Wiring up a 1979(?) cluster in a 1990 K5.

[82355]

My 1990 K5 has a doubler, so I no longer have a speedometer output on my transfer case. I bought a used 1979(?) gauge cluster with a factory tach for $20. I am not sure on the age of the used cluster, but it has all electronic gauges, and the older font. Anyway, I chased all the wires and the printed circuit, and changed all the pins around. It mostly works, I just have a few questions.

The fuel gauge no longer works. There were two wires running to the gauge in the '79 cluster, and only one wire for the '90 cluster. I hooked just the one wire up, and it just pegs the fuel gauge. What is the other wire I need to hook up? Just a ground?

My Temp gauge registers, but is not accurate. It barely moves off the low peg. Does it use a different sending unit between the years? There is no reason I can't just pull the Temp gauge out of the '90 cluster, and install it in the '79 cluster, is there?

I was also thinking of swapping the oil pressure and Volt Meter gauges between the two clusters.

Anyone with experience here, feel free to chime in please.

Martin

 

[tRustyK5]

I did a mix and match cluster in my '90 using a '78 tach dash. I spent a fair bit of time studying the printed circuit on the backside, and tracing each path back to the wiring that plugs into the cluster...then mapping what wire did what. I found each gauge has power, ground and sender. I traced what I needed to and wired my fuel gauge independently of the printed circuit using bullet connectors to the gauge pins.

I did mine backwards to what you did, still having a VSS speedo but adding the tach and small fuel gauge to the '90 cluster.

 

[nvrenuf]

I soooo wanted to cross breed an '81 tach cluster into my '91 K5 but I'm just too A.D.D. to do it. I traced and traced until I was blue in the face and gave up. I envy you guys, that's really trick stuff to make work together.

 

[p0ps45]

I soooo wanted to cross breed an '81 tach cluster into my '91 K5 but I'm just too A.D.D. to do it. I traced and traced until I was blue in the face and gave up. I envy you guys, that's really trick stuff to make work together.

I did my 91 K5 with the stuff you sent me Tach just spun circles so I had to get another

 

[82355]

My tach moves smoothly, I think it reads a bit high though. They are not adjustable, are they?

Martin

 

[p0ps45]

Mine was the same way. I just took the pointer off and moved it to the correct reading @ idle. Seems to be accurate now.

 

[tRustyK5]

I soooo wanted to cross breed an '81 tach cluster into my '91 K5 but I'm just too A.D.D. to do it. I traced and traced until I was blue in the face and gave up. I envy you guys, that's really trick stuff to make work together.

The PC made my eyes cross for a while, until I finally realized 80% of what I was tracing was a redundant, multi-path ground. Once I ticked each ground path with a sharpie marker the rest became a lot easier to figure out. ground goes back to the plug in about 8 or 9 different places...

The next tricky part is looking at the back of the cluster and comparing it to the plug of wires that push into it for wire tracing/mapping. You have to keep reminding yourself left side on the cluster is right side of the plug and vicy-versy.

Other than that, it's straight forward other than being a bit tedious.

Here is my cluster working...

 

[82355]

Yeah, my 1990 cluster had three unused pins, and only one ground. The 1979(?) cluster had three different grounds, I just spliced them together. I assume I missed a ground for the fuel gauge?

Martin

 

[p0ps45]

Yep sounds like you missed one. I just hard wired the gas gauge to the old connection locations on the circuit board.

 

[82355]

There was only one wire running to the large gas gauge on the '90 cluster. The printed circuit on the '79(?) cluster had to 'wires' running to it. Not sure what to wire to it?

Martin

 

[p0ps45]

I just soldered wires to the original gauge connections (circled in pic) and connected to the new gauge. I don't have pics of the finished one & of course I'm not near the truck today. The easiest way to do this is to swap the tach and fuel gauge to the 90 cluster. You have to trim the plastic for the fuel gauge location but you are also not dealing with re-pinning the cluster connector.

 

[82355]

I have no VSS. I have already repinned the connector. I just have to figure out what I need to add to the fuel gauge to get it to work. I think I am going to tear it apart, and figure it out, and swap in my newe volt, temp, and oil gauges.

Martin

 

[82355]

Tore into it today and figured out my problem. Had to add an additional ground for the Fuel gauge. The 1990 used one ground. The 1978 cluster (I believe it's a 1978 now, I just bought another tach cluster from a 1979 and it says UNLEADED FUEL ONLY under the Fuel gauge) has multiple grounds. The 1990 cluster has a better laid out ribbon, and it is also labeled better. Anyway if anyone is curious, here is a list of what pins are what wires after I wired it up in place of a 1990.

Old Cluster with Tachometer (1978 or 1979??? No mechanical gauges)

Pin # - Fuction - Wire Color from 1990 K5 Blazer

1 - High Beam Indicator - Light Green/No Stripe
2 - 12 Volt + Controlled By Headlamp Switch - Light Gray/No Stripe
3 - Ground - Black
4 - 12 Volt + Keyed To Ignition Switch - Pink/Black Stripe
5 - Oil Pressure Gauge From Sender - Light Brown/No Stripe
6 - 12 Volt + Keyed For Fuel Gauge - Pink/Black Stripe
7 - Fuel Gauge From Sender - Pink/No Stripe
8 - Ground (for Fuel Guage) - Yellow (I cut out the seat belt warning lamp for this, tied into the Black ground wire)
9 - Temperature Gauge From Sender - Turquoise/No Stripe

10 - Ground - Light Blue/Black Stripe (tied into Black ground wire)
11 - Left Turn Signal Indicator - Light Blue/No Stripe
12 - Right Turn Signal Indicator - Dark Blue/No Stripe
13 - Seat Belt Reminder Lamp - Yellow/No Stripe (I ended up cutting this out and using the wire/pin for my fuel gauge ground)
14 - 4x4 Indicator (there was a separate wire not part of the 18 pin connector, I have a doubler, so I did not use this)
15 - Choke Indicator - Dark Brown/White Stripe (Is now my Service Engine Soon lamp)
16 - Ground - Dark Brown (tied into Black ground wire)
17 - Park Brake/Unequal Brake Pressure Indicator - Light Brown/White Stripe
18 - Not Used

Here is how the 1990 K5 was originally wired up with the factory electronic speedometer:

Pin # - Function - Wire Color

1 - High Beam Indicator - Light Green/No Stripe
2 - Ground - Black
3 - Oil Pressure Gauge From Sender - Light Brown/No Stripe
4 - 12 Volt + Keyed From Ignition - Pink/Black Stripe
5 - Low Voltage Warning Lamp - Dark Brown/No Stripe
6 - Not Used
7 - Not Used
8 - Coolant Temperature Gauge From Sender - Turquoise/No Stripe
9 - 12 Volt + Controlled By Headlight Switch - Light Gray/No Stripe

10 - Left Turn Signal Indicator - Light Blue/No Stripe
11 - Right Turn Signal Indicator - Dark Blue/No Stripe
12 - 4x4 Indicator Lamp - Separate wire from 18 Pin Connector
13 - Seat Belt Warning Lamp - Yellow/No Stripe
14 - Fuel Gauge From Sender - Pink/No Stripe
15 - Park Brake/Unequal Pressure Warning Lamp - Light Brown/White Stripe
16 - SES (Service Engine Soon) Lamp - Dark Brown/White Stripe
17 - 12 Volt + Keyed From Ignition Switch - Pink/Black Stripe
18 - Speedometer From Sender - Light Blue/Black Stripe

Martin

 

[82355]

Hope someone can find that to be useful information. I would have loved to have had it before I did the swap. I spent a lot of time chasing wires and ribbons.

Martin

 

[tRustyK5]

Nice job, I'm sure it'll be useful for quite a few people. I should have done what you did when I did mine, but at the time I was working on it it didn't really occur to me. After it was done it crossed my mind...

 

[thundertiger25]

Helpful!

Hope someone can find that to be useful information. I would have loved to have had it before I did the swap. I spent a lot of time chasing wires and ribbons.

Martin

Thanks for your posting up that info it was exactly what I was looking for! I'm currently looking through the factory wiring diagram and tracing wires from back of the cluster to the harness. This helps confirm most of what I have, Thanks alot!

 

[82355]

No problem, I am glad it could be of some help to someone else.

Martin

 

[Moosehunt]

Since you guys Are working on a 90' Cluster , how hard is it to replace the instrument lights. I can't read my speedo at night!
The reason I Ask is= I thought I read here awhile back that the instrument lights are not replaceable on 90-91, that you had to replace the whole cluster?
true or not?

thanks in advance,
Dan

 

[p0ps45]

You don't have to replace the whole cluster. The bulbs and holders are 1 piece, so you have buy the whole assembly, not individual bulbs.

 

[Moosehunt]

whew! Thanks-a-bunch pOps45 I really appreciate the reply!