• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

more electrical questions

tarafied1

tarafied1

Well-Known Member
Okay, I still haven't solved the blinking instrument/tail light issue but I think Dave was on to something with the alternator.
Last weekend I was cruising around town, low speed just cruisin' when I came across some friends standing outside. I stopped to chat and left it idle while we gabbed thinkin I wouldn't be long. After a few minutes I realized I was going to be a while so I shut it off. After about 15 minutes or so I tried to start the car, the big 429 with 10.5:1 doesn't crank easy when it's hot but it wouldn't turn over hardly at all. I thought maybe the starter was hot so I waited a while longer. Still nothing. Long story short I needed a jump and it fired right up. Now I am thinking I don't have enough amps at idle to run everything and charge the battery. I have the bat in the trunk with a long cable so that doesn't help, also have a electric fan on a toggle switch with no relays. I have been researching on the web and that is a big no-no I guess. So I have read a lot on the web and see many posts saying different things. Some say 30-40 amp alt is good enough and some say you need a 65 to 100 amp! Right now the fan is tied directly to the hot side of the starter solinoid (pos bat side), would the fan (without a relay) be enough draw to cause these type of issues? and what size alt do you guys recomend? Also I guess I need to add a amp/volt gauge... When I put in the tach I tossed the amp gauge so I don't have a clue what the alt is doing.
 
30-40 amp alternators are fine for stock set-ups. Your radiator fan draws 10-20 amps if not more all by itself. Idling by itself doesn't do a whole lot for charging a battery or doing much more than running a stock setup. You need a higher output alternator, one that is capable of more current at curb idle speeds. Yes, your alternator and charging system isn't enough to fully charge a battery while idling for long periods of time. When you do that, you're draining the battery.
 
so do I need to go all the way to a 100 amp or would a a 65 work? Also would adding relays to the fan help or is that just for less shock to the system when you switch it on? I did add the relays to the headlights and they are brigher and I think I understand the purpose was not to lose voltage drop thru the old harness, but the fan is pretty much wired right to the battery.
The good news though, my dishwasher doesn't make suds!
 
A relay would be good, but a fuse would be better! A larger alternator doesn't hurt things (it simply can provide more current for other circuits), but it will only provide the amount of current needed. You can't "push" current to devices. I'd try the 65 amp version and if that doesn't help, then a 100 amp alternator would be next.

Can I interest you in an interest-free purchase of a good sudsing dishwasher?
 
While you're playing around with your electrical issues, now would be a great time to wire that electric fan into a thermostatically controlled sending unit. I use the Summit brand one that screws into the intake manifold water port and closes the electrical circuit at 190 degrees, thus energizing the fan. The sending unit is calibrated to "open" the circuit at 175 degrees thereby killing power to the fan power circuit. This thermostat switch ensures that the fan will only be energized when it's needed.

Electric fans can pull a LOT of amperage.... some in excess of 30 amps. Your OEM ALT can't keep up with the load and at low RPMS is causing the shutdown/intermittent operation of other systems.... like brake lights... and battery charging.

I'd move right to 100 Amps and be done with it.
 
Thanks, I like the thermostate idea. Can I still use my factory temp gauge with one of those?
I didn't realize the fan was such a big draw. Does Ford have a 100 amp alt or do I have to go with one of those Delco Remy alternators?
 
Can I still use my factory temp gauge with one of those?
Click to expand...

Does your intake manifold have more than one port drilled into a water jacket? Some intakes do, some don't. If the intake has only one port, there are ways around this. Some thermostat housings have a port on them. A kit can be bought that installs a port onto the lower radiator hose.... or even a heater hose. The extra port obstacle is easily overcome and yes, you'll be able to retain your factory water temp gauge/sending unit.


I didn't realize the fan was such a big draw. Does Ford have a 100 amp alt or do I have to go with one of those Delco Remy alternators?
Click to expand...

Depending on the quality of the fan motor, it can be a very BIG draw. Usually, the higher priced electric fans have a better motor that draws less amperage.

I'm not sure about OEM ALTs, but the PowerMaster ALT should have a model for your application.
 
You must log in or register to reply here.
Back
Top