A little electrical help please

[Joe R.]

Re: A little electrical help please

Joe L - Yes, these switches are actually fairly easy to find (there are a few on ebay right now), but for some reason the owners think they're made out of gold, so the prices are ridiculous. I refuse to pay $200 for a stupid switch!

Joe R - I also posted a request on the Camaro site and one of the guys there said The original blue block resistors read out between approximately 4 to 6 Ohm's and are rated at 5 or 10 watts. So with that info, what would you suggest?

Ed

Hi Ed,

I would suggest still taking the voltage measurements across the resistor and the battery. I would rely on that being accurate before I would rely on someone's memory being accurate. I don't want to offend anyone, it's just that I always believe what an object is telling me over what someone tells me about the object. A 5 or 10 W resistor will be much smaller physically than a say 100 W resistor. Which is a good thing in this case!

Joe

[Edward B.]

Re: A little electrical help please

I agree. I'll get those numbers for you later on this evening Joe.

Ed

[Edward B.]

Re: A little electrical help please

Sorry Joe. Didn't have a chance to do this last night, but this morning I got the following readings while the car was running. Note that they're all approximate because all the readings fluctuated a bit. Not sure why.

Alternator output - 14.6 volts
Radio fuse (this is where the defogger gets its power from) - 14.4 volts
Switch power input - 14.3 volts
Switch high speed - 14.2 volts
Switch low speed - 10 volts

If I'm reading this right, the resistor is indeed 4 ohms (approx.) and I would imagine a 10 watt resistor would suffice? The problem is I don't know how many amps the defogger motor draws, but the radio fuse is rated at 10 amps. I can't imagine it drawing that much! I'm guessing maybe 1 or 2 amps at the most during normal operation?

Ed

[Michael H.]

Re: A little electrical help please

Well, I emailed three guys on ebay and two of them replied so far. Unfortunately, neither resistor had anything written on them so that was a dead end. However, one of the guys measured his and he said it was about 6 ohms. I measured what was left of mine and got just over 4 ohms, so I'm not sure why they're different.

So Joe, going by your equation, 16x16=256. Divide this by 4 ohms and I get 64 watts. If I divide by 6 ohms I get 42.6 watts Maybe I should get a resistor that's in the middle of the two measurements (approx. 5 ohms)? Or would you go with the 4 or 6?

Ed

Ed,

I was going to mention 100 watt 4 ohm resistor is what I would go with, Joe knows his stuff. I'm concerned with the lower wattage that you may burn something up. Radio Shack should have that in stock.

Mike

[Edward B.]

Re: A little electrical help please

So Mike, you're thinking something like THIS ONE on ebay. (Just an example. Since it's from China I doubt it's any good!)

Ed

[Rich C.]

Re: A little electrical help please

The rear defogger means of controlling fan speed must have changed over the course of 68-73, I don't know at what point they changed, but later ones use a resistance wire in the wiring harness as a means of providing a low speed. Guess that explains the 71-73 switch.

1973 LS-4 454 coupe owned 26 years
1996 LT-4 CE coupe

[Edward B.]

Re: A little electrical help please

Rich, from my research, and as far as I can tell from the documentation, the 1968 to late 1973 system was the same (a two wire switch with a resistor built in to reduce the voltage on the low side).

It changed sometime in late 1973 or early 1974 to the resistance wire you refer to, which now used the three prong switch with no resistor that you and Tom (above) mention.

The switch for 1968 was originally P/N 3861697 and changed in the AIM to 3942696. I can't make out the exact date, but it looks like ?-2-68. (The early 3861697 switch was also used from 1965 - full size and Chevelle - through 1968 - full size, Chevelle, Camaro, Nova and Corvair).

The 1969 Corvette AIM shows the part number as 3942696, and this changed ONLY for the Corvette.

(Note that the 1973 P&A 30B (dated October, 1972) shows the switch for 1969 through 1973 as the same for the late 1968, P/N 3942696.)

However, this is where it starts to get cloudy. The 1979 P&A 14 (dated 14 June, 1979) shows the 3942696 being used from 1969 to 1973 like the other P&A does, but it also shows P/N 410202 for the switch for 1974 through 1976. The problem here is that this is a plastic, 3 prong toggle switch and I KNOW there was a 3 prong "rotary" switch used in late 1973 or early 1974 because of the pictures attached.

I believe this 3 prong rotary switch isn't mentioned in any of the P&A's, but it MIGHT be mentioned in the 1973 or 1974 AIM (of which I have neither).

1st picture - Late 1973 or early 1974 3 prong ROTARY switch (front) - (No clue what the part number was)
2nd picture - Late 1973 or early 1974 3 prong ROTARY switch (rear) - (Again, no clue what the part number was)
3rd picture - Mid 1974 (?) 3 prong TOGGLE switch (front) - (Part number 410202)
4th picture - Mid 1974 (?) 3 prong TOGGLE switch (rear) - (Again, part number 410202)

Ed

[Michael H.]

Re: A little electrical help please

So Mike, you're thinking something like THIS ONE on ebay. (Just an example. Since it's from China I doubt it's any good!)

Ed

Ed,

That doesn't look right, maybe a 50-65 watt would be better. We need to get Joe R comments on this.

Mike

[Edward B.]

Re: A little electrical help please

Mike, I guess it all depends on how many amps the motor draws, right? I've no way to know that because there's nothing stamped into the motor showing that info.

Ed

[Joe R.]

Re: A little electrical help please

Sorry Joe. Didn't have a chance to do this last night, but this morning I got the following readings while the car was running. Note that they're all approximate because all the readings fluctuated a bit. Not sure why.

Alternator output - 14.6 volts
Radio fuse (this is where the defogger gets its power from) - 14.4 volts
Switch power input - 14.3 volts
Switch high speed - 14.2 volts
Switch low speed - 10 volts

If I'm reading this right, the resistor is indeed 4 ohms (approx.) and I would imagine a 10 watt resistor would suffice? The problem is I don't know how many amps the defogger motor draws, but the radio fuse is rated at 10 amps. I can't imagine it drawing that much! I'm guessing maybe 1 or 2 amps at the most during normal operation?

Ed

[Edward B.]

Re: A little electrical help please

I'm sorry I am so slow getting back to you. It was a very busy weekend.

No problem Joe. I'm in no hurry!

Are those readings with one side of the meter hooked to ground?

That's correct. I placed the positive lead of the meter on the input side of the switch and the negative lead of the meter on the negative post on the battery. (For the switch readings, I actually had to slide the connector back a little so I could access the terminals.) I got the 14.3 volts at that spot. (Again, all the voltages are approximate since the meter fluctuated a bit)

I then placed the positive lead of the meter on the HIGH output terminal and got 14.2 volts. Then, on the LOW side of the switch I got 10 volts. (It was probably more like 9.9, but like I said, they ALL fluctuated a bit)

All the readings (except for the alternator) were taken with the negative lead of the meter on the negative terminal on the battery. (The alternator was taken between the "BAT" terminal and the engine)

What I want to see is what you get if you put one lead of the meter on one lead of the resistor and the other meter lead on the other resistor lead.

If you mean taking an ohms reading of the resistor, yes, I did that and it came to 4 ohms (actually, to be more specific, 4.2 ohms). However, I DIDN'T disconnect it from the switch. I didn't want to mess with anything for fear of breaking it even more.

If you could humor me a little more, I would suggest disconnecting one lead of the resistor, put the meter in series (you will need to change how the meter leads are connected to the meter) to measure current and get high speed and low speed current readings.

I'm not sure I follow you on this one. If I'm reading you right, you want me to check how many amps are going through the resistor? If that's the case, I don't think my meter will handle that. It's only rated at 1 amp.

By the way, that 4.2 ohms may be a little off since I didn't "lift one leg" of the resistor. I made a drawing of the switch over the weekend (see attached), and I took the reading with the switch in the OFF position and the harness disconnected.

Ed

[Joe R.]

Re: A little electrical help please

No problem Joe. I'm in no hurry!



That's correct. I placed the positive lead of the meter on the input side of the switch and the negative lead of the meter on the negative post on the battery. (For the switch readings, I actually had to slide the connector back a little so I could access the terminals.) I got the 14.3 volts at that spot. (Again, all the voltages are approximate since the meter fluctuated a bit)

I then placed the positive lead of the meter on the HIGH output terminal and got 14.2 volts. Then, on the LOW side of the switch I got 10 volts. (It was probably more like 9.9, but like I said, they ALL fluctuated a bit)

All the readings (except for the alternator) were taken with the negative lead of the meter on the negative terminal on the battery. (The alternator was taken between the "BAT" terminal and the engine)



If you mean taking an ohms reading of the resistor, yes, I did that and it came to 4 ohms (actually, to be more specific, 4.2 ohms). However, I DIDN'T disconnect it from the switch. I didn't want to mess with anything for fear of breaking it even more.



I'm not sure I follow you on this one. If I'm reading you right, you want me to check how many amps are going through the resistor? If that's the case, I don't think my meter will handle that. It's only rated at 1 amp.

By the way, that 4.2 ohms may be a little off since I didn't "lift one leg" of the resistor. I made a drawing of the switch over the weekend (see attached), and I took the reading with the switch in the OFF position and the harness disconnected.

Ed

Hi Ed,

OK, I think the resistor may be dropping less voltage than your first set of readings would suggest. With the switch on low speed, please put your voltmeter leads on terminals 2 and 3 as shown in your schematic. That will tell us how much voltage the resistor is dropping. Which will tell us the wattage it needs to be and how much current the motor draws on low speed. Never mind on the ammeter suggestion.

Joe

[Edward B.]

Re: A little electrical help please

Ok Joe. And I'm assuming you want the reading with everything connected and the car running, right?

Ed

[Joe R.]

Re: A little electrical help please

Ok Joe. And I'm assuming you want the reading with everything connected and the car running, right?

Ed

Hello again Ed,

Yes, please!

Joe

[Edward B.]

Re: A little electrical help please

Ok, I'll see what I get later on this afternoon when I get off work.

Ed