Rear Window Defogger

[starfire]

OK, I'm following the RWD Diagnosis chart in the CSM. My indicator lamp works when I put 9 volts to it, but does not light up when I turn the switch on in the car. So the next box in the chart is "Check in-line 3 amp fuse in BROWN wire from generator to timer". I can find the brown wire, but I cannot find an in-line fuse. Anybody have any idea where this fuse might be located?

The schematic is not helpful as there is no scale to it. The wiring diagram does not show it at all.

Thanks,

Alan

[RustyPile]

Not sure just what you mean, but schematics don't have a "scale" to them. They indicate wire and component routing. Good schematics also indicate wire color codes and plug/connectors. Electrical part and component locator manuals will tell you where to find the various components.

Disconnect the connectors at the generator (could this be the rear window defroster control module) and timer. Using a Digital voltmeter, check the continuity of the brown wire. If you have continuity, either the fuse is good or there is no fuse. If there is no continuity, fabricate a jumper incorporating a 3 amp fuse. Substitute this jumper for the brown wire. If the indicator light and defroster work as they should, continue your search for the "missing" fuse.. As a last resort, and I do NOT recommend this procedure, make the jumper a permanent part of the wiring harness.


RustyPile

[Monza Harry]

Rusty, the factory schematic does show the wire's with colour and stripe info, and the connectors, however there is no location spec's that I have found in any of the 4 GM manuals or the Petersen's and Chilton Manuals or the schematics booklet (GM)! The schematic is drawn for the engineer's convenience not the end user. Some sections are laid out sensibly just not the main car, it shows the seatbelt reminder buzzer towards the back, etc. As these are the most difficult schematics I have ever used for instance a wire leaves a device and criss crosses all over the place and goes to a connector then the second half of the connector doesn't seem to match up with the first and the "bundle" that crosses the car is broken and the other section of the bundle has the wires in a different order so you have to look at the labeling to make sure you have the 22brdblwtst and not the 22brwtst. (22 Ga. brown double white stripe not....single white stripe) Anyway Alan
the defroster has a hot lead from the Alternator to the control module (next to the steering column, at the switch) as They (GM) didn't want the battery to run the defroster. I think I would check to see if the power is coming to the controller first, as per the schematic and then if good check the "Module" with a mock up and a test light instead of the back window, or better yet see if the power is going to the window first as the glass and connectors there can be problematic at best, I don't remember a fuse in that part of the harness but it has been awhile, I do remember quite a few fusible links in the harness as a whole and they can be a "BEAR" to locate sometimes. So Alan do you have the factory wiring schematic? Shoot me your no. by PM and I will see if I can help you out over the phone a little more interactive in real time. My cell plan includes 248, 313, 586, 734, 810,& 947 area codes as local and I have Magic Jack as well just can't walk out to the car that way. Harry

[starfire]

Harry, I have the Oldsmobile CSM and the Fisher Body manual for 1978, so I think I have all the info I need (other than where in the line that damn in-line fuse is .

I can see that the huge gauge wires that run from under the roof panels (the right hand one seems to be ground, the left hand one power) to the RWD itself have lost a bunch of their insulation. That may be my culprit right there, but if so, it's possible the fuse is then blown. It'll be a while before I get back to the RWD, I've decided to replace my standard steering column with a tilt, and I've run into a bit of an issue. That's a topic for a different sub forum.

Once I get back into the RWD I'll update this as to what I find out.

[RustyPile]

Rusty, the factory schematic does show the wire's with colour and stripe info, and the connectors, however there is no location spec's that I have found in any of the 4 GM manuals or the Petersen's and Chilton Manuals or the schematics booklet (GM)! The schematic is drawn for the engineer's convenience not the end user. Some sections are laid out sensibly just not the main car, it shows the seatbelt reminder buzzer towards the back, etc. As these are the most difficult schematics I have ever used for instance a wire leaves a device and criss crosses all over the place and goes to a connector then the second half of the connector doesn't seem to match up with the first and the "bundle" that crosses the car is broken and the other section of the bundle has the wires in a different order so you have to look at the labeling to make sure you have the 22brdblwtst and not the 22brwtst. (22 Ga. brown double white stripe not....single white stripe) Harry

I know what you mean Harry.. Those GM "generated" schematics are a nightmare. I work with consumer electronics (I'm an Amateur Radio Operator) on a daily basis and the schematics for that industry are just as bad.. You'd think by now, an electrical schematic would be just a simple roadmap.. I've always said those automotive engineers should have to spend time "on the line" as an ongoing part of their job.. One of the dumbest things to do is put a fusible link inside a wiring harness.. That's an invitation for a fire.

I don't recall the component location info being in the same book with repair procedures or the flow chart information. They (the component locator guide) were a separate publication. I still have a library of service/repair manuals, OEM, Chiltons, Motor, and a few others.. If memory serves me, Chilton was the company that offered the component locator manuals..

Starfire, when you get back to the RWD, let me know and I'll dig out my component locator books and see what they have to say about that inline fuse..

RustyPile