89-91 Voltage "pulsing" issue solved!

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89-91 Voltage "pulsing" issue solved!

Postby CumminsPower59 » Wed May 07, 2014 10:16 am

Like many of you guys with NON-IC trucks, my 91 had the voltage "pulse" when running. It was really noticeable at night at idle, as the headlights would slightly dim about two to three times a second. This condition is caused by the voltage regulator (V/R), but, not because it is faulty. The key on circuit that the V/R gets its input voltage from, has a slight drop in it, so when it senses the lower voltage it tells the alternator to charge. It charges till it reaches the correct voltage, then drops off. This condition will occur several times a second. Well, I was tired of it and wanted to finally do something about it. I had already cleaned all the grounds, added a separate ground from the alternator case to the block, and upgraded to the "Blue V/R". I spent a little time looking at the FSM and this is what I came up with.

This is the final result. Don't pay any attention to my use of shrink type connectors, as my micro torch ran out of gas when I went to use it :?
Image

And here is how we get there!

First, remove the V/R from it's original location. This is the plug you will cut from the harness.

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Here are the wires with the tape cut off. You need about two plus inches of wires off the V/R connector. The blue wire is key on and this is where the V/R gets its feed from, where it reads the system voltage.

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I like to cap off the unused wires, just so I know in the future that it isn't being used. I have a bad case of CRS (can't remember sh!t) ;)

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I used some blue 14 gauge wire I had, so I could keep the correct colors that were used originally. Use whatever you want or what will work. Run it inside the split loom down to where the ALT A/C connector is.

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Next, take a look at the wiring on the connector down by the ALT. You'll see two small blue 16/18 gauge wires, one blue 12/14 gauge wire, and the other end of the small green wire that was capped at the original V/R location. This picture is on the ALT side of the connector, but use I used the other side as the wire on the truck harness side felt like it was in better condition, as the ALT side felt like it was made of the same stuff as the fusible links.

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Cut the large blue wire and the small green wire about two plus inches from the connector. Cap the blue wire, as this one won't be used. Make a 12 inch run of wire and connect it to the green wire. I used green here also to keep with the original colors. Connect the other end of it to the V/R plug.


Next, get yourself a relay. I had one of these so I used it.

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Make two leads for the ground, one short one to a ring terminal, and the other will go to a chassis ground or battery. The switched power will come directly from the battery, instead of through the key on circuit. Make another 12" or so lead, connect it to the blue wire on the V/R plug and hook it to the switched terminal on the relay, and make another blue lead and connect it to the blue wire on the ALT A/C connector. Take the blue wire that was connected at the original V/R location and connect it at the trigger location on the relay.

Install it all, clean the paint off one of the sides if the V/R, and hook the ring terminal up there, just so the V/R case is grounded.

This is the finished product.

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No more wiggle wiggle of the voltage gauge and no more pulsing of the lights. Works very well. I am going to go back and heat shrink everything and clean it all up proper.
Last edited by CumminsPower59 on Thu May 08, 2014 11:50 am, edited 1 time in total.
Ike

91 W350 SRW, 3.07's, NV4500, 370's, THD LPPP, Super HX40, 2nd gen IC swap, BHAF, Isspro's, 2" lift, 285's on 3rd gen 17"'s.
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Re: 89-91 Voltage "pulsing" issue solved!

Postby RumbleFish » Wed May 07, 2014 12:22 pm

Nice! Now how do i fix this issue on my 93?
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Re: 89-91 Voltage "pulsing" issue solved!

Postby Tacoclaw » Wed May 07, 2014 1:11 pm

Same way. Intercept those wires on their way to the PCM and put in an external regulator like that and it'll be the same setup.
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Re: 89-91 Voltage "pulsing" issue solved!

Postby cmann250 » Wed May 07, 2014 1:40 pm

Awesome work Ike! I'd be doing this right now, but my factory set up has performed as it should for 2+ years. I'm too scared to change anything! :lol:
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Re: 89-91 Voltage "pulsing" issue solved!

Postby BC847 » Wed May 07, 2014 2:08 pm

Added to the "Sticky" :cool:
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Re: 89-91 Voltage "pulsing" issue solved!

Postby CumminsPower59 » Wed May 07, 2014 3:12 pm

BC847 wrote:Added to the "Sticky" :cool:


Thank You Sir!!! :mrgreen:
Ike

91 W350 SRW, 3.07's, NV4500, 370's, THD LPPP, Super HX40, 2nd gen IC swap, BHAF, Isspro's, 2" lift, 285's on 3rd gen 17"'s.
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Re: 89-91 Voltage "pulsing" issue solved!

Postby jdiesel_us » Thu May 29, 2014 12:58 pm

Awesome my truck has this issue and I just happen to have a similar relay in my tool box.
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