I've recently been having issues with an alternator on its last legs, squealing like a banshee and tach readings all over the place. I've been pushing my luck before replacement and today the tach, speedometer, fuel gauge and temp gauge all went dead at the same time.

I got to where I needed to go and couldn't start the car. Had to jump it and drove all the way home, about 30 miles, fine.

Here comes the fun part.

I got home and replaced the alternator with a one wire alternator and couldn't start the car. We tried to jump it several times and went through a whole myriad of steps to figure out if there was anything I was missing.

The battery is new. The one wire from the alternator is going through a 250amp fuse to the battery. The exciter and the tach wires are tapped off. After a bit the car finally started randomly and we've decided that my starter is prob going out as well, meaning that the jump I pulled to start the car prob had nothing to do with actually starting the car as it was prob the starter. Or it was a combination of both considering my whole instrument cluster died on me. I can deal with that. I don't mind replacing a 15 year old alternator.

What I don't get, I'm horrible at electrical as I'm sure you can all tell by now, is that now that everything runs when the starter actually cranks im still not getting any power to any of the other gauges. The blinkers and other lights work fine.

I realize that the tach gets a read off the lucas alternator but shouldn't I still get power to the other gauges? I'm completely bypassing the old 100amp alternator fuse under the hood now and im not sure if that is my problem or the fact that I'm not using the other two wires from the old alt.

Sorry for the block of text. If anyone has any insight I'd greatly appreciate it. I'll repeat the fact that I'm absolutely horrible at electrical but if someone could tell me exactly what I need to look at that would be great.

 

1. How about a pix of this one wire alternator, and what did it come from? You will have great interest in "alternative" alternators.

2. Big wire from alternator does not go to battery, but could. Normally it goes to one of the front bolts in the under hood fuse box. The other bolt goes to a short wire to battery positive terminal. If that little wire was not there, you would be charging the battery, but have no battery power to the rest of the truck.

3. Two smaller wires on back of stock alternator. One that bolts down is from the "check battery light " on dash. Without it, the multiwire alternator won't prooduce output. Small wire with push on lead is an AC signal that drives the tach, if it is off no tach signal. Could use an Ultra Gauge for a tach.

 

It's a powerbastards 220 alternator. 220AMP Alternator for Imports and Domestics - Fitzall-220 | PowerBastards.com I haven't finished installing a bracket on the lower half.

So yea. I just ran a 0 gauge wire I already had with their inline 220amp fuse straight to the battery. The old power line I just sealed with heatshrink tube. As you can see it is still connected to the fuse box to the battery.

Am I wrong in assuming that 100amp fuse is isolated in the box?

I like the idea of the ultra gauge btw.

 

just tooka look at the back of the circut board on the instrument panel. three of the printed circuit lines have the coating scraped off.

That is prob it.

 

re: I'll repeat the fact that I'm absolutely horrible at electrical

I would be inclined to believe otherwise.

Just checked my under hood box, when facing the box, the lead from alternator would have been on terminal that is closer to the alternator. The 100 amp fuselink now has no alternator on one end, no problem. OK where you have it. Battery volts from (-) post to each of the fuse link bolts, on each side of fuse links, should read whatever the battery voltage is.

When you do have truck running, voltage across battery should be between 13.8 and 14.4, what kind of volts do you have?

 

Ok i feel like an idiot. I thought i checked all the fuses last night with a friend. Guess I missed the instrument panel fuse..... I'll blame it on the half case of Pabst.

I have to get a meter to check everything out and report back to you just to make sure everything is ok in the long run but I'm pretty sure that the damage to the board caused the short.

Do I need to worry about the dummy light at all or can I just leave it taped off?

 

I'm pretty sure the GEMS computer needs a tach signal too.

EDIT: I could be wrong about that. I know the older lucas trucks had an input for the tach signal... but maybe the GEMS just use the crank sensor for that info.

 

GEMS gets engine rpm from the CKP sensor. You can unplug tach wire from truck and truck will still run. Don't have a place to tie the wire to, unless wiring diagram from new alternator shows something, so leave it taped.

 

after i replaced my alternator, everything charged perfectly but the damn tach still does not work right. when i start the truck the needle is about 1500 rpm and stays there unless i really rev it then it jumps up then back down its either at 1500 or 1500 lol unless i turn the engine off the the tach rolls up to the 12oclock position.

 

And if you unplug tach wire (flying lead) - does tach return to zero?