Wiper circuit resistance OHM My!

[rasouth]

I am having problems with my front wipers not working. I have tested the MFS a number of times off the car and on a work bench, getting the correct readings... 46.7k ohms, 11.3k ohms...
My question is has anybody tested the MFS while still in the car and hooked up? When I did this my readings were nowhere near what I expected. I got around 8-10k ohms no matter where I had the switch turned to, i.e. off, low, high.
Let me back up for a minute... I have performed all the basic tests of checking fuses, checking relays, switching relays, motor, connections, continuity between each item, replaced MFS, swapped out the GEM with identical number-matching GEM. I have an OBD2 adapter with Forscan and during the GEM test everything works... wipers, doors, lights, rear wiper, etc. That tells me that I am getting an output signal from the OBD2 adapter to the input side of the GEM (if that makes since... I work with computers a lot) The only thing left out of the loop is the MFS.
If I unplug the 26-pin wire harness from the GEM and test the MFS at the harness I get the correct readings...46.7k ohms...
Now back to my question... Has anybody tested the MFS while still hooked up and plugged in using the three metal tabs that correspond with number 13, 14, and 15 tabs of the MFS?

 

[koda2000]

Just a thought... In my experience with weird electrical problems that don't seem to make sense, bad grounds can be the problem. Have you checked the ground on the firewall next to the PCM? There are also 2 ground wires from the body to the frame that are found about midway down the outside of frame rails. These two ground wires (they're the braided kind) often rot away, or they can get snagged on things if you off-road. IDK if there are any other body grounds, I've never noticed any, but make sure these grounds are in place and have clean rust-free connections.

 

[CDW6212R]

If you are testing wiring inside the vehicle, use the main body ground points for reference. Those are behind both kick panels, the 8mm green bolt with several wires leading to them. If you suspect grounds or test them for a base test, check between the kick panel grounds, and the battery, PCM, and radiator support grounds. All of those should test to be same, thus the kick panel points are trusted grounds.

What kind of MFS have you swapped in so far? Was it a trusted brand, new in box part, proper model part? The 96/97's take different parts than 98-01's. I have a Motorcraft MFS I bought "new" from eBay for my Crown Vic, which has a left turn signal failed circuit in it. I can force the left signal by barely moving the MFS, but all the way on it doesn't work. So a "new" part isn't a sure known good part.

 

[J_C]

If you short together (jumper wire or paperclip, etc) the pins on the connector that correspond to the MFS pins that measured 47K, (ignition key used of course), the wipers should come on at high speed. Similarly if you set the MFS to high speed, the pins that read 47K should read close to 0 ohms with it unplugged.

In the former if the wipers come on it suggests a bad MFS. If they don't, and the MFS reads close to 0 ohms set to high speed, probably not the MFS.

Since you were able to get the wipers to work with the scan tool, I would then wonder if the wiring to the GEM or the connector itself is damaged.

Seems like I saw a post in this forum some time ago where someone had one or more contacts in the connector pulling out the back and they had to devise some way to keep them in, maybe with hot glue on the rear or something?

If it's a wiring short or frayed/break, it could be dependent on the positioning of the wire, could come and go by moving the connector around or tilting the steering wheel.

You could also check resistance at the other end, between the corresponding GEM pins on the connector to it, withthe MFS plugged in set to high and unplugged, connector unplugged from the GEM, and check resistance from both to a chassis ground.

 

[rasouth]

A little more of what I have done so far. I have two MFS and both check out to be fine. I have two GEMs that, other than the wipers not working, everything else works, i.e. windows, locks, lights, rear wiper and washer, etc. I have replaced the wiper motor and checked all connections and ground wires, I have checked continuity between each and every connection, fuse and relays between the MFS to the wiper motor. I have back probed the y/w wire, (I believe that's the right one), and grounded it, and the wipers worked. I have used an OBD2 adapter and Forscan to test the GEM and the wipers worked during the test. To me that says that all the relays, fuses and connections are functioning properly. I have done this multiple times with both MFS and GEMs. It's just from the MFS to the GEM I get no signal, or resistance, to the GEM. I have taken the motherboard out of the GEM, hooked up the harness and I get continuity from the MFS to the GEM. What I don't get is the resistance reading of 46.7k Ohms. I get 8-10k ohms at the GEM.
What I would like to know is has anybody checked the resistance reading at the MFS by using the three metal tabs located on the MFS behind the turn signal handle and what those readings are.

 

[rasouth]

Really? Nobody has ever checked the MFS while it is still hooked up to steering column.

 

[J_C]

^ Why would we? Usually you just take it off, decide whether to clean it out or buy a new one, then put whichever back on and you're done.

I see three main possibilities. Either both of your GEMs have the same fault (seems unlikely since we're not seeing a rash of people reporting that fault so not a very common fault), you are doing some testing wrong and will need to step back and take a vacation from it to figure out what is going wrong, or you have a wiring or connector fault (probably the most likely).

You don't necessarily need that measurement. If you have the resistance measurement between any two pins with it unplugged, and you have the resistance measurement between the two pins on the gem that they connect to (with it still unplugged) then a parallel resistance calculator should tell you what the resultant resistance is.
Parallel Resistance Calculator

I am not clear on whether you shorted together the two pins corresponding to the 47 ohm reading you took previously or not, but that should turn the wipers on if everything besides the MFS works. If you are getting 8K-10K at the gem (why this variance, it is odd?) that is still within the resistance range at which the wipers should come on between low and interval mode.

Have you yet tried completely reinstalling the MFS, with it mounted and steering wheel in the right position so the wiring harness is not in an odd position, and THEN measuring for resistance at the GEM corresponding pins as well as trying to run the wipers?

 

[J_C]

It is just bad lighting or is the light blue/orange wire on the connector burnt? It looks dark right where it meets the connector in your picture.

 

[rasouth]

Bad lighting on the blue wire. By grounding out the yellow/white wire (I believe, I'm going off memory) the wipers do work. I have taken the MFS off, tested it, put it back on, replaced it and still no wipers. All the tests I have performed were done many times over the last year or so and things point to the GEM, but, like you said, seems unlikely that both GEMs are faulty. As for the 8-10 ohm reading, that is with the wiper switch in the on or off position plugged into the GEM. Unplugged from the GEM I get the 46.7k ohms. I don't think I am doing the tests wrong. I've got multiple schematics listing every fuse, relay, connection, harness, etc. I checked every connection from the MFS to the motor itself. I might be missing something but I don't know what. I was just curious as to if anybody had ever checked the MFS while it was still plugged in.