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#1 |
Post Whore
![]() Join Date: Aug 2014
Location: Sacramento, CA
Posts: 10,827
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Confused about re-pinning 74 Gauge Cluster Connections to a 78
putting in a 1978 gauge cluster with a tachometer into my 1974 GMC 1/2 ton that had gauges but had no tachometer
found the ORIGNINAL CLUSTER CONNECTIONS chart (thank you HATZIE) but am confused about repinning two things specifically IGNITION - on my '74 two pink wires go to pin #5 and #12, on the new '78 cluster somehow three pink wires need to go to #4, #6, and #12 however... RH TURN - on my '74 a Dk Blue wire goes to pin #11 but on the new '78 cluster somehow it also needs to go to pin #12 so there is a conflict on pin #12, who wins, the turn signal or the ignition? LOL |
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#2 |
Registered User
Join Date: Feb 2015
Location: Santa Rosa, Ca.
Posts: 539
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
Might be a dumb question but did you try tracing out the printed circuit for pin 12?
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1977 Chevrolet C/10 Silverado. Step-Side, Factory 454, TH400, 3.73 Posi 12 Bolt. 1975 Chevrolet El Camino. 350, TH400, 3.08 Posi 10 Bolt. |
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#3 |
Moderator
![]() Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,950
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
No conflict at all. You need to remove terminals and repin the cluster plug to match your new gauge cluster. This is why you can't just plug her in and go. The Ammeter wiring could make a nice crispy mess of the 78 printed circuit too.
1978 IGN circuit #39 is on terminals 4, 6, & 16 only. You'll need to find an extra terminal with a 12" chunk of wire attached as a pigtail. I'd suggest one of the two ammeter wires you'll be removing as you will not be using them for anything else. 1978 LH turn circuit #14 is on terminal 11. This is the only thing on that terminal. 1978 RH turn circuit #15 is on terminal 12. This is the only thing on that terminal. In the 1974 cab... Be very careful to remove and completely isolate the white and black ammeter wires found in terminals 2&3. Be careful to leave enough wire at the Instrument panel plug that you can use both terminals, if needed, for extra IGN, GND etc wires. Remove both glass Ammeter fuses in the engine compartment and replace with blown fuses. The ammeter is on circuits 105 & 106 in the GM wiring diagrams. The 106 fuse will be close to the junction block I'm not sure where the 105 fuse is. Instrument panel swap terminal guide from the 73-87 electrical FAQ. ![]() Year specific GM wiring diagrams are in the RTFM link below. Download both 1974 & 1978 GM wiring diagrams. Note: The cluster plug is shown in the GM wiring diagrams from the wire entry side not the terminal side... The terminal guide page from the FAQ is the opposite... Just to be confusing I guess. ![]()
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1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. Last edited by hatzie; 05-19-2015 at 04:26 PM. |
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#4 | |
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
Quote:
Here's how you would read it BLUE light - Hi beam - use Pin #1 and Pin #10 for ground YELLOW lights - cluster lights - use Pin #2 and Pin #10 for ground GREEN lights - turn signals - use Pin # 11 for left turn signal and Pin # 10 for ground - use Pin # 12 for right turn signal and Pin #10 for ground ORANGE lights - 4 Wheel Lock & Choke Lights - use Pins #14 and #16 for 4 Wheel Lock - use Pins #15 and #16 for Choke (* Pin #16 may just be a ground) RED lights - Belts and Brake Lights - use Pin #13 for Belts light and Pin #10 for ground - use Pins #17 and #16 for Brake light (* Pin #16 may just be a ground) done, nice and easy and in English and there aint nothing on there for IGNITION (Pins # 4, 6, 12) Pin #4 goes to the Volt Meter Pin #6 goes to Oil Pressure / Water Temp / Fuel (may just be a ground) Pin #12 goes to Right Turn Signal as a matter of fact I recall driving my truck with the entire gauge cluster unplugged and sitting on the work bench in my garage so as far as I'm concerned it has no ignition intelligence at all, but I'm learning so open to ideas Last edited by Gregski; 05-17-2015 at 11:43 AM. |
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#5 |
Post Whore
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
Thanks HATZIE you're giving us a lot of info so I want to break it up and go point by point.
The diagram I found shows it being on 4, 6 and 12, see the last column below |
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#6 |
Moderator
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Location: Wentworth, NH
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
I think the author of that sheet dropped the ball.
Position 12 is definitely the turn signal and 16 is definitely ignition power in 1978. Apparently the brake, choke, & 4x4 lamps use a switched ground.
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1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
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#7 | ||||
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
Quote:
Quote:
Quote:
The way you resolve the difference between my JPG showing the terminal side of the plug and the GM wiring diagrams showing the wire entry side of the plug is to find terminal 1. GM conveniently kept the High Beam Indicator wire on terminal 1 for all of the trucks that used the Delphi 8900371 eighteen terminal plug. The high beam lamp is circuit #11. Quote:
I clipped the pertinent section from the 1974 & 1978 wiring diagrams. 1974 doesn't have a circuit # legend but the 1978 circuit #s are the same with the exception of the ammeter wires #105 & #106 that are not present in 1978. 1974 Gauges 1978 Gauges
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1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. Last edited by hatzie; 05-18-2015 at 09:32 PM. |
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#8 |
Senior Member
![]() Join Date: Jun 2009
Location: Phoenix AZ
Posts: 4,564
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
Very nice info everyone! Wiring makes me go cross eyed! I just never can seem to wrap my head around it! I have the same problems with home electronics. Mechanical stuff is no problem for me though.
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AZPartsLocators on Instagram 1972 Cheyenne Super Short Bed big block "Blackie" 1977 Crew Cab GMC Short bed with 4BT Intercooled Cummins Diesel and a 4L80e "The Junkyard Dog" 1985 Crew Cab Chevy dually with 5.9 Cummins "The Big Dog" This is what my dad liked to be called by the grandkids before he passed so it seems fitting for his old truck. |
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#9 | |
Post Whore
![]() Join Date: Aug 2014
Location: Sacramento, CA
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
Quote:
Pin #2 is gray wire for cluster lights. Can I just remove that entire black and white wire with the fuse in it that runs from the small black two prong junction box on the firewall to the bulkhead connector on the firewall on the driver side? |
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#10 | |
Moderator
![]() Join Date: Oct 2008
Location: Wentworth, NH
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Re: Confused about re-pinning 74 Gauge Cluster Connections to a 78
Quote:
Removing the whole wire works too... That's the black with white tracer wire circuit 106. The black wire for Circuit 105 goes from the firewall plug, right next to 106, to one of the two fusible links on the 3/8" battery lug on the starter. Not sure where the inline 4A AGA glass fuse is in that wire.
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1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
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