ive recently upgraded my stock 90a alt. so the gm cs144 150a. all works good (finally). charges 14+ volts. but when i put load to it, my interior lights dim. now when i say load, i mean my turn signals lol. for example. when my turn signals are on, my ABS light dims as the signals blink. now, if i get more demand, such as park lights, its at a constant dim, obviously. now if i turn on my headlights, its like it cant handle the load. the fuel and temp guages go way up as a result and the headlights are baringly dim. is like ive got a ground not grounding somewhere. both upper and lower engine grounds are clean and perfect. batteries are grounded to the frame. all connecions between batteries, terminals, etc. are perfectly clean and neat. i just dont get it. the cs144 is charging, ive voltage tested it. plus i disconnected the battery and it still poweres the car.

I think I'd confirm the available current from the alt by measuring the draw on a semi-discharged battery.
It really sounds like either a bad gnd or alt is not putting out the advertised current (due to poor gnd?).

Obviously, you are not getting the current needed if lights go dim when the battery is under additional load.

i know it can be dangerous, but ive disconnected the batteries and the engine runs fine, but still begins to do weird things when under electrical load...im thinking the alt. is no good.

im assuming the alt. grounds when its bolted to the block? my starter wasnt grounding out a few days ago and had to put another ground wire closer to the starter

Certainly possible by all means. Do you have something that is capable of measuring high current flow? There used to be available a closely coupled meter that would measure starter current draw. It just sits on the heavy wire that feeds your starter and would give a amperage draw reading.

Of course to draw a big current from the alt, you will have to discharge your battery and then perhaps boost your truck from a static battery to start it. Your alt should give you max amperage for a few sec/min until the battery comes back up to close to full charge.

It's possible I guess that the alt could be faulty but they usually work or not work.
Do a simple ohms test from the alt casing to the neg post of your battery and see how good your ground is. Theory says it should be 0 ohms but less than 1 is good.

Do your lights dim at all rpm of the engine or is it at idle?

well ive got a multimetre with a clamp so i could draw down the battery and do an amperage test when i start up the car. ill try the ground test on the casing. thanks alot.

Just thought of something !

An ohms test MIGHT show a poor ground but it's possible to show good gnd using the milliamps that a ohmmeter uses to test continuity but under heavy current draw it could be not enough.

Use a booster cable clamped from the alt. casing to the neg battery terminal to make sure you are adequately grounded for big current applications.

Did an ohms test. Alt. is grounded 00.00 but the ground thats ontop the valve cover is about .6 or something. Far from 0 or 1 like you mentioned. So that could be a culprit. When i get some more 4 guage connectors ill reground the top of the engine down to the frame like the lower engine ground is.

Actually, .6 ohm is almost short but probably a little higher due to valve cover gaskets preventing really good contact with the block.
That won't be the source of your problem IMO.

Just a thought...were you fooling around with your fuse/relay block?

If you use GM alternator, you are totally destroying the reliability of a good 4runner.

You are already experiencing it.

very intimate with my fuse box lately yes. diking around earlier i blew the 100a alt. fuse. so replacing it involved tearing the whole thing apart. whatcha thinking?

Not necessarily true.

There have been many people that do this upgrade, and have not had any problems with their rig. The stock alternator doesn't put out the required amps for people that have a lot of electrical stuff on the rig, and this mod helps to take care of that.

OP, you definitely have a wire problem somewhere. Where did you get your information on doing the swap?

Did you solder and heat shrink, or just crimp everything together?

I'm sure you upgraded the wiring from the alt to the fuze block, and to the battery, but did you get the fuze too?

Not trying to say anything about your skill level or intelligence, I've just found out the hard way that complex problems are more than likely a simple solution after you've tried everything else.

Hmmmm.....Do a check to see if your alt is putting out good current by doing a battery drain then make sure your alt can put out 20-30-40-150 amps...it don't matter right now. It don't have to be 150 amps.

What I'm thinking is there is a bad connection from your battery to the fender well fuse box or from your fuse box to your interior fuse box.

If you were to monitor the voltage inside the truck on the interior fuse panel you may find it's a long way from solid 12+ volts thus causing other things to malfunction due to low voltage.

You better re-check in that area with a voltmeter making sure all connections are tight and making good contact.

thanks alot doc. i dont remember where i got my info from. i scowered many threads on different forums on how to wire this properly. all seemed to stear my in the same direction. i just hacked off the denso plug and hard wired a new gm pigtail to the corresponding wires. (dont remember what goes where) none of my connections are soldered because ive always been ****ty at soldering, either that or never new how to properly do it. but every connections is heatshrunk. all the wiring between batteries, starter alt, and fuse block is redone with 4 guage. all pretty looking. but no fuse...fuse for what? the alt?

and grenvilleter. i havent had the chance yet to do an amerage test on a drained battery yet. both batteries and the lower block ground are grounded dow to the frame. the only ground thats not a 100% sold ground if the upper ground off the valve cover. that ones just to the firewall, on my list to relocate to the frame.
im thinking its fuse box related too. because ever since i blew that 100a. alt. fuse ive been having these weird problems. (besides my starter not grounding)...i checked and doible checked i didnt miss any thing when i put the new fuse back in. in order to test the voltage in the interior fuse box, how would i. if i take a fuse out to stick a prob in there it stops te circuit, thus now flowing 12v...shed some light on how to test voltage in a fuse box?

wow...thats the longest post ive ever posted lol. i appreciate your help guys. ive been battling this for so long. but i refuse to get someone else to fix it. neither do i trust anyone with my truck. its mine, i built it, i fix EVERYTHING my self. up until gears...i dont do gears, trannys, or engines lol. everything else. i do. lol