1972 FJ40 V8 Conversion Wiring Harness Issue (2 Viewers)

[texcwa]

I performed a sbc V8 swap about 12 years ago. When I did the conversion, I used the existing harness and have my 1 wire alternator running through the Amp gauge on dash. Did not do any other re-wiring. Recently, I added the Holley Sniper EFI and Hyperspark Ignition (major improvement). I have also added a Stereo and a couple of other gauges and have added another fuse block in the engine bay that is tapped off one of my fuses so to have additional ignition switched sources for other accessories. I am now noticing that I am losing voltage to my battery. My alternator is putting out 14.32 v but the battery does not see this (more than a volt drop). I have also read that it is not advisable to run additional currant (amperage) through the dashboard amp gauge (have read can cause wires to burn and even start a fire?).

I tried to just disconnect the alternator wire to existing harness and running it straight to the battery but when I did this it caused the relay in my high-pressure full pump to kick on (even though the existing wire from alternator to harness was disconnected, makes no since).

I am thinking that since the alternator is running through the dash amp gauge, and through the ignition and fuse block through undersized existing wires is why I am losing voltage to the battery.

So, looking for some help from anyone who may have experience in the wiring of these FJs or has done a V8 conversion and may be able to assist on what I should do. I have attached 2 diagrams below, one showing what I have verified is running through my fuse block (and what I have tapped into for other accessories) and a 2nd showing the FJ40 wiring harness with the wires identified that I need to modify. Also note that the wiring diagram shows many sources (such as head lights) originally running off the separate alternator regulator that I no longer have since the 1 wire alternator has regulator built in, so all power is running through harness and fuse block.

 

[B y r o n]

Hopefully when you wired in the second fuse block you ran the wire from fuse #4 to a relay trigger connector. You also ran a power wire from the battery to the relay power connector and from the other power connector terminal to the new fuse box.

This way you're really not drawing much from the original fuse panel, only triggering the relay when the ignition is switched on. Power is then coming straight from the battery to the secondary fuse block to power your accessories.

Additional reading material.

 

[texcwa]

Hopefully when you wired in the second fuse block you ran the wire from fuse #4 to a relay trigger connector. You also ran a power wire from the battery to the relay power connector and from the other power connector terminal to the new fuse box.

This way you're really not drawing much from the original fuse panel, only triggering the relay when the ignition is switched on. Power is then coming straight from the battery to the secondary fuse block to power your accessories.

Additional reading material.

Great idea will add a relay. I have used relays on several other accessories such as the fuel pump and the EFI so not to have a dirty wire. But I still have my original issue with the dash amp meter.

 

[pb4ugo]

You might look at the tutorials on mad electricals website. They go into detail about using the wiring for an ammeter and the benefits to wiring it a different way like 1 or 3 wire alt. I hooked my GM alt charge wire to the batt. to avoid charging the batt thru stk wiring harness and ammeter. I use the batt as the junction box. Wiring to the batt basically makes the ammeter not work. Power just goes thru it, or you just hook the 2 wire together.

 

[B y r o n]

So it's been to many years since I did my 355 SBC conversion, mid to late 80's. So to refresh my memory I looked over the info here. According to this info the charge wire from the alternator needs to go to the battery positive cable. The charge wire also needs to be sized appropriately for the alternator output. The alternator should also be grounded to mounting bracket or block. Your diagram shows no ground. There should also be a ground cable from the block to the frame. Wired like this your battery should see the same, or close, amperage/volts put out by the alternator.

 

[texcwa]

You might look at the tutorials on mad electricals website. They go into detail about using the wiring for an ammeter and the benefits to wiring it a different way like 1 or 3 wire alt. I hooked my GM alt charge wire to the batt. to avoid charging the batt thru stk wiring harness and ammeter. I use the batt as the junction box. Wiring to the batt basically makes the ammeter not work. Power just goes thru it, or you just hook the 2 wire together.

Thanks, and I have reviewed a couple of their articles, they contain allot of information. What happened to me was that when I disconnected the hot wire from the single wire alternator, kept it off (taped over wire end so not to have it touch any grounds) then just put a new 12ga wire from alternator to battery + (no other power was connected and ignition key was off), my fuel pump relay that's only connected to my EFI through a 12v ignition on wire (the original coil wire) blew and the fuel pump turned on?? I have no idea how power made it to the fuel pump relay with everything off and only touching the alternator positive terminal (with nothing else connected to alternator) to battery +. Very confusing.

 

[texcwa]

So it's been to many years since I did my 355 SBC conversion, mid to late 80's. So to refresh my memory I looked over the info here. According to this info the charge wire from the alternator needs to go to the battery positive cable. The charge wire also needs to be sized appropriately for the alternator output. The alternator should also be grounded to mounting bracket or block. Your diagram shows no ground. There should also be a ground cable from the block to the frame. Wired like this your battery should see the same, or close, amperage/volts put out by the alternator.

Byron, I checked my grounds, all good, battery - to motor, motor to body, alternator grounded by brackets (I have never had any issues with the 1 wire alternator since installing 10+ years ago). The voltage drop was really not my concern, it was an indicator of something going on. The real issue is wanting to and how to get around the dash amp meter and having all the alternator currant running through the harnnes to get back to the battery.

As for running the proper ga wire directly from alternator to battery +, see my response on thread #6 above. It is very confusing. What I am thinking of doing (but do not want to cause an issue especially with the computer built into the new Holley EFI) are to do the following: (ref to my wiring diagram on 1st post)

1. Disconnect the red wire from battery to dash amp meter at the amp meter (I colored it red it's actually identified as a White wire)

2. Remove the portion of what I colored Blue wire from dash amp meter (actually identified as a White wire with Light Purple Stripe) The balance of this wire (I showed as Blue) from alternator to Amp meter will not be used.

3. Tie the end of old White wire (what I showed as Red) where removed from at Amp gage (Item 1 above) and tie it to the White with Purple Stripe (I showed as Blue) that I removed from Amp meter, ref Item 2. This would supply the positive power to the ignition switch and fuse block and stop the currant from alternator through wiring harness back to battery.

4. Install a new proper sized power wire from alternator to battery +.

It seems to me that this would stop the currant from having to travel through the old wiring harness, supply currant to the ignition switch and fuse block, disconnect the amp meter, and supply full currant to the battery from the alternator. I would then install a new Volt meter next to my secondary water temp and oil pressure 2" gauges I already have. Ref Diagram below:


Any thoughts?

 

[pb4ugo]

Are you running a gm alt?

 

[texcwa]

Are you running a gm alt?

No, not a 3 wire gm, just a 1 wire 80 amp by summit racing.