1972 Rally gauges w/120 speedo
 

72 Lemans sport conv 350-2

OK,
I want to change from warning light cluster to rally gauges on a 120-seatbelt warning car. I have the 120-gauge cluster and want to keep the seatbelt warning system operational. I've searched the forums and found a few different posts about which wires to switch but are conflicting. It seems a lot of the posts refer to guys switching from 120 warning clusters to 140 rally clusters. Has anybody done the switch and can tell me which wires to switch?

Bill, do you have a 1972 Pontiac Service manual?
This should be similar 2 wire swap deal as used to convert '68, 69-early '72 A-bodies from idiot light harness to Rally gauge harness.

I'll ck out my '72 Pontiac Service manual this weekend & post back.

Unfortunately I do not see the wire for the seat belt lamp. And looking at the Ames catalog shows 2 different circuit boards - the harness contact pads seem to be different too.


https://forums.maxperformanceinc.com...1&d=1779489160

No, unfortunately I let it go with the sale of my last 72. I have a wiring diagram but like what Scarebird's post shows it only covers the 69-early 72 wiring.

The legend of connector pads is wrong in the '72 service manual for rally gauges, think the gen light and fuel tank are the two wrong (reversed), been awhile. Use the schematic when switching pins on the connector, schematic is right.

Don't really know what I'm looking at. Can anybody decipher?
Found one post from 2003 that says:

Shift #1 to #12
Swap #6 and #5
Shift #3 to #2
Shift #2 to #1
Check extra tan 12, can put in slot nc..

Does this sound right?

Here is the printed circuit board cluster with seat belt diagrams. I haven't verified pinout though.

Is this the thread you've referred to?
https://forums.maxperformanceinc.com...d.php?t=426632

That's it...

Well, post #11 should tell you what to properly swap.
#3 gets the wire from #12. #5 and #6 get swapped. That looks like it.

I tried to post bigger pics of HFR's pics, but this site doesn't support bigger pics.

:mad:

These are from the service bulletin for the seat belt buzzer harness change.

See if they are clearer?

Rally Gauge pic

No Rally Gauge pic


:confused:

I'm gonna try it. I'll let everyone know if it works. Thanks everyone.

Lots of great info here, so thanks to all of those contributing.

I am at a stage of rebuilding from no gauges to gauges. I have the entire under dash harness out for repairs and am getting ready to do the entire dash before re-installing it. I also have the manuals plus a pdf copy on my computer.

Since the numbers in the '72 repair manual are designating the circuits, and the numbers on my connector (pics below) are not referenced, I want to make sure I match them up. If I take the wide connector location and just write down 1 - 12 next to the manual's 8 - 39 pic will it work?

Sorry for the confusion,
Ogre

Does this make it easier?

Just noticed both drawings show the same layout.
And looking at the gauges printed circuit board, your plug is showing correctly positioned wires.

Service manuals were usually printed in August prior to fall production. Since the 120 MPH / Seat Belt Warning instruments were used after Dec 31, 1971, the new modified harness would not be in the service manual.
A Service Bulletin was issued detailing the changes as shown in post #12

Thanks, HFR. That makes it clear.

Ogre

https://forums.maxperformanceinc.com...6&d=1780350142

Here you go

Well, tried all the different wire swaps and couldn’t get gauges to work. Bought a new harness from M&H for gauges. I’ll post results. Is the circled green wire the one that needs to be taken out so gauges don’t peg upon start up?