Help me , gods of wiring

[ga.spyder]

OK...Here is a question for you wire nuts.I have the dash out of my 82 to install a 140 speedo out of a 79.That is the only year that the 140 speedo has a shallow face and the same cable(Ithink) Now ,I know the car wont go 140 but I am hoping it will think it can!The 82 has a yellow/red coming out of the speedo housing,that isnt present on the 79 unit.It goes to connector 28.Can anyone look at that wiring diagram and tell me what function the yellow/ red has and if I will lose that function with the 140 speedo. I will just leave the 82 unit in ,if this swap will create a problem.I have gotten better with reading wiring diagrams(really),but still cant quite follow the flow.Thanks guys,
Craig

[pope]

Craig,
this is where the wiring diagram is a little at odds with reality. The Y/R wire comes from the back of the speedo and goes to the connection farther down the road. In the wiring diagram, the Y/R wire is shown going to the first wiring harness, inches away from the speedo. But it does not, is a single solo wire that goes to a harness over a foot away. From there, it goes to the black box that contains the switch that you press to turn off the oxy. sensor lights when it comes on. (Time to replace the oxy sensor). Not like the wiring diagram which shows it going to the cigarette lighter and fibre optic bulb. The black box has Germany on it, so it is part of the Bosch fuel injection system.

Mine is an 80 so there may be a change from yours

[ga.spyder]

Pope, mine is the same as your 80.That is what I didnt understand,when I trace the wire it doesnt go to the lighter but to the box you mentioned.Should I just leave it alone,and forget swapping in the 140 speedo?I dont know if you have the speedo out,but that yellow/ red isnt on a connector but is hard wired into the 82 speedo. There is no provision for it at all on the older unit.Since it came off a carbed car maybe it is f.i. related
Craig

[kmead]

You can cut the wire with impunity. It only sends a signal to the box to then turn on a light to remind you to change your O2 sensor. If you are to cut it, leave some near the old speedo so if you ever want to go back you can.

So what are you going to do about the mileage discrepancy of the original and the different odometer?

[ga.spyder]

Thanks for the info on the wire!I was afraid to cut it w/o a verification on its function.We took this speedo out of the LeMons car we are building.My car has 74000+ and this speedo shows 71580.Not much difference!I will record the difference in my car ''logbook'',in case I ever sell it.Thanks again
Craig

[pope]

This is what I think, but cannot prove it.
The oxygen sensor console light comes on at a predetermined amount of miles to tell you to change it. When you hit the reset button in the black box, it causes the reset and waits to the next amount of miles in the speedo to pass. I think the Y/R wire sends a constant signal to the box and allows the box to start counting again upon reset.

You might have to put one of those clear oil change stickers in the upper corner of the windshield to know when the 30,000 miles has expired.

If you ask me, I think this is more than a good guess. I say go for the change. You can always switch back to a measly 85 MPH!

[rlux4]

Ain't it nice to have Pope around! I agree with everything he's saying, not that it matters.
I can see why you'd want to change the speedo out Craig, it's kind of embarrassing to have only 85 mph as max on the dash. My 19 y.o. son kinda snickers about it.
And 30,000 miles should be an easy number to remember, just change out the O2 sensor every 5 years!
Ron

[ga.spyder]

Snipped the y/r wire,and put in the 140 speedo.The car feels faster,and I havent even backed out of the garage yet! As far as changing the O2 sensor,at my current annual mileage rate ,I have to remember to change it in 2034! Hell,I'll be 76 years old and lucky if I can remember to change my Depends!!! Thanks,guys
Craig

[rlux4]

I got my car 2-1/2 years ago and it had 85K on it. It rolled over to 100K on the way up to Oregon 09, so I'm averaging a little over 5,000 miles a year.Trying to catch up with Ace, I think.
I'm checking to see if I can get all my tools in the little trailer, and use it for work too!
Ron