How-To: 88-91 speedometer calibration 25085515 91' tach upgrade

[tommie]

this was a thread i made to swap a tach from a 91 into a 90 truck... so if that's what your doing and its the correct tach (v6 or v8) for your truck... then it should work...all of the info is in this thread....

[johnbrown]

8. Open the truck’s inst. panel plug...
Using the white pin, move the following wires.
Move B15 to B11,
Move A10 to A9,
Move A11 to A10.
Install the wire and pin assy. previously removed from the programmer plug into B15.
was going great but dont have programmer plug and local junk yard wants $55.00 for the plug with wiring trying to find just a wiring pin
thanks for your help

[jar head]

How do you change a v-8 tach to make it work in a v-6? I see the circuit that is marked 6 cyl and 8 cyl mine was soldered with the jumper in 8 cyl moved it to 6 cyl but it doesnt seem to read correctly . I s there something else I still need to change ?

[ChevyTech]

Originally Posted by jar head

How do you change a v-8 tach to make it work in a v-6? I see the circuit that is marked 6 cyl and 8 cyl mine was soldered with the jumper in 8 cyl moved it to 6 cyl but it doesnt seem to read correctly . I s there something else I still need to change ?

There is a different capacitor on the circuit board.
There is a good explanation in this link for a 92 to 94 style instrument panel.
This is on their old server so I don't know if a search would ever find it.
http://www.chevytalk.org/threads/sho...rue#Post722625

Welcome to the board!

[Aleks2505]

I know this is a very old post but hoping someone can help me out. I have got a hold of a 91 instrument cluster (the rare one) which has the identical plug at the back as my 88. From all I have read, this should be just a straight plug and play swap. However, when I plug this one in on mine, only the seatbelt light works and the right turn signal. The left turn signal also works, but the light stays on all the time in off position. Nothing else works. Just wondering if anyone knows how to test these things..if something is blown, I am sure I can get replacement capacitors for these things for pennies and solder them in. Visually, I don't see anything wrong with it, and I took it completely appart..no burnt chips on the board or buldging capacitors that I can see..anything else I should look for or that I need to do?

[JohnO356]

I can scan you the diagram/instructions around 1:00 PM Eastern time if you send me your email. You have to move a few wires.

[Aleks2505]

sure.
send it to maxzed88@gmail.com please and thank you.

[Aleks2505]

Oh man, I think I know what you are talking about now. I just realized that the info is in this very post, on another link. I think this is what you were referring to..ist it??:


7. Disassemble the programmer plug
Remove the white plastic teeth that lock the pins into the plug housing. Push one white pin into the plug from the other side (cluster side) to unlock and remove one wire and connector pin.

8. Open the truck’s inst. panel plug...
Using the white pin, move the following wires.
Move B15 to B11,
Move A10 to A9,
Move A11 to A10.
Install the wire and pin assy. previously removed from the programmer plug into B15.
Route a long wire through the firewall to the coil for tach sense pick-up. Hook this wire to the one you added to pin B15. Try going through the grommet for the cruise control harness.
The black slit corrugated wire wrap is now available at Radio Shack to make the added wire look factory installed.

9. The plug is numbered 1-17. Face the plug with the female ends facing you and the round alignment pins to the top and B1 will be on the left of the plug.




10. Hook the wire at the coil to the unused terminal next to the pink wire.

[JohnO356]

That's it

[Aleks2505]

Thanks JohnO356.
As soon as you said that I had to move some wires around, I remembered reading about it, but I though it had something to do with the callibration, and not the actual cluster. Thanks, you pointed me in the right direction.

[JohnO356]

Speaking of calibration, I hope your new cluster came out of a truck with the same engine and gear ratios. Those calibration kits are probably impossible to find now.

[Aleks2505]

Yes, you are correct, but there is ehough info out there to do it without that kit I believe. In any case, switched the wires last night, and the cluster woke right up. Now the only thing left to do is put some LED's in it, and run a tach wire, so my tach will work. Very pleased with it. Driving home last night, seemed like the speedo was very close. I am going to plug in my GPS today and take it for a run. My GPS tells me the speed almost dead accurate I find, as I used it in the truck before, so I will be able to gauge by it. If the speedo is off, I can always use the GPS for now. Just happy to get rid of those ugly moone gauges..they were awful.

[JohnO356]

There are several posts on fullsizechevy.com that may help with calibration if you"re way off.

[dragginmetal]

Tommie.
Im getting ready to do this mod but i have a question. On the 614street.com, the chart is different from the chart in the mag (page5). Im using .747559.
You said you had to do it more than once using the 614streets chart, so i was think of using the mag. one. Which chart do u think i should use?

614streets



Mag articular page 5

[ChevyTech]

Originally Posted by dragginmetal

Tommie.
Im getting ready to do this mod but i have a question. On the 614street.com, the chart is different from the chart in the mag (page5). Im using .747559.
You said you had to do it more than once using the 614streets chart, so i was think of using the mag. one. Which chart do u think i should use?

614streets
Attachment 1121437

Attachment 1121438
Mag articular page 5

I went and looked it up in a GM manual, and it shows the bottom chart selection you showed from (mag article page 5) is correct.

I show that the 614 streets information is wrong. As I have said before, there are several errors at that site.

[dragginmetal]

OK, Thanks. I'll give it a try and post what i find out.

[tommie]

thanks for the help chevytech.... the truck i did this on has been gone for a while now.... been fixing problems on the 97' now

[ChevyTech]

Originally Posted by tommie

thanks for the help chevytech.... the truck i did this on has been gone for a while now.... been fixing problems on the 97' now

You're welcome Tommie.

Thank you for taking the time to do a write up on this topic.

I have General motors handouts from when these trucks were new, that have information not found in service manuals, and I jump in when I see a question I can help with.

[pjmoreland]

Thanks so much, tommie, for posting this info! I just completed a conversion to a '91 tach dash on my '89 K1500. I ended up tweaking the calibration settings as well to improve the accuracy of the speedometer. I ran the tach signal wire through the firewall bulkhead connector on the driver side, and described it in this thread:

http://67-72chevytrucks.com/vboard/s...d.php?t=841923

Also, I re-pinned the gauge cluster connector without cutting the dash. I slipped the connector out of the gray housing first and left the gray housing back behind the dash. There is a wire retainer tray snapped to the back of the dash that I detached to make it possible to slide the gray housing farther to the right.

[Just call me Sean]

I didn't find any calibration charts that were correct. I had to mess with mine until the speedometer was correct. My trucks and van have the DRAC/VSSB though and I did the dip switches.