Speedo ?

[94.Sierra]

How is the speedo set up on these trucks. Is it the plug on the tailshaft of the transmission? I swapped from a 4l60e to a 700r4 and I left the trans harness unplugged(used a lockup harness instead) and now my speedometer doesn't work.

 

[Devs93]

-what year?

guessing 94 from your name yes there is a sensor on the tailshaft that ties into drac the drac ties into the ecm speedo cruise and abs

 

[94.Sierra]

truck is a 94 but the 700r4 i'm using is out of a 91. Tailshaft are exactly the same and have the same plug.

 

[Devs93]

88/91s had a diff speedo setup they used moonie gauges and the wires that came off the sensor went straight to the speedo. umm Ive seen info on this before just gotta remember were. Since the speedo isnt working is it not shifting out of first either?

 

[94.Sierra]

Thats weird cause I just went out and plugged the tailshaft plug in and it seemed to fit fine, I just haven't taken it on the road again to see if speedo is working. It shifts out of first fine and I have a vaccuum lockup harness to control 4th gear lockup. I'll have to go for a drive to see if anything changed lol

 

[Devs93]

yea they 4l60 e and 700r4 use the same sensor alls it is is a magent that reads the spins. if you wanna see something real trippy chase that wire down to were it plugs in the dash hook a voltmeter on there and drive down the rd it will read ac current instead of dc

 

[94.Sierra]

Oh I see, so definitely don't plug the 4l60e's plug into the 700r4 then? haha. I don't mind driving without the speedo was just wondering if it was as simple as plugging in the old trans harness

 

[Devs93]

yea just plug it in if it fits

 

[94.Sierra]

Okay. Off topic but another problem I have is my brake lights aren't working. I had this problem before and a guy on here told it was because I didn't have the trans lockup harness hooked up yet. So i hooked it up and my brake lights worked, but now they don't again any ideas on this?

 

[Devs93]

chevk your fuse if its bad it could also be the reason your speedo isnt working