illuminations

[timmytim]

While idling my headlights dim. I think the alt is weak,what do you think

[Dragon]

With stock voltage regulator and 65A Alternator the alternator does not run the lights it barely charges the battery so the lights dim. It needs about 1500 rpm to produce enough current to do both. With my electronic regulator my engine's mild miss makes my headlights pulse.

[timmytim]

I have not had it tested but I dout this alternator has 65 amps.A stock 1970 f100 came with 65 amps? I figured the most would be 45 amps

[Dragon]

Most trucks after 67 had 65A alternators. Most not all. I never bought one or worked on one at Ford that had less than 65A.

[timmytim]

been looking around autozone has one thats 61amps and advanced has one that is 65amps

[Dragon]

Funny where did the 61 come from. 65A, Ford never had a 61 amp. Let's see where autozone has repeatedly got things wrong. 2 hole starter for a FE. Autolite carb for 390 2V was a 352 carb in the box.

We had 42A, 55A and 65A rare 90A.

The farther these people get from the reality of the original trucks the more they will get things wrong.
From O'reilly they list this
Motorcraft - Alternator
Part Number: GL-198ARM
Line: MOT
38, 42, 55, 61 Amp
One alternator cannot be different currents.

But above that they get it right for trucks 42A and 65A
Different amperages as not all trucks came with radios whether you had marker lights or not and so on.

[SteveC]

My 67 has a 38a alternator. Still had the sticker that said motorcraft 38a on it. Least it did till I power washed my motor and engine compartment when I did my 4x4 swap. I'm planning on doing a 3g swap before to long though cause with the flat bed I added on there is gonna be added flood lights added to the headache rack

[fordman]

i think they came in 38 45 55 and 65. the wiring may be different for the 65 amp.

[Dragon]

Wiring is the same except for the fusible links

[timmytim]

if i have a 38a can i just install a 65am with not havin to do any changes?

[fordman]

im not sure. i looked at the 70 master diagram. http://www.fordification.com/tech/wirin ... master.jpg and the 68 65 amp diagram. http://www.fordification.com/tech/wiring/68-07.jpg but i didnt look real hard and trace all the wires. it does seem the 68 uses a field relay in the wiring seperatly. i am going to guess the field relay is either intergrated or not used with other alternators. really i cant help on this i dont knwo enough abotu it to say yes or no. but i thought i would post the difference i found looking at the two diagrams.

[Dragon]

The field relay is in the regulator of all F100-F350 Alternator systems. For our trucks If you find 2 3 wire harnesses going over to the regulator then the harness has been swapped out.

Your dimness won't go away like you think by switching the early alternators. They all at an idle don't put out 14 volts but by 2000 they do and even by 1400 rpm most will so when the lights are on the battery is really running the lights at an idle. Don't believe me let your truck idle for a few hours with the light on and watch your battery get so weak that the engine dies. We did this one night in a field with a brand new 69 F100 with 65A alternator while I was repairing a diesel for the Hay hauling semi group. After about 4 hours the engine started running rough so I ran over to it and revved it up. The lights got way brighter so I let it idle and get sick and read the bat voltage we were down at 9.7 volts. I set the idle up to 1500 and we went back to work. The battery was getting 14. volts after I raised the idle.

Look into the small case 1G 100A alternator it puts out 13.5v at an idle at about 18 amps.

[fordman]

ok so he can probably swap it in and it shouldnt be a problem then.

[Dragon]

Yes one harness all alternators.