the wire that is broken may be the shielding on the wire , not be the wire , and didn't notice the single wire with it or insulation of it.

 

that makes no sense at all.

 

The other end has a connector with 3 wires connected two white and green wires and a red wire with a black wire coming out of the connector but cut off not connected to anything. How come there are 3 wires on one end and two at the other.

 

the third wire into the speedometer is power. the blue-red wire is power from ignition switch pin 15R. the green-white wire is the speedo signal, and the brown-white one is the twisted ground wire that came from the speedo, this is grounded inside the speedo.

(These colors are from my 1992 greenbook, different years may be different)

the green/white and brown-white wires also go to the ABS controller, but at least in 1992, they are split off at one of the bulkhead connectors before it gets to the instrument panel.

 

Hey Lev and pierce. Long time no trouble. But now the speedo needle on my old, runs-so-good 1990 740 GL (yes, my 740; my son has my V70 on perma-loan) is sitting there twitching at 0. First sign of trouble was when I noticed that the trip meter wasn't working, when I was trying to see how my new old car was doing on MPG (!); couldn't get it to work consistently (then at all). Then I realized the odometer wasn't moving either, and then I did the math and realized that maybe it never really has been working since we got it from the last owner (I did catch it moving one time, though, one of those times that I got my trip meter to work). And now the speedo has stopped.

The way the needle is lying there twitching at 0 reminds me of how the temp needle would dead-twitch before I changed the coolant (with your help), which temp needle now comes to life quickly and consistently (almost like I revived the sensor after long dis-use sitting in garbage coolant). So is this a sensor problem? Or is it more likely those ancient capacitors in the instrument itself?

Thanks for hearing me out. (PS. No bull****, the education I got from you guys, especially Lev, more than brought a dead car back to life, it gave me a new lease on life too.)

 

Check the pick up sensor and wires at the differential but it's most likely the spedo, yes, the capacitors... PIA!

 

Hey Lev. Cool to hear from you. Haven't gone back underneath the car yet... I don't have to take apart the differential (aka the pumpkin?) to see all that stuff, do I? If so, wow could I use another one of your walk-throughs...also if/when it comes time to pull out the instrument cluster...............

Does the "progressive" failure of that instrument (i.e., at first, speedo was working even when trip and odo meters weren't) point to failure of the instrument itself being more likely?.....

 

Yes, sadly the chances are it's the speedo, not the diff. sender where the speedo acquires its signal. But common sense to eliminate the easy one by looking at the diff. The sensor and associated wiring are there and exposed, easy to see if there is an issue, no need to go inside the diff.

 

Hey lev. Good call re: checking at the diff. Wiring to sensor claimed by the rust! Now I need to know what to do here at the box??

 

The speedo sending unit is in the rear differential housing. Check that the wires are not broken.

 

This guy has wire harness parts for old cars.

https://www.prancingmoose.com/blackvinyl.html

 

Too much mumbo jumbo!! Give the man what he needs!!! I have plenty speed sensor wire ends available ready for shipping!! Oem excellent quality
just send me a private message brother.
your problem is not in the dash like these cats keep saying...
The evidence is in your hands
Goldenblock

 

When I had this problem is was the instrument cluster, the solder had become compromised and my mechanic resoldered the entire cluster.