Gauge cluster wiring

[sqtrk]

I recently purchased a 1986 c10 and some of the guages are not working. I'm still working on troubleshooting the cause. I pulled the instrument cluster out today to examine the circuit board. In doing so I found a strange ligh mount and wire. The wire was

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not attached to anything and has a strange connector. Would anyone know the purpose for this odd connection, what it does, and what the wire should connect to? Picure attached.

I realize this likely does not impact my gauges but wondered what this odd design is good for.

 

[Originalthor]

It goes to your ashtray for a light. Its fiber optical cable.

 

[John Nes]

It goes to your ashtray for a light. Its fiber optical cable.

Originalthor nailed it.
As for the gauges, if your fuel only reads 1/4 full but will still go down to E - gauge is busted. If fuel gauge needle goes was past full, check continuity of your wire from the sender to firewall.
If oil pressure is stuck at 15, it’s prob the gauge but double check with a mechanical gauge off the engine. If gauge is pegged, check continuity of the wire to the oil pressure sending unit (big ol brass can lookin thing) and check the cleanliness of the packard56 female terminal that’s at the end of the oil pressure sending unit wire.

Saved the best for last, temp gauge. Most the time, the female terminal has fallen off the sending unit (on the block between #1 + #3, landed on the manifold or headers, and melted into oblivion. Your gauge needle would be pointing to nearly 3 o’clock, and would climb as soon as you key on/have switched 12v power to cluster. This wire is prob the easiest to check of the gauge sender’s. However if your temp gauge isn’t showing the correct temp, (way hot/way cold) there’s a resistance issue. There’s a handful of sending units for 73-87’s for coolant temp that corresponds with that an era specific gauge’s ohm resistance values. If you’re unsure of the gauges being original or not, just Google the gauges and compare the font/colors/numbers vs C-H on the face.

I should mention that after checking wiring/connections/presence of sending units even being there, or measuring resistance levels, you should take note of the printed circuit board’s condition. It’s that celluloid and copper ribbon “sheet” that’s behind the cluster housing, if the contact points have become separated from the printed circuit board’s copper ribbon tracers, you’ll also have issues with gauges/dash lights working. PCB’s can be found new, all over the internet, if needed, just make sure you order the right one for your truck.

And for the hell of it, it’s never a bad idea to scuff any of the wiring’s terminals with some emery cloth before reconnecting for better contact.

 

[sqtrk]

Thanks for the quick replies, appreciated!

I had no idea the was a fiber optic cable!

 

[75gmck25]

Another useful product is DeOxit spray. If you can see two switch contacts that slide or spring against each other, or you have an exposed terminal and connector, there may be oxidation on the exposed metal and it may not make a good electrical connection. DeOxit is designed to remove the surface oxidation and make a better connection.

 

[cbsuguy1]

not to hi-jack the thread but where does the light end of that attach?

 

[Snoots]

There is a slot in the top of the ashtray drawer for that.

 

[Rick R]

I am looking for the fiber optic strip that illuminates the windshield wiper on a '73 C10. If anyone has one or a source for one, please let me know.
I am also going to be using a later model cluster with a tachometer. I am also using a voltmeter as opposed to the original ammeter. My question is should I get a PCB for a '76 that uses a voltmeter or rewire a '73 PCB?

 

[Mr Clean]

 

[75gmck25]

Rewiring for a voltmeter is very simple, so I wouldn’t bother switching PCBs. I found a short article on the internet that explained where to get power and ground from the existing wiring of the cluster, which is all you need for a voltmeter. Just do a Google search and you should be able to find the article.

For my ‘75 I bought a replacement voltmeter from LMC, and the only other items needed are short jumper wires and ring terminals.