1994 Volvo 7.4 GL Alternator Wiring

[jmsmieja]

Hey Everyone,

I searched the forums but can't find anything to help me on this topic.

I just picked up a 1994 Chris Craft 268 Concept, and it has a 93/94 VP 7.4GL DPDM in it. When I bought it, it had new batteries, and I luckily discovered before being left dead in the water that the alternator isn't putting out any significant voltage (~4V at 3k RPM). I then noticed that the fusible link isn't connected to anything. It's hooked to the alternator, but there's no wire crimped to it and I found the cut wire that goes to the starter looking cleanly cut where it comes out of the engine harness by the alternator.

The boat does have a battery isolator, which appears to be added aftermarket, with a new wire (~10 awg) coming off the alternator, going to the isolator, and then splitting to 2 terminals that go inside the battery selector (I have a 2 battery setup). The battery selector is a 1/2/all/off, and it then has 3 large cables that go to each battery as well as to the starter.

I have 3 questions.

1.) Does it make sense that the fusible link is no longer part of the circuit with a battery isolator installed?
2.) Would a new alternator fix this problem, or do I need to dig deeper to see if there are any other wiring issues before replacing parts? (I started doing continuity checks and get high impedance continuity to frame through some of the alternator +leads - like the one hooked up to the choke stat on my carb)
3.) Does anyone have access to information, or possibly the same setup in their boat, and would be willing to show me how things are supposed to be?

I have plenty more information if needed about the other components involved. Let me know if they will help.

Thanks!

 

[Don S]

Re: 1994 Volvo 7.4 GL Alternator Wiring

1.) Does it make sense that the fusible link is no longer part of the circuit with a battery isolator installed?

There isn't supposed to be any fuses or circuit breakers

2.) Would a new alternator fix this problem, or do I need to dig deeper to see if there are any other wiring issues before replacing parts? (I started doing continuity checks and get high impedance continuity to frame through some of the alternator +leads - like the one hooked up to the choke stat on my carb)
3.) Does anyone have access to information, or possibly the same setup in their boat, and would be willing to show me how things are supposed to be?

Here is the electrical manual for that model. Testing the alternator is in the charging section.

 

[jmsmieja]

Re: 1994 Volvo 7.4 GL Alternator Wiring

Don,

Thank you for such a fast reply. I was hoping you'd respond. I've already started going through the info you sent and will let you know what I find.

I am curious, if you were going to add a battery isolator, would you have just cut off the positive wire that went to the starter as I described, and then just add in all new wiring between the batteries, starter, and alternator as I described? It seems to be the recommended way to setup an isolator, but I was thrown off by the cut off wire and the unused fusible link.

Thanks again!

 

[Don S]

Re: 1994 Volvo 7.4 GL Alternator Wiring

What are you calling a fusable link?
Typically, the main (orange) B+ terminal on the starter is wired directly to the A terminal of the isolators. Yes, it gets new wiring instead of cutting the oem harness apart. The main harness is just disconned from the starter and the alternator and a new wire run.

 

[jmsmieja]

Re: 1994 Volvo 7.4 GL Alternator Wiring

What are you calling a fusable link?

It's a guess on my part, but it looks like a fusible link used on cars. Not really sure of it's function on cars either, but someone with a lot of car experience mentioned it, and I found something that looked like it disconnected on my boat alternator. Could have been a car guy trying to fix something the wrong way, or just a splice on a wire that never got connected.

Wikipedia of fusible link:
Fusible link - Wikipedia, the free encyclopedia

Picture of a fusible link:


I don't have a picture of my boat showing what I'm talking about, but I can take one. Now that I think about it, I'm wondering if they just cut the wire where it came out of the engine harness, and then crimped a splice/butt connector on the end still attached to the alternator so that it couldn't touch ground. They then added a new wire off the POS terminal to go to the battery isolator. I plan to remove the stub wire anyway since we've determined it's not needed, fusible link or not.

 

[Don S]

Re: 1994 Volvo 7.4 GL Alternator Wiring

It's not a fusable link. What they usually are on the alternators are just short jumpers on the terminals that go to bullet connectors. They are also color coded for what goes to them.

 

[jmsmieja]

Re: 1994 Volvo 7.4 GL Alternator Wiring

There isn't supposed to be any fuses or circuit breakers

Don,

I got through the information you sent me. Thanks a ton. I'll apply it tomorrow to test the alternator.

The plot thickens a little. I was looking at the wiring diagram on page 3-18, and it shows a 50 amp circuit breaker between the alternator POS terminal and the starter. You had mentioned that there weren't supposed to be any fuses or circuit breakers. What are your thoughts on that? (See below)



The wiring in my boat looks like it has a 40 amp and 10 amp circuit breaker next to the battery selector. I'm not sure which is connected to what yet, but I'll have to look into that. Either way, no 50 amp in the circuit on my boat.

I believe the 20 amp fuse is still there and intact, but I'll have to pull it open to make sure.

 

[Don S]

Re: 1994 Volvo 7.4 GL Alternator Wiring

The 50a breaker is a red push button breaker. As I recall, they are located in the electrical box mounted on the front of the Starboard exhaust elbow.
The 20A fuse is located next to the ignition switch at the helm.

 

[jmsmieja]

Re: 1994 Volvo 7.4 GL Alternator Wiring

Don,

I tested the boat wiring per the instructions you sent me, and it all checked out okay. I did have some slightly reduced voltage on the excite and sense leads, but it was close to the lower limit.

I took the alternator off and brought it in for testing, and it tested bad. I had it rebuilt, put it back in and now have a functioning alternator. Thank you so much for your help! I really appreciate it.

I also looked into the battery isolator wiring some more, and it appears to be legit and working.