Did you do the upgrade for the heater blower? The blower is case grounded through the mounting screws

 

In my YJ Wrangler , the heater blower is also grounded through the mounting bolts on the passenger firewall as OEM setup.

My issue is for a separate A/C fan which in my YJ is located closer to the driver knee area.
This A/C fan sporadically was dropping the ground via black wire screwed into a bezel screw at the driver left knee.

I experienced that when I held the rusty tip of the wire near a chassis ground with the A/C blower " on ", the rusty wire end got too hot to hold. I attributed the resistance from the rust as the dropping ground issue.
Question : Where is OEM grounding location for the A/C fan black wire ?

 

Sorry about that. It really shouldn't matter where you ground it. The dieelctric grease was a good move but if your getting that much rust that quick then there is something else going on. The sanding actually set you up to have rust. Untreated metal exposed to air and water will rust. Use a stainless screw or a zinc screw so you dont have the issue with dissimilar metals.

 

Just ground it to any clean metal spot on the dash. You can ground it to the firewall if you want. The A/C system was a dealer option on the older YJ's and was installed by the dealer. Most times they just have it going to one of the screws that hold the a/c to the bottom edge of the dash.

 

Who's bringing up a 10 year old thread...this guy!

I am bringing it up because I'm curious about my A/C and heater blower motor grounds. When I turn on the A/C or heater, my voltage gauge drops significantly for anything over the middle speed. If it's on "HI" it's probably near 10V on the gauge.

One thing I did in the past was wire in a separate fuse holder from the fuse panel. The stock fuse holder had overheated and was loose from it. One thing I do know is the heater motor and A/C blower ran through the same fuse, a 25A in the stock fuse holder. If the heater blower motor is mounted to the firewall, I can run a dedicated wire to it but I'm not sure about the A/C blower motor. I was curious if one of the gurus knew.

 

What you describe Louie is not necessarily a ground issue. My 87 has some voltage gauge issues at times but I know for sure that there has been a good amount of water behind the dash over the years and even in a perfect world, all the copper connections in the vehicle can and will oxidize over time.

You can pop your voltage gauge out and figure out which terminal is supposed to be battery voltage. Connect one probe of a voltmeter to that terminal and the other probe of the voltmeter to the POSITIVE battery cable. Yes, both probes of the meter are hooked to positive. When you operate the system any voltage that is measured on the voltmeter is called a voltage drop. You are dynamically finding the loss in the circuit that can be caused by bad connections, wires, etc.... It measures any unwanted resistance. If you get a reading of more than .2v to .5v you have unwanted resistance in the circuit.

As far as a blower motor ground. The same test works. Probe the ground at the blower ground wire and the other probe at the battery negative terminal. Operate the circuit. If it reads more than .2v to .5v is has unwanted resistance. You can further isolate it by checking from the blower to the tub metal, from the tub to the engine, from the tub to the battery, from the engine to the battery, etc. When you find the segment of the circuit that gives you the higher reading, you found your problem.

Resistance and continuity testing or purely checking for voltage at a component with a meter or a test light does not always work because the system is not dynamically loaded. I will use a very extreme example. You have a starter that will not crank the engine. Battery tests at 12.6V. Test the battery cable at the starter and get 12.6V or a test light that lights. Test the positive cable with an ohmmeter and get close to 0 Ohms. Continuity tester works also. If my battery cable broke all but a couple of strands of copper I can still get 12V at the starter or a test light that lights and an ohmmeter only needs that couple of strands of copper to give me 0 ohms. If I connected a voltmeter to measure the actual voltage drop in the circuit, thus one probe to the positive post of the battery and the other to the positive post of the starter and tried to crank the engine over I would have a very high reading on my voltmeter, like close to battery voltage in this situation. Why. Because the two strands of copper cannot handle the current that it needs to operate. The meter is reading the loss of voltage in the circuit when wired this way.

A voltmeter reads a difference in voltage potential. It is not just a power and ground reading device. Understanding a voltage drop test is a super powerful diagnostic method that isolates stuff quickly and easily. I reiterate that it works on ground circuits also.

 

Thank you, good sir. I probably should have sat down and thought about it more instead of a knee jerk reaction and posting to JF.

My thought is once the load is put on the circuit all the added resistance in the old wires has built up thus resulting in a voltage drop that in turn ramps up your current. Thankfully, Ohms law prevails and I can use your method to diagnose. I usually go to grounding first since it’s really easy to diagnose and overlook.

Similarly, I went through this with my head lights. I was getting 10V at the lights and wired directly to the battery with properly rated continuous duty relays. Made a world of difference. I think I can make my blowers work better if i rewire them.


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Thank you, good sir. I probably should have sat down and thought about it more instead of a knee jerk reaction and posting to JF.

My thought is once the load is put on the circuit all the added resistance in the old wires has built up thus resulting in a voltage drop that in turn ramps up your current. Thankfully, Ohms law prevails and I can use your method to diagnose. I usually go to grounding first since it's really easy to diagnose and overlook.

Similarly, I went through this with my head lights. I was getting 10V at the lights and wired directly to the battery with properly rated continuous duty relays. Made a world of difference. I think I can make my blowers work better if i rewire them.

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You are very welcome.

Your response opened a can of worms because in a typical lighting circuit for instance the voltage drop or increased resistance limits current flow or ramps it down. Thus the poor performance in the circuit. With that being said and where the confusion begins, motor circuits are different as in starter motors where increased resistance can make starter draw and amperage increase dramatically if measured at the voltage source.

If you get and understand a voltage drop you can use it to find a bad connection. Say you have a corroded battery terminal to cable clamp connection on a top post battery. If you measure the entire circuit as in battery to starter post and see .2v, leave the circuit alone, it is good. If you see a big drop, start isolating it in segments. Check post to terminal and get a larger than acceptable drop, address that segment of the circuit. Rinse and repeat throughout the circuit. You can back probe a connector from both sides to check it. You may have good and clean connectors but a poor pin fit and tension in the connector. This test will nail it dynamically. With a good min max meter it can find intermittent connections. JS,

 

Good info. I always enjoy electrical talk for automotive stuff because I learn quite a bit from
others on the forum who know way more than me.

By the way, I’m an electrical substation engineer. But don’t be fooled, I’m not a EE by any means. I’m more of an ME who pretends to know electrical stuff.


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Good info. I always enjoy electrical talk for automotive stuff because I learn quite a bit from
others on the forum who know way more than me.

By the way, I'm an electrical substation engineer. But don't be fooled, I'm not a EE by any means. I'm more of an ME who pretends to know electrical stuff.

Sent from my iPhone using Tapatalk

Rock on!

I am a career auto mechanic of 40 years experience with a college and many different auto manufacturers education in diagnostics and theory. I like to build tube guitar amps and stuff as a hobby. I get this stuff and electrical is possibly my favorite thing of the car. Very time consuming though, especially on the net.

PM me at any time for help.