Speedometer Voltage / Speed Sensor Question : V-Twin Forum: Harley Davidson Forums
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Old 04-23-2008, 05:34 AM   #1 (permalink)
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Question Speedometer Input Wire Voltage Question/Problem

Does the speed sensor input wire (White Wire) coming out of a '96 - '03 electronic speedometer supposed to carry voltage? (even when not connected to the sensor?)

Background: I recently purchased a "new" 5" H-D Electronic Speedometer model # 67178-95A dated 6/25/96 originally made for an FXDWG from a Harley Davidson Dealership online to replace a cable driven speedo on my '97 CMC Softail.

Looks like this:

I simply wired 12v+ from the bike to the Orange wire and Grounded the Black wire and so far all seemed to be ok. The bulbs of the speedo came on as soon as I turned on the the switch, and the digital LCD showed the miles at all zeros and I was able to switch back and forth between the odometer and trip meter functions. I wasn't using the Green/White Wire for the turn signal cancellation as I don't need it so it remained disconnected. So far all was well.

I then mounted a new ThunderHeart Programmable Speed Sensor to the transmission. (Can correct any speed imbalance due to signaling changes from an altered gearing ratio or tire size than what the speedo was calibrated for.) After wiring it up to the 3 pin triangle Deutsch connector coming out of the speedometer to the speed sensor (Red 12v+ Speedo Wire to Red 12v+ Sensor Wire; White Speed Input Speedo Wire to Green Speed Output Sensor Wire; Black Ground Speedo Wire to Black Ground Sensor Wire) the Programmable portion of the speed sensor was not responding. It is supposed to flash a red LED on the sensor housing once each time it is turned on. Nothing... not even when trying to enter it into programming mode. Obviously I thought to check my connections.

All looked good, so I broke out the multimeter. It showed the sensor was getting power where the sensor and the speedometer were connected. (10+ volts out of the red wire - Sensor runs on 9v to 14v). BUT also showed 7.xx volts coming from the White Wire (Sensor Input Wire). I disconnected the sensor from the speedometer and reread the meter on just the speedo wires. Same outcome. I have around 7.5volts coming out of the White Wire. From what I understand, that wire is not supposed to output any voltage, only intake 1v to 12v from the Sensor. Which brings me back to my original question. Does anyone know whether or not for sure that the Speed Sensor input wire on the Speedometer supposed to output any voltage? (Indicating possibly that the speedometer has an internal circuit/wiring problem.)

I have since called the Harley service dept. at the dealership I bought it from and they don't know the answer, my local dealership doesn't know the answer, and I've even called Thunderheart and explained to them my problem and their reply is that they don't believe that the input wire is supposed to carry voltage like that... but no definate answer. I have a Clymer H-D repair manual that says nothing much of the connector and the wiring diagram only shows where it connects to. (Don't yet have a Harley Manual as my bike is technically a custom build, wont ever completely match an HD model.)

As the story goes, I've since tried hooking up my sensor indoors to a 9v battery and although on the first day (probably 20 or so times) it didn't work, but the next day it did (oddly enough)... and still does. I'm even able to program it. I was initially afraid that the "stray" voltage from the speedometer input wires fried my sensor, but it now works.

As far as the speedometer, I can hook it up to a 12v battery indoors (off the bike, so its no longer a factor in the equation) and as always everything seems to function correctly (light bulbs, LCD numbers, odometer/trip meter switch) but when I put a multimeter across the White sensor input wire to Ground I get around 7v. Just as a test I took the bulbs out, and hooked the speedo up to a 9v battery, and the White wire registered about 4.5v indicating its somewhat proportionate to the main positive voltage.

The reason I'm trying to find this answer is that I need to know whether or not I will need to look into returning and replacing this with another one as its technically non-serviceable. I am also not too keen on testing it out with my programmable sensor now that I know for sure its working as I'm afraid it could possibly get damaged (again?) I don't have a regular sensor to test with as I'm converting over from a cable driven speedo. I was also not able to ride the bike at the time I had both the speedometer and sensor mounted to test if it did anything anyway, as I have the frame on a stand while making other modifications and repairs.

I've searched this forum for hours looking for a similar problem/solution and have yet to find one. This would be my first posted question as I've always been able to search and find pretty good answers to my previous questions. I don't know of anyone that has an electric Harley speedometer of that year-range/type that I would be able to test to see if they have any voltage coming off the sensor input wire of the speedo while powered up. Maybe one of you would be able to do that for me. And if you've made it this far, thanks for taking the time to try and help. I've tried to provide as much relavent detail as I could think of at the moment. If anyone needs any other info, let me know. Thanks again.

Last edited by WolfGrave; 05-05-2008 at 03:53 AM. Reason: Added Image
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Old 05-02-2008, 06:17 PM   #2 (permalink)
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Lightbulb Question Answered / Problem Solved

Short Answer: Yes, the white speedometer sensor input wire is supposed to carry that amount of voltage.

After rebuilding the rest of my bike I had to make a decision concerning retrying the speedometer. I talked to another tech at my local HD shop (Chris at Bumpus in Jackson, TN - Extremely helpful in attempting to troubleshoot my problem.) and we attempted to test it with a speedo tester. Even though it wouldn't work unless we connected the sensor leads in the wrong way, we got it to work. (but at times erratically, we had once programmed it to accelerate to 110mph and the needle decided to go counter-clockwise from 0mph to get there.) So at best I was left with a "Good-Luck", while knowing that its a posibilty to work.

I decided to just try rehooking it all up on the bike while potentially risking damaging my sensor. Low and behold the sensor powered on while connected to the speedo. I then tried rotating the rear wheel and could see the speedometer needle move correctly as well as the LED on the sensor flash with every turn of the transmission cog. Thought to recheck the voltage on the sensor speed data wire to see if anything was different and once again I have about 7 volts. It fluctuates with the pulses as the rear wheel is turned. So seemingly its supposed to operate this way.

It is now apparant that my speed sensor was initially at fault and in searching for culprit I found an unaccounted-for voltage coming from my speedo input wire which I thought could've been the source of the problem which in turn prompted the question on this forum. Conclusion: The wire is supposed to carry it's own voltage. Case closed.

Thanks to those that read my question in attempts to try and help. Judging by the lack of responses it seems to not be such common knowledge as its not a common problem. This seems to be the only thread of its kind on this forum so maybe it will help to serve anyone else in eliminating this small variable when troubleshooting a similar scenario.
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