75 k5 blazer. Installing a New Vintage gauge cluster. A few weeks ago before I got the gauges I started identifying all the wires at the main plug. I very clearly had two accessory power wires at pins 5 and 12 that worked just fine. fast-forward a few weeks when I went to start to install the gauges I no longer had accessory power from the very start. To clarify, I didn’t lose power after I started splicing into other wires, right when I sat down to start the project the accessory power was gone. I started doing everything else thinking I would figure out the accessory power at the very end, and that’s where I’m at now. Everything is completely hooked up ready to go, and I suppose I can get accessory power from somewhere else but it’s bothering me that all the other wires to that main factory plug work except for that. I checked all the fuses and obvious stuff, but nothing seems to have changed or is blown. Any ideas?
CK5
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Randomly no acc power to gauge cluster
- Thread starter Damufuer
- Start date
I do not know which pins 5 and 12 are. Do they have power with ignition on?
The main factory plug is labeled. Pin 5 looks like the main power source to the cluster because there are two wires going into it. Idk what 12 was but it did have power just a few weeks ago.
To answer your other question they are both completely dead now, no power at any time.
To answer your other question they are both completely dead now, no power at any time.
What plug are these in?
rampage
3/4 ton status
Out of curiosity, how did you make the splices?
Is there an easy way to check the voltage on the original acc wires before the splice, either where you spliced or by tracing the wires back to an accessible point?
Or remove the new wires you spliced on and see if you get power back to acc.
EDIT: scratch that. If I’m understanding correctly then you lost power before you spliced. Obviously you jiggled some wires loose (either positive or ground) or shorted something out while you were checking for voltage, too much of a coincidence. How are you checking voltage (meter/probe pen/test light)?
Is there an easy way to check the voltage on the original acc wires before the splice, either where you spliced or by tracing the wires back to an accessible point?
Or remove the new wires you spliced on and see if you get power back to acc.
EDIT: scratch that. If I’m understanding correctly then you lost power before you spliced. Obviously you jiggled some wires loose (either positive or ground) or shorted something out while you were checking for voltage, too much of a coincidence. How are you checking voltage (meter/probe pen/test light)?
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rampage
3/4 ton status
Not sure if you have access to the ‘Technical Service Manuals’ section on this site, but here’s a link for your ‘75. Download the 1.6MB pdf file and you’ll have the wiring diagrams.
https://ck5.com/forums/threads/1975-gm-technical-manuals.348566/
If you don’t have access, then here are the important parts. The first pic is the connector you’re referring to I believe. It shows that pin 5 has the two wires going into it (labeled 20P-39A and 20P-39B). 20P-39B is just a wire that goes from pin 5 to pin 12.
In the second pic you can see that wire 20P-39A goes directly to the fuse panel. The left side of the pic is the back side of the fuse panel and the right side of the pic is the front side with the fuses. Check the fuse with a meter to make sure it has continuity or zero resistance. Also, just to entertain me, can you verify you have 12V on your battery and at the fuse panel to make sure it didn’t die from the last time you were messing with it. Sounds stupid and simple but need to cover those bases.
https://ck5.com/forums/threads/1975-gm-technical-manuals.348566/
If you don’t have access, then here are the important parts. The first pic is the connector you’re referring to I believe. It shows that pin 5 has the two wires going into it (labeled 20P-39A and 20P-39B). 20P-39B is just a wire that goes from pin 5 to pin 12.
In the second pic you can see that wire 20P-39A goes directly to the fuse panel. The left side of the pic is the back side of the fuse panel and the right side of the pic is the front side with the fuses. Check the fuse with a meter to make sure it has continuity or zero resistance. Also, just to entertain me, can you verify you have 12V on your battery and at the fuse panel to make sure it didn’t die from the last time you were messing with it. Sounds stupid and simple but need to cover those bases.
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Thanks so much for your help. I traced the wire back to the rear of the fuel panel and something was off with the connection, where when I messed with it I got power back to the main connector. I’m not really sure how anything got dislodged back there, as I was never back there, but happy it’s fixed now. Thanks again!
rampage
3/4 ton status
Thanks for the update. Glad it’s fixed. 
