Quil

I'm at the point of my swap where I'm ready to tackle the wiring harness and run all the wires for constant/switched power to the fuse/relay center provided with my PSI harness, as well as the wiring to the electric fans and fuel pump. I thought I'd make a separate thread where anyone could post tips or advice, or come in and ask questions.

I punched through the firewall today and have all the engine connections done with the exception of the O2 sensors, which I'll hook up once the exhaust is in place. Couple questions about the alternator setup...

I read somewhere that when you're using a stock LS wiring harness, that all you need to do for the alternator is plug in the connector from the harness and then connect the ring terminal for power from the stock C3 harness to the back of the alt...is that correct? Can I just tape back or remove the remaining wires from the C3 harness?

Also in regards to the alternator/battery...what do I need to do to use the stock "battery" gauge with the swap? I think I have the rest of the gauges figured out, but not real sure about the battery gauge.

Tomorrow I'll wire constant and switched power to the fuse/relay center, and then start wiring the fuel pump and the relays for the fans. Jon at PSI sent me a diagram to use for wiring up the fans...if you're using the supplied fan 1 and fan 2 wires from his harness, you would substitute them for the temp switch in this diagram and connect them to 86 on the relay. Here's the diagram for future reference...



Thanks in advance. Please feel free to add to the thread as you see fit.

72LS1Vette

That's what I did for the alternator. I just left the original alternator connector hanging since it was out of the way. The Amp gauge still worked normally. I think that is tapped off the horn relay or somewere like that.

I use the fan1 signal from the ECU to run the fan relay.



Rick B.

Quil

Man, it can't be that easy! Thanks!

Neptune75

great thread idea! just yesterday i pulled my harness through the firewall, hooked up all engine connections except the o2 sensors. getting ready to wire dual fans and oem fuel pump in tank.

Quil

Nice. Where are you locating your PCM? I'm shooting for under the dash...I don't have AC so that should help. Still gonna be tight.

Neptune75

Also in regards to the alternator/battery...what do I need to do to use the stock "battery" gauge with the swap? I think I have the rest of the gauges figured out, but not real sure about the battery gauge.



Q.... what wire runs the "battery gauge".. is the 2nd wire that goes to the old alternator? i mounted my pcm behind the center gauge cluster. i'm going to install vintage air one of these days..

Garys 68

Um the stock 68 gauge on mine was not that simple. The stock alternator was about 60 amps, some LSx alternators are over 200 amps.
I completely rewired mine and tested resistors for the stock meter to get it working correctly.
If you isolate big current items (fans, fuel pump) outside of your current dash harness, it wont be affected. That would be my suggestion. I took the complicated route, but my gauge reads correctly.
A voltmeter would be much simpler.

Quil

I was curious about that myself, but like Rick said above, I think the gauge measures current at the horn relay, and not directly off a wire from the alt. I'm really not sure how it works to be honest.

Still hunting a good place for my PCM. Were you able to mount yours there with all the ductwork in place?

Neptune75

Q. i will get some pics up this weekend when i get a chance to work on the car... i have no heater/ no ac at the moment.. but i have plans to do the vintage air next year. i only drive from mid may to oct. here in a michigan summer a/c is really not needed. but i "luxury" i would like to have someday.

Garys 68

The existing battery gauge works like an ammeter. But instead of a shunt resistor, it uses the existing wiring between the distribution point (horn relay) and the battery source (starter battery post). If you are using the vettes current wiring, you can hook up the big amperage items (electric fans) off the alternator output and your gauge should work correctly.
However, if the fans pull more current from the battery (motor not running) or the 200 amp alternator is charging a very dead battery, it can overwhelm the systems capabilities and burn out the battery gauge.
I replaced all the wiring on my LS swap, including larger alternator to starter wire. When I wired in the battery gauge, I tested with resistors in the wire to the battery gauge to get the reading correct.

Quil

OK, I have 99% of the wiring completed. I have to admit my idiot mistake in wiring the fuel pump initially with 16ga wire...doh. Went back and rewired that, and got all my fan relays and everything routed. So I'm just tying up a couple loose ends and the wiring will be done.

I went to hook up my stock C3 wiring to the alternator post, and both the heavy pink wire and the black wire have ring terminals roughly the same size...I'm assuming the heavy pink wire is the one I need to hook to the back of the alternator, and not the black? Just wanted to be sure before I fried everything...

1980LS53

I have a question before I start changing everything, I have a 1980 and am putting a 5.3 in it. I pulled the harness off to convert it to a 5 wire set up. Before I do that I wanted to addesss my gauges. I am using a 4l60e and wanted to keep it electronic. I'm sure autometer or someone makes an analog to digital convertor but then I need to figure out oil pressure etc.. So is there a smarter way to do this??

Also I have a diagram for the 5 wire set up but if anyone can ginve me another i would appreciate it as there seem to be a few problems with the one I have.

Jason

Vettegineer

Hi Jason--I've found on the oil pressure gauge it is easiest to tap the oil cooler delete plate (near oil filter--google it) and then install the original sending unit there. The engine will have a separate sensor--but you need not use the same signal.

For the 4L60, if it is a gen 3 (26 tooth) then the ECu will drive it. If it is a gen 4, then you need a controller. I bought the TCI controller.

My system isn't complete yet--I'd really like to know/see where you guys have mounted the new fuse box (if you have one--like the gmpp system,) and where your computers are. I have factory air, and I'm not liking the engine bay spaces-- if you've done it take some photos!

72LS1Vette

I know the washer bottle is in a different location in later years but here is where I mounted the ECU in the 72.




The fuses and relays are attached to a panel that I mounted in the jack compartment behind the passenger seat.






Rick B.

DEEPSEA70

I mounted my PCM on a bracket attached to the dry sump tank, and had my harness extended about 5 feet to fit in the jack compartment.

rnoe124@charter.net

Would you be willing to show or tell me what all wires to the horn relay? I have a 73 that I've put an ls1 in with psi harness and fan relay. Just can't figure out the horn relay purpose. How many wires does the alternator have, and does it only connect to the harness or is there a wire running from alternator to starter?

RowdyMT

I'm just starting a swap in my 73 and Im looking for any current info for c3's. I've been through the huge thread several times but it hasn't been updated in years. If anyone can point me in the right direction for info or tips on the harness install/integration with body harness I'd really appreciate it!