I have some weird things going on with my '85. I was initially convinced it was a bad ground and it still may be. But things have got worse lately. The short story is that when I used to turn my heater control to any position except "OFF", the oil pressure and voltage gauges would drop and the temp gauge would go up. Eventually, I found that if I unplugged the blower motor relay, all was well. So, I replaced that relay. That lasted about a day. I then noticed that I'd get the same symptms if I turned on the winshield wipers. The wipers and blower motor appear to share a ground so that made sense (I guess...). The wipers have had a tendency to just shut off from time to time so I ordered a new switch which I never got around to installing. Now, last night and today, in the rain, my dash goes dark as soon as I either turn on the wipers or heater. Not only do I lose the dash (goes completely black) but my wipers or heater will not work. I replaced the wiper switch and still have the same problem. Now, here's the wierd part - after sitting a few minutes, all will come back. Sometimes when it comes back, all my gauges read normal - sometimes they read weird. I'm not blowing any fuses but am obviously tripping something which resets itself.

Anyone have a clue? :smash:

Thanks...

 

Sounds like a loose ground somewhere; start checking them for a loose or frayed wire.

 

I'm really at a loss as to where to start looking. I currently have the dash apart but all looks well back there. The ground wire from the left head "looks" OK. My service manual isn't as clear as I'd like it to be. It shows the blower motor and the dash and the wipers sharing a ground behind that left head, but the wires coming out of the blower motor relay are much larger then the wires attached to the head.

I'm lost... :(

 

Your problem sounds very similar to mine. I also have an 85. Whenever I moved the climate control to anything other than "off" the oil pressure would drop 20 psi and the water temperature would raise 20 degrees. I would also lose about a quarter tank of gas. One day, I turned on the air and the dash went dark. Wipers out, odometer out, heater fan out, etc. It would flicker on ocasionally and then died completely. I took it in and it was found that ground G140 was bad. Not only was it bad at the point of connection, the wire had also chafed inside the wiring harness. They fixed that (don't ask how much it cost :eek: ) and the problem went away. One piece of advice - if you rip apart the dash to fix it, replace the heater core at the same time. Mine went out two weeks after the ground was repaired and they had to rip the dash all apart again to replace it. If your car is like mine, it's on its way out and you won't have to pay labor twice! Good luck and open that checkbook wide! :)

 

Do you know exactly where it was chafed?

Thanks...

 

Sorry - I don't. I remember them saying they replaced a section of the ground wire inside the harness, but that's it. It would seem like that's your problem; it would explain why it works intermittently. Could you just replace that single entire wire from the frame to where it terminates? (Sorry if that's a stupid question - I'm not a mechanic). :)

 

I could replace a wire if I knew where it went to... I found out on ChevyTalk.com that there are a bunch of ground wires under the left side kick panel under the dash. I'll check there in the morning.

Thanks for the info. :yesnod:

 

The windshield washer motor and the blower motor share two ground connections. G109 which is on the frame just ahead of the a/c evaporater housing on the RH side of the engine compartment. The other ground they share is S116 which is inside the wiring harness right by the blower motor. You can access S116 by following the ground wire from G109 on the frame up through the wiring harness. Your symptoms coincide with either or both of these grounds. The easiest one to clean up and reconnect is G109.

 

Do I have to jack the car up to find G109?

 

OK. Here's where I'm at:

I didn't mention previously that I have a coolant leak in the vacuum operated valve in the piping just above the blower motor. I noticed that there was coolant on the blower relay so I replaced it. There is also coolant on and in the wiring harness just below it. (Those wires feed the blower relay among other things.)

With the blower relay removed, I have around 3-4 volts on the hot wire of the blower motor. (That wire gets its power through the blower motor relay...)

The ground wire for the blower motor, when disconnected, has 12 volts on it. This wire does not go through the relay.

If I ground the ground wire for the blower motor, the windshield wipers and dash all work correctly.

I must have some wires chafing or the connector inside the harness near the blower motor is corroded with antifreeze. Plus, the connector for the blower relay must be toast???

Not blowing any fuses... :confused:

Think?

 

A direct short from +12v to -12v will blow a fuse. A open circiut (bad connection) in the wrong place, or sometimes water shorts under low amperage can cause grimlins.

 

According to the shop manual G140 (grounding point 140) is located on the lower LH rear of the engine. It feeds the blower relay, blower motor and the wiper motor/washer. I would head for this ground point and make sure it is tight. There is also a splice (s115) located in the engine harness above the rear of the LH valve cover.

HTH.

 

Your problem is clearly a poor ground connection through G109. G109 is on the top of the frame just ahead of the evaporator housing on the RH side of the engine compartment on the firewall. G109 is a single bolt with a single wire and lug . Your antifreeze leak corroded the crimp of the lug on the ground wire or the frame or both. Fix the corrosion, fix your problem.

 

Thanks to all who have replied. Misery loves company and this is the place for good company! :)

jfb: I cannot find G109 to save my life. I've removed the inner fender well and still can't find it. My ground wires go into the wiring harness and under the engine into the main harness through connector C190. My GM service manual does not mention this ground. Is your car an '85?

I think that my problem is probably a bad S115 splice or an open circuit somewhere between S115 and G140. I'm saying this because the ground wire on connector C190 carrying the main ground from G140 to the blower motor is not grounded. According to the wiring diagrams (and gdarwin :) ) G190 connects the grounds for the blower motor and windshield wiper motor to G140 through S115.

So, here's my question:

There is no easy way to troubleshoot this wire. I can barely access G140 (which is tight). The harness is behind the engine. I just had my trans rebuilt a few months ago and am now wondering if that has something to do with all this. They did a poor job at everything else; they could have easily damaged that harness... Anyway, I am wondering if I can just connect a new ground wire from the frame to the blower motor ground as a permanent fix. Doing this on a temporary basis gets everything to work. Do you think this would hurt anything?


Thanks again for all your help. :yesnod: :lol: :smash:

 

I have an 87 and am reading my 87 electrical service manual. There is nothing wrong with grounding your blower motor at another point and I recommend it.

 

Thanks!

I'm going to splice in another ground.

I wonder if what I'm seeing was a known problem early on which caused GM to add that G109 to later years???

Thanks for all your help and quick replies.

 

Did your plan to add another ground wire work? I hope it did. Let us know! :)

 

I work nights and my commute is 100 miles round trip. I didn't want to report anything until I got home this morning and knew one way of the other how the fix went...

Adding the ground (with a 12 gauge wire) went a long way towards eliminating my symptoms. My oil pressure still drops around 5-8 pounds when I switch on the heater, but everything else is fine. (It sometimes comes back up to mormal with the heater on.) I can run the heater and wipers at the same time and my dash does not flicker. :yesnod: :lol: :D

I think my next step is to ground the dash directly and then I should be good to go.

If I had to guess, I'd say that the splice which ties in the blower motor/WSW to the dash is suspect. (Or the main ground wire going from that splice to the engine G140.)

Thanks to all of you for your help. :cheers:

 

i have no power from the guage fuse to my alternator!Yikes I can'tgo anywhere like that
So i find that the fuse goes to a junction called s115, but I can't find it.
any ideas for u electrical gurus
i'm thinking of rewiring to another ign fuse crkt
Thx in advance

 

LEW, i'd suggest a new thread dedicated to your problem. Cheers. VT.