86 GMC Sierra Classic 2500 questions

[motornut]

do yourself a favour and get rid of those blue connecters
they cause lots of probs, basicly cutting wires,allows moisture/salt in
they prob used it to connect a trailer harness.
may have removed the plugs too.
the cluster dimmer is controlled by a coil of wire that can burn out in spots,
a rheostat,if the switch is out (of dash)you can usally see it,might see the burn marks too
thats why it can work off and on when twisting the nob
the od goes to 99,999 then 0,later years have another digit

[csdineley]

99999.9

[gmcnoob]

I bet this one rolled past 99,999.9 about 5 or 6 times by now.

When I was messing with the headlight switch under the dash I did actually notice a little melted plastic on the switch.

[Keith Seymore]

Originally Posted by gmcnoob

one other thing i wanted to ask about the odometer. Mine is at 45,000 miles... Obviously it reached it's limit and started from zero again. It's probably more likely to be at 345,000 or more miles. How high do the odometers go on these trucks before rolling over to zero again?

99,999.9

k

[gmcnoob]

I always realize how dumb some of my questions are after it's too late. It should have been obvious how high the odometer went since there are only 5 digits + the 1/10.

[gmcnoob]

I have searched all over this site an have not found a solid answer to this issue. So there is some kind of vacuum valve right above the brake pedal and when I press the brakes it makes the hissing noise. I have read a lot about bad boosters, etc but the brakes seem to be working great and I really do not think it is a bad booster. I saw one post where a guy said, "it was a vacuum plunger like switch that was connected to the brake pedal. I guess it was used to kill the cruise when the brakes we engaged."

Apparently he just disconnected the vacuum line that led to just above the brake pedal and it solved the hissing problem. On my truck "electronic speed control" was one of the options. I assume that is the same as cruise control... Was he correct? Was this just something to disengage the cruise control?

[motornut]

yes follow it and it will end at the CC under the hood(my 88)
not using it?be sure the other lines are sealed off too

[gmcnoob]

Interesting. I'm not sure what the previous owner had going on but on my truck it let to right behind the carburetor. This setup is how I bought the truck and I want to make it right. Please take a look at the picture and let me know if this is correct. Should I remove the line leading to the cruise control switch and cap/plug it?

[gmcnoob]

Well, I removed the vacuum line for the cruise control and capped the valve coming from the intake and no more hissing. Thanks to all of the help that I've received here the truck is running better than ever. The brakes work great! I'm proud to say that I haven't had to bring the truck to a mechanic thanks to you guys. This truck is the first vehicle I have ever fixed other than a Husqvarna mower. I realized that you just have to dive in and do your best and learn from your mistakes along the way.

Yesterday I replaced the distributor cap, rotor, wires and plugs. She fired right up. The old plugs didn't look too bad but they fell into the oil fouled category.

I finally found the rare tire size at tire rack (BFG 33x12.5x16.5). They are supposed to be available today so I ordered them. The old Wranglers on there are dry rotted. The delivery fee wasn't nearly as bad as I expected. Ended up paying around $220 per tire with taxes and shipping included. Should have them on next week, I hope.

Now all I have are pesky electrical issues. One day the wipers will work, next day they wont. Sometimes the rear lights work, sometimes not. It's very frustrating.

[motornut]

glad you got it.
I found pics of the 88 harness loose, but I see you figured out the switches.

[gmcnoob]

So, Tire Rack called and apparently BFG pushed back the manufacture date of these tires , "at least a month". I just can't win.

I thoroughly looked over the electrical system and as far as I can tell everything looked good but I must be wrong. I installed a new headlight switch and now the instrument cluster lights are brighter than ever. But now the strangest thing happened. I turn on the right turn signal and it flashes along with the left rear side marker. What? Why would the left side marker flash along with the right turn signal?

I'll take brake problems over electrical issues any day. The only thing stopping me from hitting the road are the rear lights.

Anyone in VA want to come over and fix this? I have some cash for you.

[motornut]

weird I'd check the light grounds

[gmcnoob]

Originally Posted by motornut

weird I'd check the light grounds

Would you happen to be able to tell me exactly where to look for the light grounds?

[motornut]

Originally Posted by gmcnoob

Would you happen to be able to tell me exactly where to look for the light grounds?

front headlights are just inside the fenders
rears pull the tail lights
if the big batt has a poor ground it can fry the other smaller ones

[gmcnoob]

You are the man! Thanks for helping a noob out!

[motornut]

Originally Posted by gmcnoob

You are the man! Thanks for helping a noob out!

no prob glad it helped

[gmcnoob]

Well, I checked all of the grounds. Loosened them and hit them with a wire brush real good and reattached them nice and tight. Everything works including the license plate bulbs which is a first. Now it doesn't matter which turn signal I turn on all of the rear lights flash including the license plate bulbs. Everything in the front is working correctly. Brake lights work the way they're supposed to, reverse lights work. Either turn signal has all of the rear lights flashing. I am baffled.

The only electrical things that I have ever messed with on this truck were replacing all of the fuses and the headlight switch.

[motornut]

Originally Posted by gmcnoob

Well, I checked all of the grounds. Loosened them and hit them with a wire brush real good and reattached them nice and tight. Everything works including the license plate bulbs which is a first. Now it doesn't matter which turn signal I turn on all of the rear lights flash including the license plate bulbs. Everything in the front is working correctly. Brake lights work the way they're supposed to, reverse lights work. Either turn signal has all of the rear lights flashing. I am baffled.

The only electrical things that I have ever messed with on this truck were replacing all of the fuses and the headlight switch.

I think you may have a crossed wire...
brown should run licence plate and tails/markers.
any other sign of hacked in wires?
they run from the firewall engine plug/frame /to the back

[gmcnoob]

These electrical issues are driving me nuts so whenever my new tires finally come in I think I'll just have the mechanic figure it out. I have attached another picture of the rear wiring after removing the electrical tape. All lights are getting power and everything seems to be going to the right place. Picture 1 is where the main wire splits at the rear. Picture 2 shows where the wires were messed with by the previous owner. Any thoughts?

On to the next thing.... In the meantime I will start on some interior renovations. I was thinking about using Dupli-color to renew the door panels in black. The old faded mahogany color looks terrible. Has anyone used this product? It says you can use it on fabric, carpets and vinyl.

[motornut]

Originally Posted by gmcnoob

These electrical issues are driving me nuts so whenever my new tires finally come in I think I'll just have the mechanic figure it out. I have attached another picture of the rear wiring after removing the electrical tape. All lights are getting power and everything seems to be going to the right place. Picture 1 is where the main wire splits at the rear. Picture 2 shows where the wires were messed with by the previous owner. Any thoughts?

On to the next thing.... In the meantime I will start on some interior renovations. I was thinking about using Dupli-color to renew the door panels in black. The old faded mahogany color looks terrible. Has anyone used this product? It says you can use it on fabric, carpets and vinyl.

i'd try to clean those blue connectors right out,confirm that there is no black wire stuck in with the brown.
if you unplug the firewall plug you could run tests from there.

[gmcnoob]

Originally Posted by motornut

i'd try to clean those blue connectors right out,confirm that there is no black wire stuck in with the brown.
if you unplug the firewall plug you could run tests from there.

Thanks for the advise. Maybe I'll just remove the connectors entirely and reattach the wires. There is no black in with the brown as far as I can tell but the 1 brown wire is split into 5. Two to each side and 1 to the license plate lights.

I painted the drivers side door panel black yesterday and it looks bran-new. I will try to get some before/after pics. I decided to do all plastic pieces in dupli-color flat black and the fabric and carpet pieces on the door in charcoal gray. I hope it turns out... Anything would be better than what it was.

[gmcnoob]

Pics of new interior color. I think it turned out pretty well. The pouch ended up looking gray while the other fabric turned out a darker charcoal gray even though the same paint was used. I still think it works though.

[gmcnoob]

Moving along with my maintenance while waiting for these stupid 16.5" tires to be manufactured... Decided to do a coolant flush yesterday. Surprisingly what drained out was fairly green considering I have not changed it in the 5 years I have owned it. Oops. I'm learning cut me a break. The flushing part yielded massive amounts of rusty looking water that just kept coming out. It didn't appear to be oil, at least I hope not. I kept flushing until the water came out clean, then filled it up with just water and brought it up to operating temperature with the radiator cap off as that's what I read you were supposed to do. I added some more water as it lowered a little bit and what do you know, more rusty water. I let it run for a bit longer then the water did not drop anymore so I put the cap back on and let it run for a while. It was getting late so I shut it off and I'm going to drain it again today. Is all of this rusty water normal for a truck that has been sitting unused for quite a while and not flushed for at least five years? I heard this may be a sign of a blown head gasket but I don't have any other telltale signs of that.

On another note I live out in the middle of nowhere and there are a lot of rough old logging roads that I can test out my four-wheel-drive on. Even with the tires in the sorry shape they are in the truck impressed the hell out of me and my buddy. I went into a bit of a dip that was a little deeper mud than I had expected. It got stuck so I slapped it in 4 low and it crawled out of there no problem. This was with mud up to about 6 inches from the rear bumper. The truck now looks brown it is so covered in mud, I love it.

I wish I had started working on this years ago but since I'm not a mechanic I was intimidated. I seem to be having good luck fixing things lately. I'm having lots of fun and learning a lot. I'm just about done with any mechanical issues so the rest is just cosmetic work. Thinking about going on Craigslist and finding another one around the same year to fix up.

I'm probably just rambling to myself here but thanks for listening.

[gmcnoob]

I'd also be interested to hear anyone's thoughts and recommendations for a carburator I could slap in this truck while I get the Q-jet rebuilt.

Also any suggestions on exhaust. I like a mean sounding truck but nothing too ridiculous. The mufflers are rusting apart and exhaust might be my next project.

[gmcnoob]

Good morning. Can anyone tell me what this little black box is/was for on the left side of four-wheel-drive?