1975 Instrument cluster changeover with Tach

[RPOZ11]

Need some help looking at wiring in the wiring harness for adding this cluster.

The gauge panel that Im going to use has the Tach & AMPS gauge in it.

How do I tell if the wiring harness that I have is correct for that AMPS system?

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My truck's prior owners mixed everything up and I am attempting to correct it all.

I have already replaced the front light & engine harness with a reproduction loom.

Ill try to post an image of the wiring harness that I have for the under dash / inside cab.

[RPOZ11]

[RPOZ11]

[RPOZ11]

[RPOZ11]

[RPOZ11]

Im never good at electrical.
Can you guys guide me thru this?

Is this diagram helpful?

[hatzie]

What year truck did the harness come from?
Did the donor harness come from a gauge equipped truck?

73-75 with optional gauges were wired for the ammeter.
76 and after had the volt meter.

[RPOZ11]

I am aware of the Amps and Volts being different.
With that, does this harness look correct?
I believe it came from a 73 - 75 truck.

I guess what I think I need to know to look for is what color is the wire to the amps gauge,
using the printed circuit and tracing it back to the bulkhead,
looking for the correct color wire and correct use within this harness to the gauge cluster.

[hatzie]

You posted no pictures of the instrument panel plug. This is where the ammeter circuits will be most noticeable. All of the 73-75 that had gauges had an ammeter...

If you really have a 73-75 gauge harness then you should be set.
If it's a 73-78 warning light harness or a 76-78 gauge harness you'll need a different harness or different cluster... OR you'll need to modify the harness you have.

I scanned PDFs of all the Original GM wiring diagrams for the 67-91 10-30 CK & RV trucks and some other series. They are linked in my signature.
You can usually eBay paper originals that include the G & P chassis wiring diagrams as well as the 40-90 series trucks for less than $20.

That being said... In 73-75 the ammeter is circuits 105 & 106 Black and Black/White from the bulkhead plug to the instrument cluster plug. In the engine compartment both leads are fused inline with a 4A AGC fuse. Circuit 105 goes to the starter battery lug and circuit 106 goes to the junction stud on the firewall. DO NOT TAKE MY WORD FOR THIS. Look at the wiring diagrams yourself.

The old 16awg AGC fuse holders can be replaced with a Bussman 16awg HHF sealed ATC fuse holder if they are beyond repair.

[hatzie]

The 73-75 tachs have a, well deserved, bad reputation for failure. If your tach isn't tested it may not be working. The early tachs have coated boards, similar to potting, so board repair isn't really an option.

[RPOZ11]

Originally Posted by hatzie

You posted no pictures of the instrument panel plug. This is where the ammeter circuits will be most noticeable. All of the 73-75 that had gauges had an ammeter...

That being said... In 73-75 the ammeter is circuits 105 & 106 Black and Black/White from the bulkhead plug to the instrument cluster plug. In the engine compartment both leads are fused inline with a 4A AGC fuse. Circuit 105 goes to the starter battery lug and circuit 106 goes to the junction stud on the firewall. DO NOT TAKE MY WORD FOR THIS. Look at the wiring diagrams yourself.
.

OK, we located the black wire with the white stripe; its present.

On the black wire with NO white stripe, didn't initially see that one..
But
This is the ground wire for the wiring harness, correct?
Is it possible that the harness is grounded in a different location,
OR
Should be part of the plug in that connects to the dash cluster at the printed circuit?

I'll be at the truck today.
I'll take a pic of that instrument panel plug.

[ETKTRYD]

http://www.madelectrical.com/electri...p-gauges.shtml

[ETKTRYD]

Sorry link not working

[ETKTRYD]

Try this one.
www.madelectrical.com/electricaltech/amp-gauges.

[ETKTRYD]

One more time.....
http://www.madelectrical.com/electri...p-gauges.shtml

[RPOZ11]

Interesting article.
As I admit, electrical is not what I am good at.
What I did like from that article is that the load of the systems current now stands off of the starter stud.
Seems to me a good base for this rather than relying on weaker points.

As I am not a Dodge fan, yet looking at & reading that article, I assume that Dodge did not use a printed circuit?
My 75 uses a printed circuit with the gauge panel bulkhead connecting the harness to it.

[hatzie]

Download the 1975 GM wiring manual PDF from my signature... These are GM Factory wiring manuals not the Haynes and Chilton one-size-fits-all diagrams.
You'll find several answers to your questions in the wiring diagrams.
If you need to print the pages you'll need access to a wide format banner printer... At Fedex Office?? Printed banner pages are usually around $7 each so if you print more than one you'll be closing in on the cost of an original manual... far better off to snag an eBay copy of the manual then as they are usually around $20.

[RPOZ11]

Traced everything from the gauge thru the printed circuit, thru the bulkhead connector to the dash cluster;
Everything seems to match up correctly.
I guess that I am fortunate to have it all match.

Here's what I have...

[RPOZ11]

73-75 Tach Dash Cluster with AMPS

[rfmaster]

IRC when I installed my Tach cluster the tach board uses its own independent +12 volt supply harness. This small harness plugs into the back of it - one wire goes to Distributor Tach terminal.



//RF