Fan Blower switch has a super hot terminal

kevken1959 · Jun 22, 2024

My fan blower motor switch was going out and only working intermittently, so I decided to replace it today with what I believe to be a good used switch. When I removed the plug from the bad switch, I noticed that one of the terminals had gotten super hot and melted the black holder it was encased in. The wire and terminal had actually separated from the black holder. I replaced the switch and plugged the connector and loose wire onto it and the fan works great through all settings, but the exposed connector is still too hot to touch and I know it's just a matter of time before the switch goes out again, or worse. I really don't want to remove the dash to track down the problem. I'm thinking it's a problem with the wire going to the male terminal on the switch, and not the other way around. Can someone give me some options, like running a new lead from somewhere else to that terminal on the switch and bypassing the shorted wire (based on a wiring diagram)? Has anyone seen this problem before? I'm surprised the fuse has not blown. Here's a picture of the terminal that was fried. My finger is on the terminal. Thanks. Kevin.

72mokk1 · Jun 23, 2024

My guess is you have resistance from corrosion. As little as 2 ohms at 12 volts drawing 10 amps is like touching a 60 watt light bulb.
Judging from the color of your male connectors, and the female connectors are probably corroded also, this includes where the connector is crimped to the wire, should be very little resistance. I would clean all the connections to bright and shiny and test it again. IMHO.

kevken1959 · Jun 23, 2024

So I cleaned the male and female terminals with a wire brush, I cut the bad female terminal off and replaced it with a new one, and that terminal still gets really hot with the fan on from the key and the engine off. Any other ideas? Does anyone have a wiring diagram to tell me where this wire comes from or goes to? If it's a ground wire I could just run a new good ground wire to the male terminal. Maybe the used switch I'm using is bad too? I hate to spend $50 on a switch (plus $21.19 for shipping!!!) from Old Air Products if I don't need to (https://www.oldairproducts.com/product/24-0589-blower-switch). Maybe it is a bad blower motor resistor? Any ideas? Thanks.

Cleveland Crush · Jun 23, 2024

If you have or can borrow a DC clamp meter, I'd test that offending wire to see exactly what's going on there.

kevken1959 · Jun 23, 2024

Cleveland Crush said:
If you have or can borrow a DC clamp meter, I'd test that offending wire to see exactly what's going on there.

I've never used one but I'm willing to learn. When I Googled them about a million pop up. Can you recommend a good one for our purposes? I looked up this video: . The problem here is that I don't want to rip the dash apart and it is EXTREMELY difficult to localize these wires. They are all behind the dash and literally have no slack at all. It would seem to be impossible to get a tool that big around any of the wires without completely removing the dash or the harness from the dash. Ideas? I'm searching the forum now and finding a lot of useful information. Don C posted how to download wiring diagrams from this site and I'm at that point now. The problem with my search was that I was initially using "heater blower motor wiring diagram" and nothing good was coming up, but when I changed to just "wiring diagram" I got a lot of good links.

Cleveland Crush · Jun 23, 2024

I have an older Craftsman #82369 which are still available. Fluke also makes fine products. Key point is to get an AC/DC tester. Many being sold are AC only which obviously won't help with car trouble shooting.
I just tested my 1972's blower amp draw and this is my results on high(~6.6 amps) medium (~4.3 amps) low(~2.4amps).

Don C · Jun 23, 2024

A loose connection can also cause a resistance and overheating.
There are clamp on ammeters that are much smaller than the one you show, but will still not be all that easy to separate out the wire to measure them.
When you said that the switch works on all settings I'm assuming the blower functions at different speeds. If so, I doubt if you have a shorted wire, if you did all of the current would be going to ground (easiest path) and the resistor is also okay.
The rivet that connects the terminal to the switch may be corroded or loose, also.

Cleveland Crush · Jun 23, 2024

kevken1959 said:
I've never used one but I'm willing to learn. When I Googled them about a million pop up. Can you recommend a good one for our purposes? I looked up this video: . The problem here is that I don't want to rip the dash apart and it is EXTREMELY difficult to localize these wires. They are all behind the dash and literally have no slack at all. It would seem to be impossible to get a tool that big around any of the wires without completely removing the dash or the harness from the dash. Ideas? I'm searching the forum now and finding a lot of useful information. Don C posted how to download wiring diagrams from this site and I'm at that point now. The problem with my search was that I was initially using "heater blower motor wiring diagram" and nothing good was coming up, but when I changed to just "wiring diagram" I got a lot of good links.

You can measure the fans amp draw at the battery cable. Measure the amp draw at the battery with the ignition "On" for a benchmark reading, then turn the fan on to get your fan draw reading.

kevken1959 · Jun 23, 2024

Don C said:
A loose connection can also cause a resistance and overheating.
There are clamp on ammeters that are much smaller than the one you show, but will still not be all that easy to separate out the wire to measure them.
When you said that the switch works on all settings I'm assuming the blower functions at different speeds. If so, I doubt if you have a shorted wire, if you did all of the current would be going to ground (easiest path) and the resistor is also okay.
The rivet that connects the terminal to the switch may be corroded or loose, also.

"When you said that the switch works on all settings I'm assuming the blower functions at different speeds. If so, I doubt if you have a shorted wire, if you did all of the current would be going to ground (easiest path) and the resistor is also okay.
The rivet that connects the terminal to the switch may be corroded or loose, also."

Correct. The blower functions at different speeds. I dug out another 72 under dash wiring harness I had and found that the wire in question runs directly from the fuse box to the terminal on the fan switch that is getting hot. I also noticed that it is the largest of all the wires going from the fuse box, probably a 16 or 14 gauge. I ran a wire directly from the same fuse post to the terminal and it still gets too hot for me to keep my finger on it for more that 6 seconds. The wire doesn't get hot. Just the terminal. That is with the key on, the engine off, and the fan all the way up with the A/C clutch engaged. When I unplug the A/C clutch, the terminal is still warm but I can easily keep my finger on it indefinitely.

The rivet that connects the terminal to the switch may be corroded or loose, also."

I replaced the switch with what I believed to be a good used switch, but today when I was checking it the terminal did feel a little loose. Maybe this is a common failure point because maybe it's normal for there to be some heat at that spot considering the amount of current going through it. Maybe it's normal for the exposed terminal to be hot to the touch. The terminal is exposed now because the plastic on the plug covering it melted. I DON'T think that's normal. I'm thinking about going ahead and ordering a new switch to rule that out as a problem.

kevken1959 · Jun 23, 2024

Cleveland Crush said:
I have an older Craftsman #82369 which are still available. Fluke also makes fine products. Key point is to get an AC/DC tester. Many being sold are AC only which obviously won't help with car trouble shooting.
I just tested my 1972's blower amp draw and this is my results on high(~6.6 amps) medium (~4.3 amps) low(~2.4amps).

I wasn't able to find the Craftsman but the one the guy in the video is using one that costs $300+. https://www.zoro.com/amprobe-clamp-...DZ0X0cKf4xAA5wI8x0kaAvcQEALw_wcB&gclsrc=aw.ds

Then I see them for as cheap as $20 on Amazon: https://www.amazon.com/Auto-Ranging...a86f82e6136f35b4a5938512a5af1449&gad_source=1

What gives? It's hard to see the need to spend more money.

Cleveland Crush · Jun 23, 2024

There's some decent entry-level AC/DC meters for $50-$60 no need to spend more for hobby use. Be sure the meter measures DC amps along with AC amps and AC/DC volts along with all the other typical measurements. Many of these meters do NOT feature DC amp measurements which are very useful for automotive work!

Cleveland Crush · Jun 23, 2024

kevken1959 said:
I wasn't able to find the Craftsman but the one the guy in the video is using one that costs $300+. https://www.zoro.com/amprobe-clamp-...DZ0X0cKf4xAA5wI8x0kaAvcQEALw_wcB&gclsrc=aw.ds

Then I see them for as cheap as $20 on Amazon: https://www.amazon.com/Auto-Ranging...a86f82e6136f35b4a5938512a5af1449&gad_source=1

What gives? It's hard to see the need to spend more money.

Also Kevken the Amazon meter in your link does NOT measure DC amps (only DC volts). You don't want that particular meter!

kevken1959 · Jun 23, 2024

Thanks Chris! I bought this one. No problem if I have to return it. What do you think? https://www.amazon.com/gp/product/B0CR7GKSLC/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

Cleveland Crush · Jun 23, 2024

That meter will do the trick!

Bill Kanode · Jun 24, 2024

kevken1959 said:
"When you said that the switch works on all settings I'm assuming the blower functions at different speeds. If so, I doubt if you have a shorted wire, if you did all of the current would be going to ground (easiest path) and the resistor is also okay.
The rivet that connects the terminal to the switch may be corroded or loose, also."

Correct. The blower functions at different speeds. I dug out another 72 under dash wiring harness I had and found that the wire in question runs directly from the fuse box to the terminal on the fan switch that is getting hot. I also noticed that it is the largest of all the wires going from the fuse box, probably a 16 or 14 gauge. I ran a wire directly from the same fuse post to the terminal and it still gets too hot for me to keep my finger on it for more that 6 seconds. The wire doesn't get hot. Just the terminal. That is with the key on, the engine off, and the fan all the way up with the A/C clutch engaged. When I unplug the A/C clutch, the terminal is still warm but I can easily keep my finger on it indefinitely.

The rivet that connects the terminal to the switch may be corroded or loose, also."

I replaced the switch with what I believed to be a good used switch, but today when I was checking it the terminal did feel a little loose. Maybe this is a common failure point because maybe it's normal for there to be some heat at that spot considering the amount of current going through it. Maybe it's normal for the exposed terminal to be hot to the touch. The terminal is exposed now because the plastic on the plug covering it melted. I DON'T think that's normal. I'm thinking about going ahead and ordering a new switch to rule that out as a problem.

If you order a new switch don't forget to crimp on a new stakon to the wire otherwise the old terminal will burn the new switch. Once a stakon gets hot it loses the clamping force to adequately make a good connection. As a 40 year electrician I have seen this happen MANY times which will also melt the holder for the wires. If you do have a melted wire holder ask Randy @ Midlife wiring to see if he has one. Your local NAPA store has the #56 GM brass terminals which is common across American car manufacturers . Thx, Bill

Mark Jones · Jun 24, 2024

I would check and cleanup the fan motor ground wire. Replace the sheet metal screw and possibly crimp on a new ring terminal.

kevken1959 · Jun 24, 2024

Bill Kanode said:
If you order a new switch don't forget to crimp on a new stakon to the wire otherwise the old terminal will burn the new switch. Once a stakon gets hot it loses the clamping force to adequately make a good connection. As a 40 year electrician I have seen this happen MANY times which will also melt the holder for the wires. If you do have a melted wire holder ask Randy @ Midlife wiring to see if he has one. Your local NAPA store has the #56 GM brass terminals which is common across American car manufacturers . Thx, Bill

Thanks Bill!

kevken1959 · Jun 24, 2024

Mark Jones said:
I would check and cleanup the fan motor ground wire. Replace the sheet metal screw and possibly crimp on a new ring terminal.

Will do. Thx!

kevken1959 · Jun 24, 2024

Bill Kanode said:
If you order a new switch don't forget to crimp on a new stakon to the wire otherwise the old terminal will burn the new switch. Once a stakon gets hot it loses the clamping force to adequately make a good connection. As a 40 year electrician I have seen this happen MANY times which will also melt the holder for the wires. If you do have a melted wire holder ask Randy @ Midlife wiring to see if he has one. Your local NAPA store has the #56 GM brass terminals which is common across American car manufacturers . Thx, Bill

What's the best tool to crimp the new connector on, and what's the best tool to get the connectors out of the holder?

Fan Blower switch has a super hot terminal

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