98 Blazer Help Understanding Wiper Circuit

The issue with the wipers on this truck is they operate at about 50% - 70% normal speed when they are on LOW or HIGH. Also, when you go from the OFF position to a PULSE position the wipers will not operate until you first switch them to HIGH and then back down to the PULSE position you want. Been like this for a long time and the multi-function switch was replaced with a new one due to an unrelated issue about year ago. Even at that time there was no effect on the wipers (better or worse). Before I replace the motor I wanted to check wiring and circuit integrity. I started off with a ground to ground voltage drop test (KOEO wiper selector in every selected position). Back probed motor connector GROUND and used B(-) for the other lead. The max volt drop I got was .15 volt which I believe is well within tolerance? Referring to the TSM, is stated I should get battery power on the YEL, DK GRN and GRY wires in PULSE mode. I disconnected the motor connector and with KOEO measured, selector in the first PULSE position (lowest setting) 11.86 at YEL wire (battery voltage), a little less at DK GRN wire and about .75 volt less at GRY wire. As I increased the selector setting the voltage on the GRY wire did increase.

I have questions concerning the resistors in the multi-function switch. I had come to understand that if there is only one resistor in the path, there would be no voltage drop due to the resistor? Since the connector was unplugged from the motor, there was no other resistor in the direct path. What am I missing or not understanding? The TSM states I should get battery power from those three wires. It does not state anything to indicate there would be differences in any of the wire voltage due to the position of the switch when measuring the power.

Please help me understand. Thanks much!

If you have a integrated pulse board on the wiper motor, I would removed and check it for cold solder on the board. If you have it that would make the electronics inside fail to work properly.

Thanks for the tip, I will definitely take a look at that. But I am also trying to understand the circuitry before the control logic. With the connector disconnected at the motor (so not connected to the control logic at all), shouldn't I read battery voltage on the GRY wire regardless of what pulse position it is in? Since at each position there is only one resistor in the path (at the multi-function switch) shouldn't I read the exact same potential on the GRY wire that I have on the YEL wire? Instead of the potential rising as I switch to a higher pulse position? Again, thank you for the tip.

Okay, let's try this: I imagine you are using a digital multimeter with at least 10 mega ohm input impedance. If you disconnect the windshield motor assembly, ignition key in acc or run, move the speed selector to the 680K you should measure B+ voltage at that point or point E at the connector as well as C on the same connector, as long as E5 on connector C211 is not corroded. This happens because the high impedance in your meter you did not allowed current to pass, but if you use an analog meter, then you will see the voltage drop. Thank you. I will see if I can find a picture of your control switch.

If your problem is that circuit board, this may help you if fits your truck...
www.amazon.com/Dorman-Wiper-Pulse-Board-88136/dp/B0002JMU3E

I'm a little confused here, so please bear with me, and correct me if I'm wrong please.

I understand where you're coming from, that with the wiper motor disconnected, there should be 12v on the grey wire regardless of switch position because no current flow=no voltage drop.
But, isn't the yellow power wire in the same connector?
Meaning, with the connector disconnected, there would be no power going to the switch. So I don't see how you are measuring anything on the grey wire with the motor disconnected, unless, your are maybe measuring on the motor side of the connector and not the switch side?

hello, if you look at C203 the yellow wire splits going to C211 and the logic board. It looks like one connector is inside the cabin and the logic connector that holds the yellow wire at cavity C is by the wiper motor, I can measure those voltages by disconnecting the wiper connector and testing at cavity C and E. The only problem I have with that diagram is that the motor should be fed by the logic board where I think you have a relay. Now if you disconnect the logic board and does not get the B+ voltage you are measuring somewhere between component and the wire is short to ground somewhere. It is the only way I can see a voltage drop on the circuit. Sorry for the confusion.

I see, I was thinking he was making measurements at c211 with the connector unplugged.

Sorry for taking so long to respond. Today is first day back on puter since my last post.

Castironman, I believe you and I are saying the same thing, that with C211 disconnected (KOEO) I should not get a voltage drop (measuring at C211) on the grey wire regardless of the PULSE position on the multi-function switch. This is what I initially wanted to verify. Just to note, the multifunction switch controls the turn signals, wipers, hazards, washer pump and cruise control.

Noah, C203 was left connected and is inside the cabin behind the knee bolster. So constant B+ is supplied (KOEO) through the YEL wire. When putting wiper switch in PULSE mode, there is also supposed to be B+ on the GRY and DK GRN wires also (once again measuring at C211 disconnected (harness side)). However, on the GRY wire I am getting a voltage drop as high as .75 volt when compared to YEL wire.

Because this was driving me a little batty, and due to my level of understanding circuitry (novice at best), I went online and bought a little electronics kit that included, among other things; a breadboard, various resistors and wires to work on the breadboard. I created a circuit similar to the multi-function switch wiper circuit. I was curious to know if there would be resistance due to the resistors sharing (but not in series) the GRY wire. When I set the circuit up I found there was no resistance when measuring in the various positions. Not until I added another resistor (acting as resistor in the control logic of the wiper motor) in series to one of the other resistors did the ohms measure up.

If I am correct, this confirms to me that regardless of the PULSE position of the switch (not counting the OFF position), at C211 (disconnected, KOEO, harness side) I should be measuring the same voltage as I do on the YEL wire. This leads me to believe that somewhere in the GRY wire there is a resistance (corrosion, worn covering touching one of the other wires, etc) that is acting as an unwanted resistor in series with the resistor at each position PULSE position the multi-function switch.

My thinking is that replacing the circuit board in the wiper motor would not solve the problem because I would still not be supplying the correct voltage the motor logic is expecting through the GRY wire. Thoughts?

And thank you very much for bearing with me (did I use the word resistor enough? ). I really want to understand circuitry and what is right and what is wrong before I replace parts.

Did you get any where with this one?
I've been waiting for an update

There's no reason I can see for voltage to drop on that wire, unless like you theorized, there is some kind of resistive short to ground before your test point. Or maybe (long shot here) a cheap multimeter with not enough internal resistance, but I've never had a meter to that significantly dropped voltage on a 12v circuit...
You could disconnect c211 and the wiper motor, then check the grey wire with an ohm meter to see if there is any continuity to ground.
Thinking of the symptoms, you say that the wipers only work at 50-70% speed on high.
High is a direct circuit to full battery power. I would check power at the purple wire, and the ground at the motor with everything connected and wipers running.

Noah wrote: Did you get any where with this one?
I've been waiting for an update

Hi Noah, haven't been back on the truck since my last post a couple days ago. I really appreciate your input and am going to run back through tests with the wiper motor running again to see what that turns up. Then I think I'm going to go ahead and disconnect C203 &C211 and see if I get any continuity between separate wires and also ground for each one. If I get any, then I'll at least have it nailed down to somewhere in the harness. Finding the short to power/ground/neighbor will be a completely different "pleasant" experience. Also, I'm using a really good Fluke 115 True RMS meter. Thanks!

Something interesting that I believe isn't right? In the garage tonight to do some tests. I disconnected only the connector at the wiper motor, KEY OFF, using a PPIV to check the connector (harness side) to insure got ground on black wire, but expecting nothing (ghost voltage) on the other four wires. Not powering PPIV with the switch at all. Just touching the harness side connectors to check for any reading. As expecting BLK wire gave me solid ground tone and green light, display showing 00.00v. Good. DK GRN, PPL, and GRY all show no reading, no light, no tone. Good. Then I touch YEL wire...for a half second I get a ground tone and green light then it stops and display shows 00.16v to 00.21v. I do this several times and keep getting the same result on the YEL wire. Quick ground blip and light, then it stops and display shows around 00.18v. Correct me if I'm wrong, but I shouldnt get anything on the YEL wire? Just like the DK GRN, PPL and GRY wire....correct? Note, the key is OFF. I'm measuring at the motor connector (disconnected) harness side.

Then I pulled IP fuze #17. Measured YEL again and got what I believe I should. No blip of tone, no light and the display was blank. I believe this means I do have an issue, but it's obviously further upstream from IP fuze #17. Could someone confirm that I shouldn't be getting that quick ground tone (and green light) and then the 00.18v on the PPIV display on the YEL wire. Please confirm that I should get no reading/tone/light at all? Thanks much.

Here is the power distribution to IP fuze #17. Now I'm really unsure if what I got on the YEL wire is supposed to be there or not. Whole lot of junk connected to that feed wire (to include the RAP). But still fuze #17 is supposed to be hot only in ACC or RUN....and I had the key OFF.

The ground blip and 00.18v reading on PPIV stopped when I pulled the RAP relay. Not sure why the RAP relay would effect that YEL wire and produce a ground at all. Would it be safe for me to try my wipers with the RAP relay removed, just to see if they work at a normal speed? Won't be able to for a few days because the RAP relay is buried behind the dash and I have to put the truck back together for now.

I wouldn't read to much into the readings you're getting from the power probe on the yellow wire from the wiper motor connector.
That diagram is real small on my phone, but the circuit also includes that relay which is shown to provide a path to whatever those other components are (sorry, can't make them out) while in the rest position.
That's probably why taking the fuse (and the relay) out of the circuit shows open circuit voltage.

I really like my power probe 4, you can hammer through a lot of problems with one. But you can also end up chasing your tail.

So I ended up replacing the circuit board and didn't not get the result I was hoping for. It was a little bit better, the speed seemed barley perceivable better in LO and HIGH. However, when starting in pulse mode (without first selecting HIGH and then dropping back down to a PULSE speed), the wipers did not start intitially until what I would consider the "2nd wiipe". Meaning, turned the wiper to the first PULSE mode (slowest), nothing happened. ~21 seconds later, the TSM stated time span for between wipes, the wipe happened. This struck me as if on the initial turn-on there was just not enough power to start the wiper. I was at first thinking that maybe the motor itself is just "weak" and needs to be replaced.

Then last night I was playing with my new Maxisys (thank you to those that helped me choose the tool) and found a BCM DTC stored in history. On my truck this does not set any MIL lights so I didn't even know it was there. The DTC is B1477 (Retained Accessory Power Circuit Low). Referencing the former post where I described what I thought to be a weird reading on my PPIV when measuring the YEL wire, I am now wondering if there might be something to that after all?

My thought process is that since the PPIV would have that half second ground blip on the YEL wire, maybe there is some initial noise or junk or something that is the reason the wipers wouldn't immediately start in the pulse mode until the "2nd" time for them to wipe. Since the YEL wire does (upstream) split to include the RAP, that there may be some connection. That maybe the RAP is pulling down some voltage in the YEL wire that should be going to the wiper motor? Not a whole lot to be really perceivable, but just enough.

I've already done some reading on the B1477 and when I get a chance to dig back under the dash I will look into the troubleshooting on it.

Any thoughts are welcome and I hope i have not bored everyone too much. Thank you.

When you touch on the yellow wire with the power probe and the key off, it's acting like an Ohm meter. So it's finding a path to ground through the rest of the circuits from in front of the fuse. That's why you are getting the momentary green LED blip.

I still don't have a good answer concerning the voltage readings you observed on the grey wire with the motor disconnected running the wiper selector through the modes. I would Ohm check that wire to ground on both ends with the motor and switch disconnected. A check on one end would likely be sufficient, but what's another couple minutes on your own truck? The only acceptable reading here is OL Mohms. (If your fluke doesn't have auto ranging, make sure it's set at Mega Ohms).


Next, I would set it to high with everything connected (and running) and check voltage at the wiper motor connector. At the purple, grey and yellow I expect battery voltage, the black wire ground voltage, and something else on the green wire. (Lol, sorry, not taking a shot at that. Somebody want to do the math? 12v, 24 kohm resistor?)


After that, the only real checks left in my eyes are for mechanical binding in the wiper transmission or arms, then time for a new motor. I suppose you could measure the current draw of the motor, but I couldn't tell you what to expect from a good or a bad one.
I hope this helps you out.
Sorry for the delay in getting back to you.

I was just thunking logic control assembly it has selector switch as an input

I believe all your inputs and outputs are goig through the logic assembly this tells me its a wonky logic assembly the logic is skewed somehow maybe got moisture in there

Thanks Noah, I'll try those tests out. Appreciate very much you taking the time. Chief eaglebear, I did replace the wiper circuit board and there was no change. Thanks much folks. As soon as I get back on this I'll let you know the results. But more and more I'm thinking the motor is slightly binding. Of course on the other hand, there's that B1477 in history I need to look into.