Electrical Help Please!!!

[AK-5GUY]

I have an 87 K5 with a 350 TBI, which I am about to buy a new engine for since mine has a bad rod bearing. But anyways, I need a little bit of electrical help. I purchased the truck about a month ago and I noticed the system wasnt charging. I really didnt think much of it at the time, but I recently tried working on it and had no success. So far I have taken the alternator off and had it tested at autozone where it held about 14.5 volts. So I know this isnt the problem. Someone suggested that it may have been a fusable link coming off of the starter that might have blow when I jump started the truck. So I tested both of them out and found that they are both in perfect condition. Next I thought maybe its a blow fuse. So I checked all of the fuses and found all of them to be in perfect condidtion. The radio works, so does the heater, headlights, cab and dash lights, power locks, and most other things. But none of the power windows work, and the voltmeter in the truck is just laying dead under 8. This is really perplexing to me. Any help would be greatly appreciated. Thanks a ton. Harrison

 

[Michael]

There are fusible links on the starter and on the junction block on the firewall. My guess would be one of the two on the firewall junction block. Ckeck them with a continuity meter, not just viusal.

 

[95 Silverado]

borrow a voltmeter or have your complete system tested at auto-zone. If testing it yourself, hook the voltmeter leads to the two battery terminals, not running it should read around 11-12 volts, start the truck, it should increase to 13-14 volts, if it does the charging system may be working, maybe the voltmeter in the dash isn't working.

 

[dyeager535]

The alternators in our trucks are extremely sensitive to engine RPM and load. If you've got the headlights on and heater on high, idling, you will more than likely end up with barely over 12v, yet when you hit cruise, you are back up to 13+.

You can test system voltage at the fuse panel, and you can test at the back of the alternator to find out what its REALLY putting out. (you may see .5v drop between alt and fuse panel FWIW) Again, at idle, under load, anything over 12v is normal, and anything over about 13v is normal above say 1000RPM.

I'm curious, how did you notice it wasn't charging?

 

[imiceman44]

As was suggested here try testing at the battery with a voltmeter don't rely on the voltmeter in the dash. second like dorian said try it above idle and see if you get enough voltage. If you still don't, try getting a wire from the positive post to the thick bolt on the back of the alternator and see if it works then, if it does and it doesn't without it, then you have a blown fusible link somewhere, you just need to find it.
Let us know what comes out of those new tests so we can continue with you. /forums/images/graemlins/thumb.gif

 

[txbartman]

Could also be the ground of the alternator. The alternator usually grounds to the block through the lower mount. To make mine work a little better, I run a grounding strap directly from the lower mount between the bolt and the alternator casing to the frame at a common mount with the battery negative.

Just a thought.

 

[AK-5GUY]

I know that the system isnt charging because on the night I brought it home the battery was dead. I put in a brand new battery and it started fine. But after driving it for a while I noticed that (1) the voltmeter wasnt working, (2) the windows didnt work, and (3) it would start to cut off sometimes and the lights would go dim and the heater fan would slow down. By the time I got to where I was going, (about 30 minutes away), the headlights were so dim I could barely see them and the battery would just barely start the truck. I put the battery in a different truck with a fine electrical system and charged it back up and it works fine now. I dont know when I will get back to working on my truck because I parked it quite a ways from my house untill I get the new engine. I hope to work on it soon, but im afraid that it wont be untill warmer weather. Thanks for the quick posts and great suggestions. Keep em commin. Harrison

 

[Panther]

I would make sure to check for any shorts in the wire running from the alt.

For it not to charge, either the alt is dying or the alt is not connected (correctly) to the battery. The latter would mean the alt is shorting to a ground on the truck.

And don't always trust voltage readings on a battery/alt. It's amps that start/run the truck. A nearly dead battery can still read a full 12V.

 

[MA87K5]

Check the ground straps. That won't hurt.

 

[Grim-Reaper]

There is several fusable links and not all of them are easy to get at. There is 2-3 down by the starter. Depending on your truck there is sometimes a pipe that the wires are routed through to protect them from the exhaust. Many times the fusible link is up in side that pipe. If your truck has 3 links one of the wires coming off the starter at the same terminal that the battery cable goes too "Y" for the second fusable link. The wires then go up to the fire wall. One of the wires will go to the juntion block on the fire wall to the left of the wiper motor. One goes dirrectly to the the junction plug into the back of the fuse box below the wiper motor. The alternator also has a fusable link that hangs down below the fire wall junction block next to the driverside valve cover that most people don't relize is there. Trace the alternator wire back to the fuse block. These alternators also require a "Feild" charge. That's the connection that plugs into the top of the alternator. If it doesn't have that feild voltage it will not kick into charging. Need to trace that back and make sure there is not a problem with that. It will be switched.
This may sound stupid but check your fuses. If you have a blown fues and it's the one that controls that feild circuit then it will cause this problem. Sometimes when a Alternator dies it will blow that fuse.
If you hit your local Library most have year spicific repair manuals on Microfisch. 10 cents a copy to get a wiring digram that will be correct for your truck.
Also if that motor has ever been out of the truck there is the possiblity that the wireharness was caught between the block and bell housing by accident and you have wires shorting out. Makes sure that didn't happen.
Personnaly I like using a test light and not a meter for checking stuff like this. A meeter can read voltages or resigual voltages with almost no amperage behind them and make you think there is usable power there when there is no amperage to drive that power. If you have standing/ residual voltage a test light will draw enough amperage to make that go away most of the time.