1980 printed circuit w/tach

[Tony_W]

Hey guys, long time reader but just finally joined.

Have a 1980 c10 2wd. I installed a new harness from speedway.

I'm having trouble indentifying on the printed circuit the tabs for Ground/hot/signal.

Purchased a new wiring harness from speedway and so far so good. I purchased new back bezel from LMC that has the tach spot in place of the big old gas guage and I picked up a printed circuit from them also with tach. I picked up the speed guage and the small gas guage.

LMC has the small gas guage marked for signal/ground/hot but going from there I'm not confident. I don't want to toast anything so I have been looking for something that shows Hot/ground and signal. This factory blue wire or orange wire does not work for me since I'm using the speedway harness.

Anyone know of a layout pic of the printed circuit that I can see that shows all the guages and lights on a 1980 printed circuit with tach ground, hot, signal?

Appreciate any feed back, until then I'm stuck on my project.

[ray_mcavoy]

The pin-out for the 1978 through 1987 gauge clusters is:

pin #
1 = high beam indicator
2 = cluster illumination
3 = ground
4 = +12V feed (switched via ignition)
5 = oil gauge sending unit
6 = +12V feed (switched via ignition)
7 = fuel gauge sending unit (for small fuel gauge in lower left corner)
8 = ground
9 = temp gauge sending unit
10 = ground
11 = left turn signal indicator
12 = right turn signal indicator
13 = fasten seatbelt indicator
14 = unused/empty
15 = choke indicator light
16 = +12V feed (switched via ignition)
17 = brake warning light
18 = fuel gauge sending unit (for large gauge to right of speedometer)

The pins are numbered on the factory connector plug. But if you don't have that, pin #1 is located in the upper driver side corner of the cluster and they go #1 through #9 down that side of the connector. Then pin #10 is on the bottom driver side corner and they go #10 through #18 up that side of the connector.

The tachometer uses it's own stand-alone 3-wire harness that does not connect to the printed circuit. If you look closely at the plastic mounting plate on the back of the tach it should have markings next to the terminals for +12V, GND, and COIL.

[Tony_W]

Thanks Ray, big big help.

I still have my plug so easy peasy on numbers match up.

I'm doing all electric guages even on oil.

With this speedway harness I have the signal wires that will go in place, then I make my own grounds and 12 volt supply (the wires are in the kit). Looks to be I bounce the 12V and tie into the one wire in the kit, off thier directions.

Which number would be the voltmeter or amp meter?

[Tony_W]

Originally Posted by ray_mcavoy

The pin-out for the 1978 through 1987 gauge clusters is:

pin #
1 = high beam indicator
2 = cluster illumination
3 = ground
4 = +12V feed (switched via ignition)
5 = oil gauge sending unit
6 = +12V feed (switched via ignition)
7 = fuel gauge sending unit (for small fuel gauge in lower left corner)
8 = ground
9 = temp gauge sending unit
10 = ground
11 = left turn signal indicator
12 = right turn signal indicator
13 = fasten seatbelt indicator
14 = unused/empty
15 = choke indicator light
16 = +12V feed (switched via ignition)
17 = brake warning light
18 = fuel gauge sending unit (for large gauge to right of speedometer)

The pins are numbered on the factory connector plug. But if you don't have that, pin #1 is located in the upper driver side corner of the cluster and they go #1 through #9 down that side of the connector. Then pin #10 is on the bottom driver side corner and they go #10 through #18 up that side of the connector.

The tachometer uses it's own stand-alone 3-wire harness that does not connect to the printed circuit. If you look closely at the plastic mounting plate on the back of the tach it should have markings next to the terminals for +12V, GND, and COIL.

Ray, do you know which number is the Alternator light?

Some call it the idiot light, but anyways you get what I'm asking, when ya turn on the key and the Alt. Light comes on.

[ray_mcavoy]

Originally Posted by Tony_W

Ray, do you know which number is the Alternator light?

Some call it the idiot light, but anyways you get what I'm asking, when ya turn on the key and the Alt. Light comes on.

Hi Tony,

The factory gauge clusters do not have an alternator light. Those were only used in the base clusters that simply had a speedometer, fuel gauge, and warning lights for everything else. Those clusters have a different pin-out and use #6 for the alternator/battery light ... whereas #6 is a +12V feed on the 78+ gauge clusters.

Many alternators have the alternator field excitation circuit wired through the alternator light. But in trucks with the factory gauge cluster (that didn't have that light), GM included a special resistance wire (about 10Ω) in the dash harness. So depending on what you are using for an alternator, you might have to add in a resistor. Or if you want, hook up your own alternator light independent of the gauge cluster wiring.

[Tony_W]

Thanks Ray.

I've got a drain on the battery 13.28 volts. But, the Delco 3 wire alternator is good, starter is good, grounds are good. Everything works great and all lights are bright evenly.

I don't have a radio yet, no A/C. My interior light is only on the headlight switch. Basically the truck has a heater and wipers.

If I have the Alternator hooked up, which is power to the back from/thru starter and the wire thru fuse box going to plug number 1of the Alt that tells the Alt to turn on., and I have plug number 2 jumped to the back of the main power of the alternator which I believe tells the Alt to charge or not to charge, she drains the battery.

But if I unplug number 1 and leave number 2 plugged up, no drain, if I unplug number 2 and plug number 1 back up, still no drain.

This is why I asked about the idiot/dummy light.

Should there be a diode on one of those wires on plug 1 or 2 by chance?

[gmachinz]

The ground goes to dash/chassis, coil goes to HEI but also requires a tach filter (which I stock) and the +12V goes to an IGN source at fusebox. The LMC tach harness aren't correct for HEI trucks-which is why I offer the correct HEI tach harness if you need one.

[Tony_W]

Originally Posted by gmachinz

The ground goes to dash/chassis, coil goes to HEI but also requires a tach filter (which I stock) and the +12V goes to an IGN source at fusebox. The LMC tach harness aren't correct for HEI trucks-which is why I offer the correct HEI tach harness if you need one.

Thanks I will keep this in mind.

I still need to find out Which number would be the voltmeter or amp meter?

[ray_mcavoy]

The voltmeter in 1976 & up clusters uses the +12V ignition feed on pin #4 and the ground on pin #3.

The ammeter in 1973 - 1975 clusters also uses pins #3 & #4 but the wiring is different. The ammeter connects to one of the charging system wires under the hood that serves as a shunt. Neither side of the ammeter is grounded. And connecting an ammeter between power & ground would create a short circuit that can melt wires and/or traces on the printed circuit. That is why you see folks post warnings not to plug a 73-75 ammeter cluster into a 76+ truck that is wired for a voltmeter.

[Tony_W]

Originally Posted by ray_mcavoy

The voltmeter in 1976 & up clusters uses the +12V ignition feed on pin #4 and the ground on pin #3.

The ammeter in 1973 - 1975 clusters also uses pins #3 & #4 but the wiring is different. The ammeter connects to one of the charging system wires under the hood that serves as a shunt. Neither side of the ammeter is grounded. And connecting an ammeter between power & ground would create a short circuit that can melt wires and/or traces on the printed circuit. That is why you see folks post warnings not to plug a 73-75 ammeter cluster into a 76+ truck that is wired for a voltmeter.

Thanks again ray, I might change my mind on the voltmeter and go clock.

[ray_mcavoy]

Okay, I see what you are dealing with now.

You mentioned #1 & #2 terminals so I assume you are using a 10SI or 12SI alternator, correct?

The #2 terminal is a voltage sensing terminal and can be hooked to a point that is live all the time so you're okay there.

The #1 terminal is the field excitation terminal (and also operates an alternator light in applications that use one). This terminal has to be hooked to a power source that is switched on & off via the ignition. I see you mentioned hooking this up to a wire from your fuse box ... have you checked to make sure that particular wire switches off with the ignition? Some wires in the fuse box stay live all the time.

The circuit to the SI alternator's #1 terminal should also include a resistor (10Ω minimum) to limit current through the alternator's diode trio and prevent backfeeding that could keep the engine from shutting off. Some folks add a diode to the #1 circuit to prevent backfeeding. But no matter what you use, this terminal still needs to be hooked to a source that is switched off via the ignition to prevent battery drain.

[Tony_W]

I believe it's the 10SI, will double check

ok, thanks.

No problems shutting off, so far everything is the way it's suppose to be.

I will have to check on the wire number 1 with a multi meter to see if it has power with key off.

[Tony_W]

The wire to number 1 shuts off when ignition is turned off.

Got a (dumb) question when the ignition is off should I still see 13+ volts at the back of the Alternator? Which is The power wire coming from the starter to the back of the Alternator.

Basically the key is off and I still show power on at this terminal.

[ray_mcavoy]

Power to the #1 wire turning off with the ignition is good so you can rule that out as the source of the battery drain.

Yes, the output stud of the alternator should be at battery voltage all the time. So should the #2 voltage sensing terminal. That is normal and should not drain the battery.

Have you had the alternator tested? And if so, what type of test(s) were done? A shorted / leaky diode in the alternator's bridge rectifier assembly can create a parasitic drain on the battery. And the alternator will still be able to generate power (although not to it's full rated output) with a bad diode.

[Tony_W]

I had the alternator checked last week with a supposedly reputable outfit dedicated to starters and Alternators.

He took it apart checked diodes and found nothing wrong, put it back together and test it and it passed he told me.

Now the only way I know how on parasitic drain (which I was recently taught) was use the multimeter direct current on 20 volts, unhook the ground off the battery.

Touch the negative(black) multimeter prong to the cable ground and then touch the positive(red) multimeter prong to the negative post of the battery with ignition off to see if I read any volts, which I do, I show the full amount of battery and it's 13.28.

This sound correct to you on how to check? The multimeter tool is all I have except a test light.

I just don't understand why it's showing a draw at 13.28 like the power is on all the time? I can't explain it to me in my head, nothings jumping out lol.

It's a sbc with just heat and windshield wiper motor, I even unplugged those lol, no change.

[ray_mcavoy]

Originally Posted by Tony_W

Now the only way I know how on parasitic drain (which I was recently taught) was use the multimeter direct current on 20 volts, unhook the ground off the battery.

Touch the negative(black) multimeter prong to the cable ground and then touch the positive(red) multimeter prong to the negative post of the battery with ignition off to see if I read any volts, which I do, I show the full amount of battery and it's 13.28.

This sound correct to you on how to check? The multimeter tool is all I have except a test light.

You're close. Except you want to set your multimeter to read DC current (Amps or Milliamps), not Volts.

[Ol Blue K20]

After reading through this thread. I can't run a tach cluster in my 89 V3500 with a tbi454?.

[Ol Blue K20]

Awesome Ray, I'll pull my cluster and compare side by side and go from there. Worse comes to worse I'll get the conversion and offer up the other cluster on the parts board. Thanks for sharing your knowledge and your help......

[Ol Blue K20]

Awesome Ray, I'll pull my cluster and compare side by side and go from there. Worse comes to worse I'll get the conversion and offer up the other cluster on the parts board. Thanks for sharing your knowledge and your help......