electrical - firewall->fuse box connection --- also paint question

[tard01]

so i got my continuity tester last night to work on my electrical problem.

issue:
front headlights dont turn on
(the yellows wiring is fine, it is the headlight circuit that is broke)
also, the back up lights dont turn on --- might be bulb.


anyway, i took my tester and tested all fuses. they were all fine. i went to the light itself and testing its prongs, all 3 wires read 0v, dead.

so this leads me to believe that i might have an issue at the panel that connects teh firewall to the cab BEHIND the fuse box. i took a glance at the wires int he dark and they did seem to have quite a bit of build up. I decided i was going to pull some of the wires to do some basic troubleshooting on the connections there.

My question is - is there anything i need to know to bring, or to not do concerning that firewall/cab connector box? or anything i need to be aware of when removing the fuse box to gain access?





also a side question -
my dashboard is blue, instrument cluster black, and teh metal under both (glove box area, or under steering wheel) is blue.
does vinyl paint typically do just fine on the dashboard? I was going withj black - should i go with a mat/flat black, or gloss? I was thinking mat/flat.
and what kind of spray paint would be passable for the metal parts? should i just skip the idea of doing a spray and wait until i can do a more proper job? i was hoping to do a quick easy simple job to last me about 3 years until i got to painting it.

this question also applies to the doors.

[tard01]

this is a 75 chevy c10

[88Jimmy4x4]

There is a center bolt that holds the 3 harness's in the engine bay to the connector. Remove that bolt and then the engine harness large connector. This is how I did my 76. They do sell replacement harness for each if your so inclined.

[tard01]

those harnesses are fairly expensive though right?


glad you told me there are 3... i only suspected maybe 2... wasnt even sure if the cab/firewall were split, thought htey might be a single piece.

this is new territory for me... when i inspected it, it was dark outside, so i walked away until i could get some sun to inspect it properly ratehr than make the situation worse.

trying to get knowledge before i give it a go tomorrow.

[tard01]

didnt see pictures on my first reply... those pics help since i wasnt able to get a pic last night.


i was hoping to find out what kind of connectors they use.... if i could scrape away the crud to get an exposed metal to test with a probe, that'd be extremely valuable... but i wasnt sure since there was so much crud last night.

do these punch down, or just slide under a screw/bolt/washer?

[88Jimmy4x4]

I paid like $115 for my engine harness, headlight is more I think.

heres the schematic for my 76, should be same as 75

[tard01]

ah, those pictures are gold - so much better than the wiring diagram i had previously... i had the diag for the next years up ... it also wasnt color coded, which while not necessary, still makes life a lot easier.

thank you.

i already used the other diagram i had to troubleshoot my stuff and isolate the failure down, but this certainly helps regarding the pin connectors. i didnt have that- i manually traced the cables visually.

[tard01]

i think i found a gold mine for my purpose...

http://www.rowand.net/Shop/Cars/1975...ingChanges.htm

[ont_guy_38]

Before you get too carried away check your dimmer switch, 9 out of 10 times that is why you get no headlights with the floor mounted one. Uplug the wires from the switch and get your test light and see which wire is the power then just jump that wire to one of the others and you will have lights if that is the problem.

[tard01]

hrm... that sounds worth checking. i havent done anything with that switch yet as far as testing. at teh risk of making a fool of myself, i only found out moments ago what that floor thing was (dimmer switch).

combining that with what you said... not entirely sure what i could tie it onto, but i imagine i can probably figure something out....

unsure, but at least i have something to check/chase.

[ont_guy_38]

There is 3 wires attached , one is power supplied and the others just go to low or high beam.There is no ground wire.

[tard01]

ya, i see blue, brown, and green... fortunately i have a pic of it on my phone i can see from work.

so i assume green and brown (tan) go to headlight since thats their colors -- i can assume teh blue is likely my power (will verify with tool).

so if i just touch/tie the blue/power to an active power and leave the other 2 connected to the switch.... does that mean i just get stuck with whatever beam its using? or does the switch somehow still function?


what your saying sounds more and more likely combining the other tests i've done.

[ont_guy_38]

no you have to connect the blue (if the blue is the main power,which you are probably right) to one of the other ones once you verify you have power with the light switch on

[tard01]

Going through everything in my head combined witg what I've tested prior, I feel pretty certain you're right and the switch is likely my cause... I'll do a simple test of it when i get home in a few hours and let you know.

I certainly appreciate everyones willingness to help me. This is my first project vehicle... Ive mever worked on anything more than 7 years old, so this is ky learning curve. fortunately ive got some basics for a foundation using modern cars.

I might have this truck legal after this next week, if I can gwt tires here.

Now if this works ill need to just figured out my back up light
Posted via Mobile Device

[tard01]

So the dimmer switch did end up being my root cause. headlights worked afterwards.

i then set my sights on the brake/park lights, back up lights, and blinkers..

i was testing electric signals at the last connector on the wiring harness before they go itno the lights (behind the license plate) and found that the previous owner had opened it up and attempted to make trailer signal lines... unfortunately it appears they tried a few different methods in doing so. i found several oddities when looking. he had used tube splicers to combine 3 wires... and i was getting power/volatage on my ground connections... he also had a few wires just randomly hanging out and taped off that i couldnt identify where they went since the grounds were bad.

I mapped which pins i felt were doing what and how should i see certain signals coming in and noticed that one of the pins never went hot that i'd expected was the back up light. I went and looked at my shift column and found that not only was the shift indicator was removed completely, but i didnt see electrical going to it... so i didnt know which of it was correct. I went to the parts store, got a neutral/back up switch and came back.. then realised on the 75 that it was way at t eh base of the column, but i still found no electrical wires for it... i saw a light green plug hanging, assumed it was it since it would fit one of the pins and i was expecting a light green at the rear... plugged it in (tight space!) and finally got voltage to the rear, but not to the light.

in the end, i decided to just suck it up and pull out the wiring harness and just rebuild it. I'm so glad i did... i ended up finding all kinds of weirdness and bad contacts/splicing attempts.

I cut off all the connections he messed with and added onto... and i basically just rebuilt the pre-existing wiring. Fired up the truck and first try my lights all worked. brakes, parking, reverse, blinkers...


i had a current/power drain on the system when running lights + blinker was used... i saw a lot of corrosion on the lights themselves, so i went to the store and bought new lights. that fixed the power drain. i assume the rust/corrosion on the bulbs themselves was sucking away power because after that, everything was gold.




I appreciate the help with the dimmer switch - that one would have probably stumped me for a bit, even if it is a simpler fix.

i got my truck inspected the next day, passed. now i get my registration on wednesday. i took the dashboard/console/instrument panel out opf the truck last night and cleaned it all up. will be painting it shortly.

i figured out a paint scheme i wanted to run with, but i cant seem to find a spray can that has the color i want. will have to research.

(wanting to do a deep dark graphite/charcoal gray on the dash - i assume the material is vinyl)

[zosoppp]

If you need a trailer connection I suggest this type, no cutting/splicing required (for 67-72 specifically):
Not certain if it's a match for squarebody era connectors, but there's probably something similar.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[hatzie]

Originally Posted by zosoppp

If you need a trailer connection I suggest this type, no cutting/splicing required (for 67-72 specifically):
Not certain if it's a match for squarebody era connectors, but there's probably something similar.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

X2 on those Hopkins trailer plug-in units.

The 84-91 CK/RV & 88-02 T400 have Weatherpak plugs back there and Hopkins makes plug-in units for those as well.

I usually expect and find U-haul and Ryder Hitch-Monkey wiring jobs using Scotchloks and open butt splices that have completely destroyed the tail lamp harnesses on any trucks over a few years old.

If your molded plug taillamp harness is badly damaged close to the molded plug you'll find it's not available. You can fab an upgrade to the 1984 and later CK/RV chassis square 2x2 four terminal Weatherpak fairly easily. The four wires are solid colors so all you need is tooling, split poly loom, SXL wire, Weatherpak parts, and the Packard 56 terminals for the bulkhead plug.
The pinouts for those plugs are in the FSM wiring diagrams in my sig.