Eastflorida

1972 Cutlass...

OK, electrical is not my strong point, so I could use some advice and suggestions.

The 4 AMP instrument lights fuse continues to blow (dash lights and console shift light). Originally I thought it was bad bulbs, but the fuse blows shortly after the lights are turned on.

Any suggestions on where to start trying to find the problem?

Thanks!

oldcutlass

Your going to have inspect the wiring and find the short. All the lights are gray wires.

Eastflorida

Just noticed this... The intensity works to turn the cab light on/off. Just noticed the right turn signal on the dash is lit when the lights are on.. Must be a bad ground somewhere! Any ideas where to look?

oldcutlass

Yes the headlight switch works the courtesy lights if turned all the way to the left. The directional light gets its power directly from the turn switch and may be a separate issue. Your issue is not a bad ground, its a short in IP lighting, gray wire to ground. Have you been fiddling behind the dash or in the console?

Eastflorida

Yes, installed new dash speaker, stereo, gauges (accessory oil, volt, water), replaced dash lights... been messing in there quite a bit, but the blown fuse was an issue before all that...

oldcutlass

Again your going to have start looking at all the gray wires. If you turn on the lights, does your turn signal light go on and off with the high beam switch? What happens when you operate the turn signals do both indicators on the dash work?

Eastflorida

Well, My initial test to answer your questions didn't go well. The side markers were blinking on the right side, but the front one stayed lit. After cycling through the high beam a few times, everything started to work properly. The dash right signal marker also went off.

Good right? So I put my last fuse in and had dash lights too! Only for a minute though... Once I turned the lights off then back on, the fuse blew again...

oldcutlass

Have you tied anything thats got a big load to the dash light circuit?

Eastflorida

Since I can't find a reason why the dash lights fuse keeps blowing, I'm trying to replace the headlight switch.

I push in on the button to release the ****/shaft, but it won't come out.

Any suggestions?

oldcutlass

Some are difficult. I don't think thats your issue.

joe_padavano

Yeah, here's a suggestion. Learn to read the wiring diagram. Once you do, you will see that the fuse that keeps blowing is DOWNSTREAM of the headlight switch. There is NO POSSIBLE failure of the headlight switch that can cause that fuse to blow. Feel free to keep throwing time and money at problems or learn to diagnose a problem BEFORE spending time and money. Your call.

The only way for that fuse to blow is that there is a short somewhere in the grey wire inst light circuit, period. There is no other possible cause. Find the short. This is a painful brute force problem to fix.

Eastflorida

Thanks Joe, I do need to learn how to read the wiring schematic...

budg

Yeah wiring problems can be frustrating for sure. Joes right though, if you learn to read a schematic it makes it so much easier. If you havent already ,learn to get proficient with a volt ohmeter too. They both go hand in hand. The schematic will help you isolate the circuit , the VOM will help you track it down. The safest thing to do is work with the power off if you can .

joe_padavano

The problem with newer electronic VOMs is that they are low impedance - they put very little load on the circuit being tested. That means that a loose or high resistance connection can show "good" with the VOM but still won't flow enough current to operate the circuit. In cases like this, you need a high-impedance VOM or a good old fashioned test light.

oldcutlass

If the fuse didn't blow until the switch was cycled, I think something in the circuit was added and is overloading the fuse.

joe_padavano

The fuse doesn't get power until the headlight switch is turned on, so of course it won't blow until the headlight switch is on.. The tail light fuse feeds the park/tail light circuit in the headlight switch. This feed is split inside the switch and also feeds the rheostat that dims the instrument panel lamps. This variable voltage exits the headlight switch on a green wire and feeds the 4A INST LAMPS fuse in the fuse box. A grey wire runs from this fuse to all the illumination lamps in the car - instrument lamps, ash tray, console illumination, heater control lamp, and clock lamp. Since this 4A fuse is adequate to power all the standard and optional illumination bulbs in the car, it would take a substantial load to overpower it. A short is far more likely.

oldcutlass

He stated above that the dash lights were on for a minute and then he cycled the switch., so I was thinking a load problem instead of a direct short.

joe_padavano

Obviously, any non-stock wiring needs to be looked at. Since the OP hasn't provided that info, it's just speculation at this point.

budg

Very true . 4 amps isn't a lot. If anything was added to that circuit it would certainly cause the fuse to blow. If he has an amp probe maybe seeing what the current draw is before anything is energized. Then turning lights on. If it's just drawing too much current it will be apparent. Otherwise look for a short.

joe_padavano

4A is plenty for illumination - which is what it is supposed to be for. Even adding aftermarket gauge illumination bulbs to this circuit won't overload it - done it many times. And until the headlight switch is turned on, there is no current flowing in this circuit, so your meter will show nothing.

Look, this is not hard. First, IF there has been anything added to the circuit (and we STILL don't know that) disconnect it. Second, disconnect every load on the circuit and see if the fuse blows. If not, reconnect them one at a time until it does blow. That's where the problem is. No special test tools or probes required. Why do people need to make electrical problems so complicated?

Eastflorida

I don't see anything added to the circuit... Forgive me guys as I'm an electrical idiot!

I'm not blowing a fuse with the tach removed, everything works and the fuse doesn't blow. When I reinstall the tach, the fuse blows.

I have a gray, orange and green going to the tach.

The green is spliced and goes to the right stud (looking from the back of the instrument, the orange goes to the left stud and the gray has a connector. Nothing is attached the the top stud. Could the clock being INOP be a contributor? The schematic I have doesn't show the tach...

Joe, go ahead and yell at me again...

joe_padavano

NOW we're getting somewhere.

Gray should be illumination, orange is power for clock and tach, and green is the tach signal wire from the coil.

That is correct.

Unlikely.

Chapter 15 Accessories in your CSM.

The gray wire coming from the back of the case is SUPPOSED to be insulated from the case and is the illumination feed into the tach. If that lead is internally shorted, that will cause the fuse to blow. Try one thing. Remove the two sockets with the bulbs. Reconnect the tach and illumination lead and see if the fuse blows now. If it still does, there is an internal short in the tach. If not, one of the sockets for the 194 bulbs is bad.

Eastflorida

SUPPOSED to be INSULATED from the case... The insulated wire had rubbed against the tach and that was my short... EVERYTHING works now, not even blowing the 2 AMP fuse I put in for testing...

Thanks to Joe and all the others for your tips and insights!

joe_padavano

Congrats. THIS is why you want to diagnose and troubleshoot BEFORE buying any parts.

Eastflorida

You're right, but I bet you haven't seen this short before!! LOL

joe_padavano

Nope, but I've seen similar ones. The worst was a short on the (unused) feed for the underhood light on my first 68 442. The pigtail would bounce around and only occasionally short out and blow the fuse. Intermittents like that are the worst!

oldcutlass

Good job in troubleshooting your issue. Its hard for us sometimes to give a direction on electrical issues because we can't see what you have and can only go by what you tell us.