vehicle that is simple. Nothing at all. Which is why I have taken an interest in the subject. Math used to amuse me, but for lack of practical applications, I lost interest. At least vehicle repair and maintenance has some social and moral redeeming vale.

Lg

Not really. Electronics tends to be sensitive until its constructed into some component. After which it tends to be resilient.

RF should not damage an engine controller. Its the most robust module in the vehicle. They endure many tests including RF injection, and many are require to operate through it. Some tests the module can fail during, but it must recover if power cycled.

Well it depends on the circuit type. It may be pulled to ground through a resistor, or pulled to b+ through a resistor. Or it could be a network circuit, or some other electronically controlled circuit that will fight your pulses.

Also on modern vehicles you may end up picking up the bus pulses. The ntwork can be awakened by many things like opening a door, inserting the key, opening the hood, etc.

Well thats why I have the electric manual. The circuits are all color coded so you should be able to trace them. The connectors have numbered or lettered pinouts as well. It takes a bit of getting used to the manual.

Well you can get a OBDII tester for about as much as the manual. You really cant test the cars much without the obd2 tester because the computer will sometimes compensate-away your attempt at testing.

without tester or manual, you are pretty much dead in the water.

On the bright side, the electrical systems are more computerized, but tend to have fewer components and are more robust than in the past. Some OEMs are better than others with this. Honda has shared electrical parts across car platforms for at least 10 years. Chrysler is by far the most agressive and is basically the leader in adoptine new technologies. 1996 grand cherokee was one of if not The first us OEM to use network work bus line in the vehicle. Ford will get to it eventually, and GM has great ideas and strong plans and tends to get it right when they finally get around to doing it by which time chrysler will have it right through brute force :P

Your low end cars tend to still be basic wiring though as while the electronic systems can be more robust, they cost more unless enough features are present to support them.

Ill take my old 1982 chevette though over one of these new cars. It may break down a lot but everything I need to fix it I could carry in a single tool box :)

Hi,

Yes I have an OBDII tester. It is of limited readout possibilities but nevertheless is a hell of a lot better than nothing ( Actron 9145 IIRC ).

It is pretty good for what it does...but lately I have been thinking about going with AutoTap. The reason I don't is because I don't need that _level_ of diagnostic capability at this time. And I don't have a portable computer anyhow, just this desktop.

But I do have a Davis Car Chip, which reads any of 4 out of 20 variables every 3 seconds and records the data to the chip memory, which I can interpret on my computer in graphic form ( very useful when you have thousands of datapoints, and are looking for any significant deviations ).

My car is running fine at the moment. IF my old v-ribbed serpentine belt was slipping on the alternator pulley, it isn't doing that anymore. I just put a new Goodyear Poly V belt on the engine, and it runs slick as a whistle, even when the air conditioning compressor cycles on and off.

So I think I got rid of my problem by replacing the serpentine belt AND by providing better continuity at the alternator voltage regulator connector plug. Time will tell, but so far so good. I did a leak-back check of the diodes in the alternator and they are someting like 20 MICROamperes. Not enough to notice.

Then I got behind my dashboard and got hold of any wires that could short out at the accessories socket and separated those, and went through the wiring from the steering column and the inside fuse/relay panels. Everything looks *ship shape* at the moment, but since I put the new Goodyear Gatorback on the engine, I want to take the Davis Car Chip in the house now and download the voltage data. Since I installed it, I want to see a nice smooth even alternator output.

So excuse me while I am off to grab my *flight recorder* chip. then I will later program it to look at long term fuel trims.

OBDII is great. I can't Imagine how anyone can get along without it...they would need a front seat full of gauges and electronics.

Lg