Author Topic: A little light, heater and instrument cluster help  (Read 1732 times)

Offline Matt9278

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A little light, heater and instrument cluster help
« on: January 16, 2020, 09:01:33 AM »
Hey everyone! Iíve been creeping discussions for a while and have found a lot of awesome info! I will be diving into this again tomorrow but decided to try and get some more insight from you all.

1983 gmc high Sierra
4spd
4x4
350
A/c but it has been hacked apart and is no longer functional

Keep in mind itís January in South Dakota and after work when I get time to work on it, it is about 2 degrees and I lose motivation fast haha. I do not have a repair manual for these yet but would be open to suggestions on which ones to get.
 
I bought this pickup as a fixer upper for my son with what I was told by the owner had a ďbad engineĒ. With a little elbow grease, plugs, cap, rotor, wires, and fuel pump I have it running like a top now. So we are at the point that I have trouble with, electrical. I did a quick survey and had headlights, left rear running light and left side marker. Other than that everything was dead. Changed a few bulbs and cleaned the plug that is in between the tail lights and all Iím missing now is right brake/turn signal and reverse lights. The right turn signal is VERY intermittent. I took the flashers out and switched them around with no change so I shorted them across with the same result. I guess my question is where exactly is the ground for the tail lights? Iím thinking thatís the issue.

Now to the dash. I have lights but oil pressure, engine temp and volts do not work, found what I believe is the ground for it just in front on the e brake on a 6-slot receptacle I guess I would call it? Iím not sure. Also Iím sure this is a ground issue as well but Iím not sure if Iím looking at the right one. I tried two panels and switching the gages around from one to the other with the same result.

Now to the heater. I kind of need that fella this time of year haha! I havenít had much time to tinker with it because of lack of motivation in the cold but from what I can gather is Iím getting heat but itís not blowing. I tried it with the engine off and I couldnít hear the fan ďramping upĒ as I would call it. I have very faint heat coming out of the dash vents. First thing tomorrow Iím going to rip into that but in the mean time I wanted to ask do these pickups blow a lot of air or is it faint like I described?

Iím going to include a picture as a reference to the dash ground Iím talking about.

Thanks for the help

Offline zieg85

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Re: A little light, heater and instrument cluster help
« Reply #1 on: January 16, 2020, 09:23:31 AM »
The ground for the tail lights is behind the left rear light assembly.  You have to take it completely out for access.
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline zieg85

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Re: A little light, heater and instrument cluster help
« Reply #2 on: January 16, 2020, 09:29:59 AM »
Verify the wires are connected to the temp and oil sensors.  I believe there is a gauge fuse and yes that block pictured it the ground for the interior wiring.  Verify the plug is secure in the speedometer cluster.
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
https://www.facebook.com/groups/248658382003506/

Offline 75gmck25

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Re: A little light, heater and instrument cluster help
« Reply #3 on: January 16, 2020, 12:28:39 PM »
On older the trucks (like my '75) the instrument panel is grounded to a post on the emergency brake mechanism, but on newer trucks they use the ground point shown in your picture.  Failure to ground the panel will cause all kinds of weird behavior as devices find a path to ground.  Replace that ground ASAP, and then continue to  troubleshoot.

The lower blower speeds are controlled by the dash switch and the resistor pack that is mounted in the A/C plenum under the hood.  The high speed is a direct feed to the power point near the brake booster, but is controlled by the A/C relay in the plenum under the hood.

On high dash switch position or in A/C max it will kick in the blower relay and make the direct battery connection.  If its not working you may have a bad relay (not that common) or a blown fuse in the line under the hood.  Its fairly common to blow that inline fuse as the blower motor gets old and draws too much current on high speed.  In my experience, the only really strong speed on the blower is high speed.

Bruce

Online bd

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Re: A little light, heater and instrument cluster help
« Reply #4 on: January 16, 2020, 02:33:14 PM »
All of the factory GM manuals you should ever need: 1973-87(91) Factory GM Pickup Manuals.  You probably should take the time to download the relevant manuals to your hard drive for convenient, anytime access.

To augment what has already been posted, the blower motor should run continuously on low speed with the ignition ON and the fan "shut off" by the dash switches.  This is done to minimize mildew development in the vents.  Low speed provides nearly imperceptible airflow.  High speed is barely adequate in extreme weather conditions.  If debris clogs the ducts behind the dash (a common situation), airflow can be severely impeded. 

Typically, high blower speed is protected by a dedicated 20-amp inline fuse that connects directly to the firewall junction block mounted above the back of the engine near the brake booster.  The plastic fuse holders often melt and distort due to poor electrical connections with the fuse combined with the high current demand of the blower motor.  Distortion of the fuse holder often defeats high blower operation. 

Low and medium blower speeds (as well as the high blower relay coil) are separately protected by the heater fuse located in the fuse box inside the cab.  Although all power supplied to the blower motor flows through the high blower relay mounted under the hood, the relay itself energizes only when high blower is requested by the operator.

To check the blower motor, temporarily connect a B+ jumper protected by a 25-amp circuit breaker directly to the blower motor terminal and see how the motor responds.  For further help with diagnosis, we need to know exactly under what conditions the blower operates and doesn't operate, whether the blower is unusually noisy, etc.

(Edited for improved clarity).
« Last Edit: January 16, 2020, 08:26:35 PM by bd »
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Matt9278

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Re: A little light, heater and instrument cluster help
« Reply #5 on: January 17, 2020, 04:04:43 PM »
Wow awesome info and thanks for the manuals link!! I finally had a day off and got to work on this thing. Looked at the blower motor under the hood and found the purple power wire unplugged! Easy fix haha!! Moved on to the lights situation, I did find the ground mounting location. It was horribly rusty and covered in dirt. Took that apart and wire wheeled everything clean. Took some dielectric grease slathered it all over and slapped it back together. No change yet. I ran out of time dorking around today and the weather got too cold so hopefully tonight or tomorrow I can check continuity between the two sides and go from there. Next after the lights get fixed will be the dash. Hopefully I will have some time to work on it this weekend.

Anyone else use dielectric grease? I learned to love it while chasing ground faults on my vw!


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Online bd

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Re: A little light, heater and instrument cluster help
« Reply #6 on: January 17, 2020, 07:14:12 PM »
Looked at the blower motor under the hood and found the purple power wire unplugged!

That's hilarious!!!   :)
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)