Problem with Instruments - New Alternator

Mike · **Joined:** 09 Jul 2008 12:51 **Posts:** 251

I just installed a new Wilson alternator; a replacement for the Motorola Prestolite alternator. The old alternator had a wire soldiered to one of the stators? I used the old voltage regulator for the new alternator. The tach did not work so I soldiered a wire at the same place as the old one, this caused the tach to work. However I have a huge problem now with all of my gauges after running a bit and increasing rpms. The instruments bounce wildly; oil pressure seems high and temp gauge is showing on the high side. I took a 7 hour trip recently and when noticing the temp go high I started monitoring the temp with my laser temp gun; shooting the thermostat area. I did this every 30 minutes for the entire time. Each time the temp gun showed normal ranges 180-184 degrees. As soon as I got to my destination and reduced rpms all gauges started to act more normal.

I'm thinking the voltage regulator is shot. Anyone experience the same ?

sord · **Posted:** 08 Jul 2013 07:08

Not with the addition of anything new but my Tach has always bounces around.

jvoelxen · **Joined:** 21 Oct 2006 15:36 **Posts:** 268

It's really hard to provide any advice without knowing more information. I'm assuming you originally had an external voltage regulator. Make sure the new alternator does not have a built in regulator. If it doesn't the original alternator was wired as follows: 1). the regulator red lead should go to the REG terminal; 2). the regulator green lead should go to the FLD (field) terminal; 3). the regulator black lead should go to the GND (ground) terminal; 4). the tachometer lead should attach to the TACH or AC terminal 5.) a ground lead from the battery should be attached to the GND terminal, and 6). the output lead (large RED lead) should be attached to the output terminal. If the alternator has a suppression kit (i.e., a capacitor ) the body should be grounded and the lead from the capacitor should be connected to the output terminal. Now, if you have a newer voltage regulator, it will be wired slightly differently (I have a Balmer unit), but you need their wiring instructions to get it right.

Hope this helps a little.

Velera · **Joined:** 29 Dec 2006 09:38 **Posts:** 656

I always take my new alternators to a pro for the rewiring for external regulation. I have rebuilt and replaced diesels, reglassed my hull, but I do not trust my soldering and wiring inside an alternator. Easy to screw up. My thought is that you do not have the new stator wired correctly around your internal regulator.

Mike · **Joined:** 09 Jul 2008 12:51 **Posts:** 251

I contacted the tech support at Wilson Electronics that made the alternator. After telling him the symptoms he told me several things that might be wrong then I remembered that the ground terminal on the alternator was not as tight when I hooked things up; the terminal itself had a loose backing bolt. He said if it works ok on low RPMs and then starts going crazy at higher RPMs and the ground is loose it can cause large spikes in the voltage causing the exact symptoms that I was seeing. He advised running a ground wire from that terminal to the mounting bracket of the alternator and went on to say that he advises this on new installations just to be sure that a good ground exists. This problem had started showing up at lower rpms just the day before. I followed his advice yesterday and my instruments ran steady with no jerky or wild motions; haven't gone out yet and tested the fix at high rpms yet but it seemed to be like night and day when I installed the ground wire.

Mike · **Joined:** 09 Jul 2008 12:51 **Posts:** 251

Verified today with a test run that the instruments were bouncing wildly due to a poor ground wire on the alternator. I installed an additional ground wire and it took car of the problem.

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Problem with Instruments - New Alternator

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