Voltmeter reading
Nordschleife Master
Joined: May 2005
Posts: 7,326
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It's important to get to the back of the alternator because if the starter y-cable is bad, the voltage will be lower at the engine bay positive lug.
Please see the j hook tool I made to probe the back of the alternator here.
Please see the j hook tool I made to probe the back of the alternator here.
Thread Starter
Rennlist Member
Joined: Oct 2015
Posts: 1,145
Likes: 205
From: Prescott, AZ
I did make that hook to reach the back of the alternator. The instructions describe testing between the alternator back to the battery terminals (B+ and B-) so it sounds like I also need wires to run to the battery, or can I take those readings using the engine bay positive lug and the chassis as the ground?
I did take just readings at both the battery (B+ to B-) and at the engine bay positive lug to chassis (lug at air cleaner mount) with the engine off and got the same reading (12.64v at both locations). With the engine on I got 12.53v at the battery and 12.64 at the engine bay positive terminal/chassis..
I did take just readings at both the battery (B+ to B-) and at the engine bay positive lug to chassis (lug at air cleaner mount) with the engine off and got the same reading (12.64v at both locations). With the engine on I got 12.53v at the battery and 12.64 at the engine bay positive terminal/chassis..
Nordschleife Master
Joined: May 2005
Posts: 7,326
Likes: 77
If you perform tests 1-5, you should be able to id the culprit. It's important to follow the steps as written in the instruction.
If you suspect the alternator, one quick test (test #5) is measure the voltage between the back of the alternator (using the hook) and the alternator case. When the engine is running (at idle) and with some load like low beam and a/c ON, the alternator should output at least 13.5v
If you suspect the alternator, one quick test (test #5) is measure the voltage between the back of the alternator (using the hook) and the alternator case. When the engine is running (at idle) and with some load like low beam and a/c ON, the alternator should output at least 13.5v
Nordschleife Master
Joined: May 2005
Posts: 7,326
Likes: 77
I did make that hook to reach the back of the alternator. The instructions describe testing between the alternator back to the battery terminals (B+ and B-) so it sounds like I also need wires to run to the battery, or can I take those readings using the engine bay positive lug and the chassis as the ground?
I did take just readings at both the battery (B+ to B-) and at the engine bay positive lug to chassis (lug at air cleaner mount) with the engine off and got the same reading (12.64v at both locations). With the engine on I got 12.53v at the battery and 12.64 at the engine bay positive terminal/chassis..
I did take just readings at both the battery (B+ to B-) and at the engine bay positive lug to chassis (lug at air cleaner mount) with the engine off and got the same reading (12.64v at both locations). With the engine on I got 12.53v at the battery and 12.64 at the engine bay positive terminal/chassis..
Thread Starter
Rennlist Member
Joined: Oct 2015
Posts: 1,145
Likes: 205
From: Prescott, AZ
I was able to get a reading on test #5. Was able to get a pretty stable reading around 13.65v and when i would lift the ground the readings went to random, replacing the ground the meter went back to 13.65. Repeated this several times for confirmation. So it doesn't look like the alternator is a fault. More like one of the cables so I'll test for that, esp #3 for the Y-cable. I guess that's good new about the alternator. I suspect this is the original Y-cable.
Nordschleife Master
Joined: May 2005
Posts: 7,326
Likes: 77
I was able to get a reading on test #5. Was able to get a pretty stable reading around 13.65v and when i would lift the ground the readings went to random, replacing the ground the meter went back to 13.65. Repeated this several times for confirmation. So it doesn't look like the alternator is a fault. More like one of the cables so I'll test for that, esp #3 for the Y-cable. I guess that's good new about the alternator. I suspect this is the original Y-cable.
Thread Starter
Rennlist Member
Joined: Oct 2015
Posts: 1,145
Likes: 205
From: Prescott, AZ
I thought an update on this problem might be useful to someone else.
It looked like the problem was likely caused by the "y" cable so i bought one. Got it ready to install (removed the "box" on the end so i could work the cable into place without removing the A/C). Got ready to start work and ran into a time crunch with an upcoming trip. So I decided just to wait until winter when i would be installing the M030 suspension to tackle this at the same time. So the gods of procrastination got me. I had to drive down to Phoenix (about 2 hrs away ) to visit Evoms for a mod to my air intake system. When they went to pull the car into the shop the battery was flat dead. Further testing pointed to the alternator so they installed a Bosch re-build. Had them install the new "y" cable at the same time. The old cable was definitely corroded but not completely shot. Between the two new parts, the car now starts easily and the voltmeter on the dash now reads around 14v when it is started up. I suspect it was the alternator that was the culprit all along but the "y" cable certainly was due for replacement.
Big take-away, don't procrastinate........
It looked like the problem was likely caused by the "y" cable so i bought one. Got it ready to install (removed the "box" on the end so i could work the cable into place without removing the A/C). Got ready to start work and ran into a time crunch with an upcoming trip. So I decided just to wait until winter when i would be installing the M030 suspension to tackle this at the same time. So the gods of procrastination got me. I had to drive down to Phoenix (about 2 hrs away ) to visit Evoms for a mod to my air intake system. When they went to pull the car into the shop the battery was flat dead. Further testing pointed to the alternator so they installed a Bosch re-build. Had them install the new "y" cable at the same time. The old cable was definitely corroded but not completely shot. Between the two new parts, the car now starts easily and the voltmeter on the dash now reads around 14v when it is started up. I suspect it was the alternator that was the culprit all along but the "y" cable certainly was due for replacement.
Big take-away, don't procrastinate........
