Troubleshooting cooling fan

[DMC-Ron]

I was installing Dave's electronic fan relay when I noticed my front left fan (original fans still in car) was not running. Nothing to do with the new electronic relay (which works great). So I did some troubleshooting:

1. Unplugged the left fan and connected it to a portable 12 VDC source - fan runs just fine.
2. Measured the voltage at the plug supplying current to the fan (with fan disconnected - multi-meter probes in plug). Indicated 6.8 volts.
3. Measured the voltage from the positive plug prong to frame ground of car. Same, 6.8 volts.
4. Measured ohms resistance from negative prong to frame. Low, around 0.3 ohms.
5. Measured voltage leaving the fan fail socket (I still have fused jumpers in socket) with negative lead referenced to negative battery post. 12.5 volts.

A little perplexed about the voltage drop. How could I get 6.8 volts at the fan connector with just the multi meter plugged in (essentially no load)? The right fan is working normally. Ran out of time (how's that possible with a DeLorean?) and had to put this aside for later. Perhaps someone has a tip on this.

Thanks,
Ron

[Bitsyncmaster]

Yes that is very strange to see a voltage drop without a load connected. Are you sure your meter did not auto range to another scale so you did not really see 6.8 volts?

[Ron]

5. Measured voltage leaving the fan fail socket (I still have fused jumpers in socket) with negative lead referenced to negative battery post. 12.5 volts.

Did you check it at the socket's terminal itself (v/s the terminal that plugs into it from the fused jumper)?

I'd try connecting everything up then swapping the two fused jumper terminals....
Or, bypassing the socket's terminal by applying 12V to the BG wire immediately after it...

[Bitsyncmaster]

Most fuses you can touch a pointed meter probe on the little metal tabs on the top of the fuse to measure the voltage under load.

[DMC-Ron]

Ron and Dave,
Good suggestions. It occurred to me that the connector in the fan relay socket might have backed out. I felt underneath and there didn't seem to be anything pushed back. From the top it looks fine. I'll check it again then measure it under load. I'm also going to extend a wire to the battery ground lug so I can see actual plus voltage at the fan plug. Later, I can switch and use the same wire for the + voltage and tap from the relay socket to the fan.

The multi-meter is new to me (I purchased one with dwell) but it is not auto-scale, so I think the 6.8 volt reading was valid. I'll verify with my fluke.

Later,
Ron

[Bitsyncmaster]

Ron and Dave,
Good suggestions. It occurred to me that the connector in the fan relay socket might have backed out. I felt underneath and there didn't seem to be anything pushed back. From the top it looks fine. I'll check it again then measure it under load. I'm also going to extend a wire to the battery ground lug so I can see actual plus voltage at the fan plug. Later, I can switch and use the same wire for the + voltage and tap from the relay socket to the fan.

The multi-meter is new to me (I purchased one with dwell) but it is not auto-scale, so I think the 6.8 volt reading was valid. I'll verify with my fluke.

Later,
Ron

I have used a long meter jumper wire to find voltage drops for my fuel pump. It's a great way to get the ground reference clipped right on the battery terminal so you can find voltage drops with one solid reference point.

[DMC-Ron]

A little further troubleshooting on this issue and I have found that I have 22K ohm resistance in the wiring from the fan fail relay socket to the + side of the fan connector.

But let me back up a bit. Previously I found that if I injected +12 volts into the fan connector the fan would run. This verified the fan ground was fine (I thought for sure it was probably a grounding issue). Here is the probe supplying +12 to the fan (nothing disconnected at this point):
PA272325.jpg

If I connect my meter at the fan fail relay and the disconnected fan plug for a continuity test I see the 22K ohms of resistance:
PB202319.jpg PB202326.jpg

So my questions: Would it seem likely that the resistance is a poor connection? What would be the most likely cause and location for this issue (bad connection??)? This is the left cooling fan green/black wire between the fan fail relay and the left cooling fan connector. When I look at the wiring schematic, I see connector designations shown but it's not clear if the represented connectors are in the wiring harness or if the connector shown in the circuit represents the connector right at the cooling fan. More to the point, are there any connectors in the wiring harness I should focus on?
Cooling Fan Wire Schematic.JPG

I would appreciate your suggestions,
Ron