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1991 K5 Electrical

Old 11-22-2009, 02:00 PM
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I am trying to verify something I found when my alternator died abruptly this past week. When I went to remove the current alternator I noticed that the "plug-in" lead to the alternator (has a black clip with a brown wire and a brown or orangish wire with a white stripe and a little white cylinder inline) had been spliced before. I found that the brown/orange w/white stripe had been reconnected to the solid brown and vice versa. I undid this thinking someone wasn't paying attention and put it back the way it logically seemed it should have been. Now I am noticing that some of my gauges are questionable. The voltage gauge seems to read fine now reading around 14V. The oil pressure gauge stays pegged most of the time (checked and oil level is correct!). The fuel gauge seems to be much slower to head towards empty now as compared to before when a 60mile trip would make a pretty good difference (full to 3/4 reading) where as now it seems to stay FULL most of the time with the occasional fall to true level and then back to full. Then this morning on the way home it started running a little rougher than usual and everyonce in a while the red battery indicator would flash and the volt meter would drop below 13 and then go back to normal.

First question is what is the pair of wires on the alternator that are an actual plug for? I can't find diagram 1 anywhere online and the manuals i have don't break it down that far.

Second question is would there have been a reason for these two wires to have been cut and then re-spliced together backwards?

Frustrated... just seems that when I corrected the seemingly backwards wires problems started. Trying to understand the wiring before going back. Also don't want to burn up more alternators.

A good link or a good reference to a manual that would really break down the underhood or full truck electrical would be great.

Thanks again guys. -Andy

Just thinking... I assumed that the alternator had an internal regulator... any chance that this truck has an external regulator under the hood somewhere that may be toasty?

OK. I stated the wrong colors earlier:

There are 4 wires total going to the alternator:

Connected to the BAT terminal: RED/Black Stripe going to the battery. Orangish with a white cylinder (looks like a fuse block but it's solid) going back to the rear of the eng compartment into a large bundler of wires.

2 Wire connector connecting to alternator: PINK w/BLACK stripe wire and a BROWN wire. These were the 2 wires that had been cut and re-spliced back together reversed that I was questioning.

Last edited by swartlkk; 11-22-2009 at 03:24 PM. Reason: Combining Consecutive Posts. Please use the EDIT feature to add additional information to your post. Consecutive Posting is prohibitted.
Old 11-22-2009, 07:38 PM
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I know on the older setups there is an alternator charge wire which is what tells the alternator the system voltage and triggers it to charge.

On these trucks, there are two fusible links down at the starter solenoid. They look like normal wire, with a plastic capping about 1-1/2" long over them. One has "16" on it and the other "14". The number corresponds to their link rating. If these fusible links are not communicating the system voltage to the alternator, it won't charge.

I am not sure as to the wiring because my references do not like your year for some reason and older years do not show the alternator with more than 2 contacts.
Old 11-25-2009, 08:40 AM
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The brown wire goes to your gauges and then turns into a pink or blue wire which runs into your fuse box

The red wire runs into TWO fusible links, as described in the above post. There should be a junction box in between the two fusible links, should be located on the firewall. First check your fusible links... they're making contact but it may not be good contact. Also check your junction box and make sure it's clean and not corroded (wire brush & wd-40 if it is). Check that you have a GOOD ground! Obviously someone monkeyed with the wiring already and a lot of people overlook grounding. There's not a lot to a charging system so it should be easy to figure out.

Doesn't sound like you have an external voltage regulator though. Could be a smaller sized alternator that may not be putting out enough charge, that's always possible.

Easiest thing to do if you're unsure of what you have is just take it out and go to an Advance auto or somewhere they test them. They'll do the test and while you're there let them pull a replacement for your truck and see if they compare.

Hope that helped somewhat
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