Hello all, so I have an 87 GMC that has a 6.0 Swap and I am trying to install the 90-91 Suburban Speedo (Electric). I have RePinned the harness correctly and all the other gauges seem to be working properly except for the Speedo. Whenever possible I have tried to minimize the use or reusing of the Bulk head wiring (since I heard of stories of those wiring failures) such as Water Temp, Oil Pressure, Fuel and Speedo (VSS Signal) - all those wires have been reran directly to the gauge cluster location and all are working. A lil backstory I bought the truck almost a year ago with the LS Swap already done and the gauges also came with the sale but I am just getting to wiring it in - trying to get it working before the upcoming Power Tour. I called myself trying to update the cluster and I installed LED bulbs which ended up being an issue on some of the circuits because I guess it was not providing the correct resistance, so I reverted back to the 168 Halogen bulbs and that solved some of the other issues I was having but the Speedo issue has me stumped.

So I have it directly wired to the GRN/WHT wire of the LS Conversion harness (has Blue/Grn Connectors - if it matters) and here are some of the things the Speedo is doing. when I turn the truck on (and the truck in Park) after a few moments the needle jumps up to about 65-75 mph (Again while in Park). So its definitely receiving a signal but its not the "Right" signal. Also (with the truck up on Jackstands) I put the truck in Gear and the odometer is rotating as if the mileage is being counted but again the Speedo Needle is not doing anything. Then when I turn the truck off the Needle rests on the other side of the speedo at the 85MPH location.

Can anybody PLEASE provide some guidance - I am lost, I have been online researching and reading with no success and only have about 10 days before we hit the road for the Tour.
Thanks in advance for any and all help.

 

DAMN 58 views and no one has experienced this issue before???
Bump to the top!
8 days to go - Looks like I'll be doing the Power Tour with No Speedo.

 

tape phone to dash and download a speedo app
problem solved thank me later

 

ahahahah that was my PLAN B - but I was trying to get the gauges working correctly.

 

Recheck your cluster pinout. I posted a diagram on 67-72 forums a LONG time ago. I need to look it up myself for another swap. Don't think I have the link or pic saved.

 

Yes Sir!!! I have checked the pinout multiple times - should be pin 18. I’ve even unplugged the Plugs at the PCM and ran a Continuity Test to make sure I had the correct pin location/wire and it passed. So I’m lost.