Speedometer and Headlight Phenomena

I am posting this same info on Yahoo's Mopar group and Allpar. I have
posted multiple questions at various newsgroups with regards to my
speedometer problems, so I felt it was appropriate to post back my findings.
I believe I have fixed my speedometer problem on the 1991 Dynasty. As you
may recall, I indicated that the speedometer worked intermittently. When it
was not working, turning the lights on bright seemed to make the speedometer
work. When the speedometer was working, turning the lights on bright often
caused the speedometer to quit working.

First of all, I want to let everyone know that I am not a mechanic, and I do
not have a complete understanding of the circuitry I am working with - I
made some "uneducated" guesses, and I believe I have fixed the problem.
However, at the end of the process, I have two concerns which I will state
below. If you have the same problem as me, it may be wise to give this
information to a mechanic and have them follow through.

Here is how I fixed my problem. Pull the pig tail connector off the distance
sensor which is located on top of the transaxle. Check the voltage of each
terminal with the car in the run position (car does not need to be running).
One terminal should have no voltage on it (the black wire with blue stripe),
and the other one will (the white wire with orange stripe). If you have the
same problem as me, you will get a different voltage reading on the white
wire depending whether your lights are on high beam, or if they are off. If
this is not the case, then no need to read anymore - this will information
won't help you.

I cut the white wire with the orange stripe right at the pigtail, and ran a
wire up to towards the battery. Beside the battery box, there is a big mess
of electric connections against the wheel well. A single bolt holds this
connector in place. Back the bolt off (you may have to slide the battery out
of the way). As you loosen it, it will "unplug" the connector. I believe
this is where the wires connect to the Electronic Control Module, but I am
not certain. Once you have this unplugged, you can pop the little black
cover off this connector (it has four tabs). You can faintly make out the
pin numbers on one end of the connector. Pin #47 should have the white wire
with orange stripe coming to it. I cut the wire near this connector, and I
soldered the wire I brought from the distance sensor onto this connector.
The next step is to remove the instrument cluster in the car. This involves
taking two panels off the dash. The uppermost panel comes off first - there
is a row of screws above the speedometer, gauges, etc. Removal of the
lowermost panel is fairly straight forward if you manage to find the two
bottom screws - one is in the very top part of the ash tray and one above
the emergency brake release. On the back of the instrument cluster, there is
a big, round connector. On this connector, you will find a white wire with
an orange strip. I cut this wire. I then soldered a new wire onto this
connector, and fished it through the firewall and spliced it into the wire I
had brought up from the speed sensor.

It took me a long time to diagnose the problem. My original assumption was
that one wire going to the distance sensor was a positive, and the other
carried a signal (square wave) back to the ECM and speedometer. This was a
bad assumption and it took me forever to realize this. It is the exact
opposite. The speedometer and the ECM both send 5 volts to the distance
sensor through the white wire with the orange and white stripe. The black
wire with blue stripe seems to be a ground, but without going into any
detail, I there is something "fishy" with this wire. I suspect the ECM and
speedometer monitor either the current spikes or voltage dips as the
distance sensor opens and closes the circuits.

Here are my two concerns:

1.. I know the white wire with the orange stripe goes to the ECM,
speedometer, and distance sensor. I cut the wire at all of these locations,
so I effectively disabled it. Does anyone know if this wire connects to any
other instruments in the car? I am concerned that it may be tied into the
PCM, and I may have disabled some other devices by cutting this wire. The
car seems to drive as per usual (but I haven't owned the car for very
long) - it has always downshifted from a hard acceleration rather roughly
and continues to do so; I have no idea if this could be related.
2.. After the following "fix", when I put a voltmeter on the white wire
with the orange stripe, I get a voltage reading of 0.2 Volts with the lights
off, and around 8 volts with the high beams on. Thus, something is shorting
to this wire. I don't like the idea of leaving a short in the car. I suspect
it is shorting from the high beam indicator because it does not work despite
the fact that the bulb is good - I also know someone with similar
speedometer problems and his high beam indicator is not functioning. Perhaps
the best solution is to find the power source for the high beam indicator,
and cut this. This may be a far easier fix for the problem than what I
posted above - however, without cutting all of the wires, I would have never
figured out what was happening. Does anyone know where to find the power
source for this indicator?

 

I get the impression you are working without schematics? That is like
trying to go from one town to another 200 miles away, not ever having
been there, having no roadmap, and not having any specific directions,
knowing only that it's "over in that direction somewhere". You are
having to make a lot of assumptions, only one of which may be necessary
to do some serious damage if incorrect - watch out for that cliff
ahead. 8^)

If you don't have a Factory Service Manual, either go to your dealer and
get them to photocopy the pertinent pages from the electrical schematics
section, or, probably easier, for $25 you can get a subscription at
www.alldata.com that gives you on-line access to the schematics right
out of the FSM for your exact vehicle, also there will be information
showing locations of the various connectors, sensors, switches, lights,
etc. Do not get an aftermarket manual (Chiltons, Haynes), as the
schematics in there are usually not specific to your vehicle, are even
labelled as "typical" for "similar" vehicles, and you might as well be
trying to use a map to Cleveland to get to Chicago - yes they both begin
with the letter "C", but they are not the same place.

Please get access to the FSM info. before proceding further and causing
more problems.

IMO...

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

I get the impression you are working without schematics? That is like
trying to go from one town to another 200 miles away, not ever having
been there, having no roadmap, and not having any specific directions,
knowing only that it's "over in that direction somewhere". You are
having to make a lot of assumptions, only one of which may be necessary
to do some serious damage if incorrect - watch out for that cliff
ahead. 8^)

If you don't have a Factory Service Manual, either go to your dealer and
get them to photocopy the pertinent pages from the electrical schematics
section, or, probably easier, for $25 you can get a subscription at
www.alldata.com that gives you on-line access to the schematics right
out of the FSM for your exact vehicle, also there will be information
showing locations of the various connectors, sensors, switches, lights,
etc. Do not get an aftermarket manual (Chiltons, Haynes), as the
schematics in there are usually not specific to your vehicle, are even
labelled as "typical" for "similar" vehicles, and you might as well be
trying to use a map to Cleveland to get to Chicago - yes they both begin
with the letter "C", but they are not the same place.

Please get access to the FSM info. before proceding further and causing
more problems. (With your having already posted your methods to other
forums, I have trouble believing that I am the only person to advise you
in this way.)

IMO...

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

Thank you for the advice - it is good advice and my warning at the end of
the email was probably not as blunt as it should have been. If you are
aware of any other places this white wire with orange stripes surfaces, I am
interested to know. As of yet, I have not been able to locate wiring
diagrams for this car (but will check alldata - I didn't know it existed).
I did have some info from someone on the internet, but it turns out that
their wiring diagram was in error. I actively sought out wiring diagrams
for my car before proceeding. I sought them on the internet, newsgroups, I
went to the local library, I went to both Dodge Dealerships in town, and I
checked EBay.

It seems impossible to find information on this car - but don't worry, the
guy at the Dodge service counter told me that their mechanics have this
information memorized - consequently, they do not keep manuals before 1999.
Interestingly enough, when I quized him on the distance sensor circuit, it
was plane that he didn't have it memorized..... The other dealership hasn't
been in business since 1991, so they have never owned these manuals. But
for $85/hour Canadian, they will fix your car.

Chris

 

You're very welcome - I'm certain AllData has the information for your
car available for a subscription. I think you will be pleased - you
will feel like you were blind and regained your sight once you see the
factory schematics (the proverbial light will go on). Your progress to
date must have been excruciatingly tedious.

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

I would recommend that you buy a Factory Service Manual for your car.
call 800-890-4038. They cost about $100 new or quite a bit less on
ebay if you can find one there. The FSM will give the wiring
schematic.
Later model year FSM's give the location of cable splices and ground
connections locations in the harnesses.
There are at least two other publishers of manuals that are a lot
cheaper but you get what you pay for so beware that any schematics in
these manuals may have a lot of errors. It really depends on how
much you value you place on your time whether you want to spend the
money for a manual or "hope and poke" for many hours.

If the voltage changes when the high beam is on then either you have
some shorted wires in a harness, or you have road salt in the large
bulkhead firewall connector, or what is most likely is you have lost
the ground for your instrument cluster. Unplug the instrument
cluster and see if this voltage still changes when you go to high
beam.
For years chrysler used a multi pole magnet and a reed switch as the
speed sensor on or in the speedometer cable to the cruse control.
Since I do not have a FSM of this year to look at I can not be sure
what your car uses.

 

Most motor vehicles use the Body, Frame, Chassis and/or Unibody for
electrical Ground. This is a cheap, lousey but common system that works okay
for X years and then leads to many malfunctions. Corrosion and bad
contact-surfaces are the cause of more than half of the elecrical problems I
find. " Bad Ground" is the most common problem. A salt environment (Winter)
makes it all worse.

Some recent machines use a Two-Wire system and/or FibreOptics. They have
potential for fewer corrosion problems. Maybe...

LS