1987 Suburban Dash problem

[diesel2006]

Pardon me. I am a new user. I have a 1987 Suburban (6.2L) that had an alternator go “high voltage”.
Voltage, oil pressure, and fuel tank gauge stopped working.
Folks talk about some type of module that may have been blown. I have removed the dash twice (replacing bulbs and repairing the shift indicator) but have failed to locate such a module even after following the wiring harness. If there is such a module, how big is this “animal”? Thank you.


Diesel2006
1987 1/2ton Suburban 6.2L

[DmaxMaverick]

Welcome aboard!

The "module" you are looking for is inside the alternator. It's the voltage regulator module. The very same part the two spade connector connects to at the back of the alternator (the regulator is at the other side of the spade contacts).

If your only issue is "high voltage", then a regulator replacement will usually fix it for a long time. As long as the alternator spins smooth and quiet, it should do it. The alternator does have to come apart, but no big deal. Once the looooong case bolts are removed, the case will halve, and the regulator is at the bottom secured by 2 screws. Replacement is no more difficult than that. On reassembly, use paper clips or tooth picks to hold the brushes back while the armature (the large internal "spinning" part) is inserted into the rear bearing (there are holes in the case bottom just for that purpose). Push the brushes into their slots and insert the clip/pick into the hole. The brushes should be held against the spring tension, and well clear of the commutator (the part of the armature the brushes contact) when you insert it. Remove them before installing the alternator into the vehicle.

Let us know what you find, and how it works out. Good luck!

[Robyn]

If I am reading right, you have replaced the bad alternator but the instruments are not functioning???

I have an 86 Burb shop manual (Factory) and it does not mention any module.

Check as follows
Be sure there is not a blown fuse in the fuse box. (20 amp 4th row up from the bottom of the fuse block and 3rd from the RH side of the fuse block)
If fuses ok then remove the dash bezel to get at the cluster.
These clusters can easily be disassembled and individual gauges replaced.

Get the cluster out (there is a large plug on the back plus the spedo cable if its not electronic)

Once the cluster is out, check the printed circuit (mylar trace panel) on the back of the cluster for any damage.

If the mylar is good then remove the front of the cluster (clear lens) and this will allow you to unplug the gauges in question.

Start with the volt meter. Unplug it and check it to battery voltage.
The studs are marked on these so you can use a set of wires with clips and connect the gauge to a battery on another rig thats running to see if it reads normal 13.5-14V

If the gauge reads ok then its the feed circuit to the gauge.
You can plug the cluster back in temporarily and check the feed to the volt meter studs with a VOM

If this shows no response then the feed to this circuit has been damaged.
The fuse is my first inclination but anything is possible including an ignition switch.
There is also mention of fusable links within the wiring harness itself but I have yet to find any directions to this as far as the instruments is concerned

One step at a time though.
The oil pressure and fuel gauges have sending units that could have been damaged too.


If the gauges are bad I have some good used gauges I can fix you up with very reasonable.

I assume that all other electrical equipment on the rig functions OK ??


The temp gauge is working OK??

Let us know

Robyn

[diesel2006]

First REPLY first.

Dear Dmax,

Since this 6.2L Burb was my first Chevy, I didn't know if the Alternator I removed was the correct configuration. Trusting my local NAPA way too much the alternator I received was NOT THE SAME configuration and hense didn't want to bolt up. (I realize now what error I made, I should have retained the original alternator "case" because it was clocked to fit my application.... The new NAPA Alt was not the correct configuration.)

WELL..... I am an Aerospace Engineer, and well nothing is impossible. The NAPA case is installed and nearly perfectly aligned (Aerospace measuring technique). I had an initial problem with tightening the belt too much (I was accustomed to FORD 1984-1994 6.9L/7.3L installations), but the new alternator appears to be operating fine.

The gauges are dead in the water. I believe I measured the voltage from the "broken" alternator at 25 Volts (HIGH ORDER!) before I removed it.

I think I understand now that when I removed the "broken" alternator, the case should have wanted to come apart. It didn't.... And NAPA handed me their answer for the application. Nobody mentioned the alternator case coming apart....................................... Nor did my diesel manuals.


Thank you Dmax. My Chevy/GMC Assessories World just expanded 10 fold.

To Ms. Robyn, I will REPLY to your input next........ and thank you.

Sincerely,

Diesel2006
1987 6.2L Burb

[rhsub]

where are you located
a friend of mine has a 85 sub 6.2 that he is scrapping
let us know
Ron
ps I would check batterys and connections. battery is stability in charging system, for you to have charged 25v batterys or connections are probably bad. This is why service manual says do not disconnect batterys when engine is running, alternator can charge 40v without battery in system and fry all your electronics

[diesel2006]

Hi Ron,

I am currently moving things around in Arizona, New Mexico, Texas and Colorado. I am getting ready to move to Anchorage, Alaska.
That's close to Canada. lol

Where is the 85 Sub?

Richard
diesel2006
87 6.2L "Burb"

[diesel2006]

Hi Robyn,

Thank you for your REPLY.
1. I took apart the dash and inspected the mylar trace panel. I checked every trace for "contenunity" (that word) and I believe every trace passed.

2. Voltage gauge is dead. As far as I can tell the temperature gauge is also shot. The Fuel gauge is shot, and of course the oil gauge is shot. I am not getting any "signal" to any of these connections when vehicle is running and gauges have been removed (prior to starting) from their plugins.

3. I suspected sending unit(s) problems, Just wanted to know about the "magic module" that supposedly fed the dash. Have to run.

thank you and Dmax once again,

Sincerely,

Richard
diesel2006
87 6.2L "burb"

[DmaxMaverick]

There is no "module" for the instrumentation that I'm aware of. The circuit supplying power to the gages is fused, though. If you are not getting a signal to any of the gages, I'd suspect the INST circuit has either lost contact somewhere (fried wire/connector, etc.) or a fuse has blown. You have checked the fuses...Right? Is there anything else on the truck that doesn't work now?

[diesel2006]

Dmax,

I lost voltage gauge, oil gauge, temperature gauge, and fuel gauge (important one). No other electrical was effected/affected. In aviation;
"I've lost me instruments"........... Fuses checked.

I may opt for a set of gauges, then "plug and play". Right now its moving time. Just have to fly "blind" for awhile. The Burb has the 40 gallon tank, I just need to watch the trip miles and fill up accordingly. I do remember trying to get a "signal" from the wiring harness. Seemed I wasn't getting anything from the connection (when vehicle was running) which re-enforced theory about a "module". I think I can take another look at it this weekend (I hope).

thank you

diesel2006

[DmaxMaverick]

Hmmmmmm....

If the gages, and only the gages stopped working, the problem has to be something common to all of them, and only them, and it isn't likely they all fried at once. Did you verify your ground at the circuit board? IP connector? I'll have to have a look at the diagram for a common point of failure.

Good luck VFR in the meanwhile.

[rhsub]

Richard
85 Sub is in Peterborough about 80 miles north east of Toronto, have not verified that he still has truck but his son has a 80 1 ton so I am pretty sure they are keeping it for spare parts, will call tomorrow

Checked wiring diagram
temp, oil and fuel guages have 3 terminals each

circuit 39 power, circuit 150 ground (black wire. may be 3 seperate terminals in IP plug) and 3rd terminal to sending unit

Circuit 39 is a pink/black wire, 12 V with key on, should be 3 in ip plug, they get power from guage/idle fuse in fuse box when key is on, this fuse also powers fuel heater in filter, brake switch (tcc??), buzzer, water in fuel, low coolant module, and trans kickdown (400), caution pink/blk is also the ecm1 fuse wire colour

circuit 35 dark green, coolant temp sender,
circuit 31 tan, oil pressure sender
circuit 30 pink, fuel sender
should be variable resistance on these 3 circuits depending on engine temp, oil pressure etc

voltmeter takes bat + from cir 39 and grounds on cir 150

To check individual guage, apply 12 v to + term, ground - term, and temporarly ground sender term, guage should move full scale, (high no grd, low grd, I think)

There is no module (chrysler uses a voltage regulator in there IP)
Hope this helps you clear up your problems, its actually a basic system once you get your head around it
good luck , I know how I hate driving with no guages
ron