Hey all,
I recently did a battery relocation on my 99 GS300. Moved the battery from the front, to the trunk. I used 1/0 AWG wire from the battery, to a 250amp fuse, then to a junction block in the engine bay, where I have the stater, and fuse box connected to (fuse box is charged by the alternator on this car or so it looks) than I have 1/0AWG wire from the negative straight to the chassis in the trunk and than 1/0 from the chassis in the engine bay to the engine block. My grounds seem fine, and the car starts and will charge fine at idle, but when I turn my accessories on, radio, lights, heat, the voltage starts to drop very fast. When checking with a multi meter and no accessories on, battery seems to stay charged at about 14.07 volts. When accessories are on, it drops about .5 volts every 2 minutes or so, it got down to 12.13 volts and kept going until I turned off the accessories then it only charged itself up to about 13.6. Is this normal or does this seem like an alternator issue?
I cant drive the car around yet, I have a tuning session scheduled for may, so only been able to see this at idle. Perhaps this alternator which is the original is just no good or can’t keep up with the load at idle rpm?
I noticed this when I removed it too, this metal piece was broken on the back and I don’t know how important it is. Removed it because I ordered a new one to see if that helps my issue. But I’m still asking on the forum to see if I’m chasing the wrong thing. I have added gauges, a higher flow fuel pump and larger injectors, the stereo is after market but I don’t have a sound system with it. I wouldn’t think these would put that much more stress on the alternator . Any hep would be appreciated.


Is this some sort of grounding piece?

 

I think some auto parts stores still have alternator tasters. You could have the old one checked and see if a new one is the fix.

 

Ya, u need to find how much power your old alternator was putting out. When u move the battery to te trunk and asked the longer cables, there will be some voltage drop, make the serpentine belt is fresh, and isn’t slipping or anything

 

well that’s why I updated the wire from I believe original size was 4awg to the larger 1/0 AWG. Power house racing sells a relocation kit for the IS300 that uses this size, so that’s why I figured it would also be okay for the GS. Serp. Belt is brand new it came with my A/C delete bracket, and is pretty tight. Also, now the A/C fan and radiator fan both reference the coolant temp to activate, instead of A/C fan referencing A/C pressure. It works as it should, and only turns on once coolant reaches 190 then turns off when it gets back down to 170-175.

 

I relocated the battery to my trunk early on in my mods. The OEM alternator was always fine to run the car for years. I used 0 or 1 gauge cables, can't remember. What I did find out was that the cranking is difficult for the battery and was always weak. So I upped to a 94r which is the most affordable of the larger batteries. 850cca and a larger reserve capacity helps a lot for the relocation. I have a DC Power 180 amp alternator installed now, but that that didn't make a difference in any normal conditions. I simply wanted to ensure maximum ignition power when pushing the engine.
In short, my experience is that the OEM alternator didn't produce less voltage because the battery was relocated. You may just have a weak alternator. Have it tested. They will run it through load conditions and see if it can produce sufficient voltage under load. If it is good, you may have a problem with what you set up at the junctions you spoke of.

 

do you remember if you had to upgrade the wire that goes from the alternator to the fuse box or did you leave that as it was, and just upgrade the power and ground wires from the battery to the front of the car?

 

So I replaced the alternator and it did help the charging issue. However, with all accessories one (except A/C due to A/C delete I did) heater blower, headlights, radio and fan running, the charge goes down to 13.8 and very slowly continues to drop (.01 volts every like 20 seconds) but not significantly enough to make any difference. Mind you, this is all while idling in the drive way. I also noticed that the rpm’s drop when the electrics load is increased, I thought the rpm’s were supposed to increase with the increase of electrical load? Please correct me and enlighten me if I am wrong. Thank you.

 

I left the wiring to fuse box alone. Just a big cable from the alternator to the battery and a nice size ground to chassis in the trunk. If you upgrade the starter power cable too, then it's what's known as the "Big 3 mod". I haven't observed a need to do it though.