Wiring Questions

After talking to several people and reading several forums, I am swapping to HEI from the prestolite ignition.


1) My 1975 CJ5 with the 232 has a dark purple wire and a light purple w/ wht tracer wire in the loom that were cut near the coil. I didn't know they were there until I opened up the loom to clean up some wiring. I can't figure out what they are/were for?

2) I have the wiring diagram for the HEI where I plan to use a relay to power the new distributor. The diagram shows me pulling 12V from the I post on the solenoid and the switch power will come from the existing coil positive wire (if im understanding that correctly, I'm a newbie).

2a) So my question is, my positive battery cable has a small pig tail on it. Could I not just use that to supply the 12V to the relay instead of running a longer wire to the I post on the solenoid?

3) I have a light blue wire coming off the starter solenoid that is on a small post. Does this stay as it was before? My wiring diagram shows it as going to the ignition switch. I just wanted to make sure I have everything right.

I know there has been extensive coverage over the HEI swap and I think I have it all figured out, hopefully that question is worthy of another thread as I don't want to beat a dead horse.

 

You need to refer to the wiring diagram in the '75 TSM. Trace it through. I can't help you right now, but if you refer to the TSM you should be able to follow the wires and understand what everything is.

You will be removing the Prestolite module from the inner fender. It has a power wire that can power your new distributor. I would not add a relay.

 

I think I found a better wiring diagram and traced the purple wires. The power wire that went to the coil is 14ga and then to the module was 16ga. I planned on using at least 12ga for the new distributor and I think this is why the relay was recommended. Will the 14ga wire be enough to supply the new HEI distributor?

 

12 gauge is HUGE in automotive systems.

 

The diagram calls for 10 or 12 ga

 

12 gauge wire is rated at 20 amps

 

IMO, unless you are planning of running the engine over 6000 RPM, you don’t need a relay.

What is going on it this. The ignition coil needs to get saturated before it can fire off. This takes a little amount of time because at it’s heart, it’s still an inductor and take time to “charge” up. At the correct time, the points open up and all that stored up power is discharged through the spark plug. The faster the engine is spinning faster, there is less time for the coil to get saturated and then the spark gets weaker. If your wiring cannot supply enough power because the wire gauge is restricting current, then the coil cannot charge up fast enough. However, at 3000 RPM, there is plenty of time to saturate the coil.

12 ga wire should be good enough as long as the wire going to the ignition switch is of the same gauge or bigger.

It’s kinda like a home toilet. There is a small pipe filling the tank up. It takes some time to fill the tank but when you flush, a lot of water flows out quickly to flush everything away. The quicker you flush, the less time the tank has to fill up and eventually the flush is to weak to work properly. If you put a garden hose to the tank, it will fill the tank up quicker and you can flush more often.

 

Good analogy for a newbie like me. That makes sense to me.

 

No.#1 question is likely wires to the oil and temp gauges.

 

x2, John is good at explaining electronic situations for us electronically challenged folks.

 

After getting a better wiring diagram, I have decided that to be the case as well. I found what I believe to be the temp sensor (top of the motor, front and center) with a red wire very poorly ran through a random spot in the fire wall.

I can't seem to find the oil pressure sensor although that seems to be one of my working gauages on my dash.

I've always been horrible at electrical but I actually have found this pretty soothing...going slowly and removing wiring and cleaning things back up according to the shop manual. Thanks for the reply.

 

Looking at the factory wiring diagram, there is a 14 ga wire that comes from the ignition switch to feed the factory Prestolite module, the factory coil, and the exciter wire of the factory alternator. I have to wonder what additional stuff is in the HEI distributor that needs a better connection than the factory provides to their coil and their ignition module. I would say nothing, but I have no evidence.

At the top of this thread, I suggested to the OP that he use this wire to power his distributor. I understand the conflict this poses to him - if the instructions say to use a 10 ga or 12 ga wire, that's a pretty good reason to use that size wire. On the Jeep, the existing wire all the way from the ignition switch is 14 ga, and splicing in bigger wire somewhere along that line doesn't provide any advantage. If you want to go bigger, the relay makes sense. Then you use the ignition feed to switch the relay, and run your 10 ga or 12 ga wire direct from the solenoid to the relay to the distributor. Same idea as what you see in this thread. Headlights Relays In Absurd Detail

Certainly the bigger wire and relay won't hurt anything. It's just more stuff to do and more parts that could break at some point. The Bosch type relays are very reliable, and if he routes and dresses the wire properly, he should have no trouble.

John's analogy is correct as far as it goes, but I think the problem is the scale of what we are discussing. A 12 ga wire is about 1.5 times the cross section area of a 14 ga wire. This means you are filling the toilet tank with a 5" diameter fire hose instead of a 4" diameter fire hose. In practical terms, I don't think this reduction in wire size will have a detectable effect. The smaller wire will have more resistance and make more heat, so the coil will charge slightly slower, but it's a really tiny difference. John also correctly points out that this engine will never see engine speeds where the coil charging rate might make a difference. It's a 232 and unlikely to see over 4500 RPM, much less 6000 (peak HP is at 3600). And it's a six, which has a 1/3 longer dwell than a V8 and fires 1/3 less often. It's a light load for the HEI parts.

Another question the OP had about the battery cable. No, I would not use that lead off the positive cable. A cable with an extra lead like that is a ground cable, meant to go on the negative battery terminal and connect to the body steel. I suggest you replace it with a proper positive-side cable and take your relay feed from the starter solenoid post, as shown in the thread linked above. Indeed, if you want, you can put a small distribution panel close to the solenoid and run any accessories you might want from that panel. That will give you expansion room for new stuff, without cutting in to the factory harness. Waytek or Del City have plenty of such panels to choose from. Fuse Panel & Terminal Strip Connector Types The solenoid is the best place to feed this panel from.

 

Over the right fender, facing the distributor. Bottom rear of the block, centered in the lower left corner.

 

Both Neg and positive cables come with pig-tails. I have both on my Jeep but use only the neg pig-tail at present.

 

Apparently Deka sells a red cable with an extra lead for this application, which they tell you to cut off or tape over.

1975 JEEP CJ5 3.8L 232cid L6 Battery Cable | RockAuto

I have never seen a positive cable with an extra lead like this, as parts or in service. I still think it's a bad idea, because it's not fused and connects directly to the battery. The fusible links in the factory wiring are there to protect the car from the battery, and a connection like this bypasses this protectlion - at least it will until the extra lead melts in two.

 

Definitely the positive cable with a pigtail like that. I see them a lot locally but mostly at farm and tractor stores. Occasionally at auto stores.

My question, purely out of ignorance, is how would pulling power from the starter solenoid which appears to be directly connected to the battery be any different than pulling power from the batter pigtail? Genuine question, I will pull power from the solenoid as the wiring diagram i have suggests and as you have suggested so I can do it right.

If you think the 14ga wire that originally fed the coil is enough, would I simply splice in to that wire and put it on the BATT terminal of the new distributor? Thus, getting rid of the relay and additional wiring?

 

My opinion - You go directly from the solenoid to a circuit breaker, permanently mounted to the fender. Using the wire coming from the battery post connector, you must leave a long unprotected extra wire connected to the battery cable so you can still take the battery cable off of the post and remove the battery. I connect to the solenoid like here -



The wire that's not protected by the circuit breaker is as short as possible, does not move, and is routed in a protected location. It's also covered with plastic wire loom, which protects the wire from sharp edges and abrasion. This is what I meant by proper routing and dressing of the wire.

Yep, that's sort-of what I've done. My CJ-6 came to me with the Prestolite stuff, and I am running "Stealth HEI" using a HEI module triggered by a Duraspark distributor. I have a Pertronix "high energy" coil that fits in the original coil clamp. MSD makes a similar coil. Works fine for me. I take the former module power lead to run the HEI module.

But do what makes you comfortable with the result. Done properly, I don't see any harm in adding the heavier wire and relay.

Also mention - when you disconnect or R&R the battery, you always take the negative cable off first, and put the negative cable on last, assuming you have negative ground of course.

 

First thing my Dad ever taught me. I can never hook up a battery without thinking of him.

That, and "don't ever wrap your thumb around the crank!"

 

I agree with using a fused relay and #12 wire. With this you can incorporate a hidden kill switch and reduces the current through the ignition switch. A shorter wire means less resistance [heat] and the security of knowing there is a good constant source of power to the coil. Use the same relay for lights, fan, etc. Carry a spare relay or two.

My heater fan is the highest current draw inside the cab.