New engine electrical problems.

[Jakes-66-K10]

I've installed a new GM crate engine into my '70 Chev. I'm running into all kinds of problems, can someone answer a few of these questions?

One would be I have a weird wire attached to a light that is coming out of my steering column. Not even sure where that's supposed to go, or what it is.

Would someone mind giving me a breakdown on which of these wires go where. My wiring diagram shows the yellow and purple go to the starter, but perhaps the yellow is not needed anymore since I have an HEI?

And I know the greenwire in this pic is for my water temp, but what's the yellow wire supposed to be for? Both yellow wires seem to be coming out of the same wire into the fuse box. I am not completely ignorant to electrical things, but I could sure use some help on what wires are supposed to go where (treat me like a newb!). I'm really confused because it's a newer engine and some of these wires may not be needed. But I don't know...

Anyone up for this challenge to help get another truck on the road? I'm not getting any power anywhere, so could use a quick walkthrough wiring up a new engine.

[pjmoreland]

That wierd wire coming out of your steering column is actually a fiber optic line that transmits the light from that light bulb up to your shifter indicator. The bulb socket should be plugged into the back of your gauge panel. Based on the picture, it looks like you need a new bulb though. Usually when the bulb is silver like that it means the bulb is toast.

For a stock distributor with points and an external coil, power is provided to the ignition system by a special white wire that runs from the big square electrical connector on your firewall to the ignition system. This wire has a high resistance and drops the voltage down to about 6 volts, which is what the stock ignition system requires for operation. The yellow wire connects to the terminal on the starter motor that is farthest from the engine block. The other end connects to the coil, and provides a little extra voltage while cranking the engine over. If you are using an HEI distributor, you will not want to use the stock white ignition power wire, or the yellow wire. You will want to run a 10-gauge wire directly from the "ignition unfused" connection on your fuse block to the power terminal on the HEI distributor. The power terminal is the one that is closest to the firewall, assuming you have the distributor positioned with the connector terminals facing the driver side of the truck.

That black plastic terminal block mounted on the passenger side fender should have a wire connecting it to the + terminal on the battery. There should be another heavy gauge wire connected to that black plastic terminal block that runs into the headlight wiring harness. There may be a third smaller wire running into the wiring harness that powers the battery gauge on your dash, if you have one. That's probably the wire in your picture that has a fuse on it, but if it is, that' s not the stock fuse holder. The fat wire that runs from the black terminal block into the harness runs through a fusible link (basically a big fuse) and then connects to the big square connector on the firewall. It's the big fat red wire. You should be able to disconnect the square connector and measure 12 volts on this wire. This wire provides power basically for everything in the truck.

I'm a little concerned about the broken wire sticking off the black terminal block on your passenger fender. I'm guessing that is the wire that is supposed to connect to the + terminal of you battery.

The purple wire connects to the terminal of your starter motor that is closest to the engine block.

You will probably not be able to remount your temperature sensor in the head because the holes in newer heads are too small. I found a water neck (thermostat cover) from an 83 caprice that had the right size hole for the temperature sensor. Some aftermarket intake manifolds provide a hole for the temperature sensor, but usually the temperature sensor ends up interfering with the upper radiator hose.

[chickenwing]

Looks like PJ covered all your bases but the temp wire. Yellow wire looks aftermarket. Follow it back and make sure it has been spliced into the green wire. Insulation gets very brittle on the temp wire since its right there at the exhaust manifold. If I had spliced it, I would have removed the green wire alltogether.

Would like to see another pic of the junction box on the passenger fenderwell facing the battery so we can see were those wires tie into.

Edit: I plug my light tube into the socket to the right of the speedo (looking at front) in the center.

[Jakes-66-K10]

PJ, thank you SOOO much. I'll try some things tonight, that junction box may be the entire reason why I'm not getting juice anywhere. Chickenwing: The yellow wires are both spliced into the same white connection that comes from the fuse box in the firewall. Temp sensor is still wired up green and isn't spliced anywhere.

I'll take some more pics of the junction box tonight when I get home.

[Jakes-66-K10]

What is the difference between a "fusible link" and an inline fuse. If you look at this diagram, there are both going into the passenger side junction box. I know I have an inline fuse on my black wires. But as I am hooking up a wire to the positive battery terminal does "fusible link" mean it's just optional or something?

[pjmoreland]

A fusible link is essentially a high-amperage fuse that is difficult to replace. It's buried inside the wiring harness plastic wrap near the horn and external voltage regulator, and the wires are permanently attached (crimped) to it.

[Jakes-66-K10]

Hmm... that's not encouraging. According to this diagram, I need this fusable link between the battery and junction box. So if the previous owner cut the cable, and they are difficult to replace... what are my options?

[pjmoreland]

Usually when you buy a new battery cable that connects the + terminal to the starter motor, they come with a 6-12 inch piece of 14-gauge wire sticking out of the end that connects to the battery. This wire is some special kind that in itself is the fusible link. The one on my truck has "Fuselink 14 awg" printed on it. I suppose there is a remote possibility that you could buy a piece of this special wire from an auto parts store.

[68w/sbc406]

i have never heard the fact that it was a 'special' kind of wire, it is just a size smaller than the rest of the harness. that way just the begining of it is the weekest link and just that 6-12 inches will melt (14 awg wire will hold 15 amps where as 12 awg wire will hold 20 amps. the 14 will melt before the 12)

[pjmoreland]

I'd go along with that.

[BobbyK]

That cut black wire on the terminal block was most likely the fusable link.
They are actually easy to replace,granted,if you can find them.

You need a 14g fusable link to protect the fuse block.The main fuse block 12V supply connects to that terminal block on the pass. fender.
Inline though,should be that fuseable link.

You can get a fuseable link at just about any parts store.One end should have a ring terminal on it and the other end gets crimped and soldered onto the fuse block 12v feed wire.
Or connect one end of the fuseable link to the POS bat post and the other end to the terminal block on the pass. fender.

Without that fusable link to protect things,a short in any circuit that may be connected to the fuse block will result in an electrical fire if not noticed quickly.

With the fuseable link installed a short will happen and burn that fusable link up.That,in turn, disrupts power to that circuit.

[Jakes-66-K10]

Well good news! I did as you suggest PJ and went and bought new battery cables, and it did come with a little lead. I took that lead and spliced it into the junction on the passenger side, and *I HAVE POWER!* Feels great to see these old headlights, gauges, etc start working again. ITS ALIVE!

But BobbyK, you've got me worried about a possible fire. I don't understand what a fusible link is, I mean any wire could have a ring terminal and get crimped to another wire. I just don't understand how to tell if it's a fusible link, or what in the heck that means. But I'd sure like to learn.

[68w/sbc406]

its just the weakest link in your whole electrical system. if there is a problem with any part of your system, that link will fry. then you only have to find the problem not where is every place the wire is fryed, cause it will just be that 1 link

[BobbyK]

Here is what they look like.


And here is a little info. on them.(same site)
http://www.madelectrical.com/catalog/fusible-link.shtml

[pjmoreland]

The little lead that came with the battery cable is probably an adequate fusible link.

[chickenwing]

I'd verify that it was like PJs though and says fusible link on it. If not, onstall one.

[Jakes-66-K10]

Alright. I'll double check that. Now, as I am hooking up my electric choke and also the HEI, I need an inline fuse of 30 amp on HEI and no inline fuse for the choke, correct? And both of these can be spliced together to the Ignition Unfused if I understand what others have done.

[pjmoreland]

Personally I don't think the 30A fuse is necessary for the HEI power. If your HEI shorts out for some odd reason, and draws over 30A, the fusible link between the battery and the terminal on the fender should fry first. Of course it certainly can't hurt anything to put a fuse in the wire to the HEI. I would connect your electric choke to the "Ignition Unfused" terminal as well. That's how I have mine.