I have been noticing that my alternator in the 69 hasn’t been pulling enough voltage when I have the headlights and heater blower on High. I think this has always been the case since since owning the 69 but honestly don’t remember last winter - had enough other issues at the time.

My initial thought was to add a smaller pulley - knowing that will make a difference at lower RPM, however with the heater on High and the headlights on it doesn't really matter what RPM I run. The voltage drops below 14v and sometimes even below 13 volts regardless.

Since I will be adding a control panel and a bunch of lights soon I figured it was time to trouble shoot the alternator. I know its a high power aftermarket job - but don’t know what amperage its supposed to put out assumming 120 or 150 - i need to dig out the paperwork.

In any case is there anything else i can check that would be killing the voltage? It seems to only happen with the heater on high - I did remove the stock heater controls and replaced it with a three way switch - could this causing a excess voltage draw?

I haven’t tried the winch, it would be the next big thing to draw power…

Thoughts?

I understand your resistance, but have you tried turning down your Taylor Swift?

Sounds like the voltage regulator is crapping out. What size is the power cable coming off the alternator?

Make sure you actually have a problem. The wiring, including the new aftermarket stuff, is thin. Your alternator may be putting out the proper voltage (at the alternator), but if your voltage is being measured back under the dash, you could be losing 0.5V - 1.5V along the way.

Voltage drop over a length of wire is proportional to the amperage flowing through it.

Voltage Drop = Amperage x Wire resistance

To determine, have someone hold the engine at 1200-1400 rpm. Measure the voltage at the dash(use the cig lighter outlet), and at the alternator. Then turn on your headlights and blower motor. Remeasure the dash and alternator voltages. I bet your see greater drop at the dash.

Yep, what he said ^^^^. I converted my pickup truck from the stock 2g fire hazard alternator to a 3g and my gauge on the dash didn't show any improvement, it still drops in the "normal" zone more than I thought it should. So I checked it at the battery and at the dash. Battery showed a nice even 14.2 volts regardless of loads and the dash read closer to 13.4 volts. Make sure you actually have a problem before you start creating one!

That's a perfect description of what happens to voltage when a belt slips. Startup drains the battery so you get a big load on the alternator as soon as it starts running. The load causes the belt to slip and the voltage to drop.

Does the voltage come back up once you get driving with the lights and blower motor on? With just swapping to the chevy blower motor in my bronco when you turn that sucker on the lights dim pretty good. But once the rpm come off idle they brighten up and the blower speeds up.

Is the wiring harness new or original ?

Do you have the head light relay harness on it ?

I found the paper work for the 1 wire alternator that the PO put in. Turns out it is a 95 amp aftermarket alternator however the specs say it doesn't turn on until 1200 RPM which would account for no charge until i rev the engine.

The stat sheet doesn't list anything below 1600 RPM and at that point its putting out 44 Amps - supposedly. I would suspect at Idle (600RPM) it can barely keep up with lights, heater, stereo etc.. and causing it to drop below 14v and causing all my lights to pulse and dim.

One thing of note that I had forgotten - i did replace the heater controls with a 3 way switch last last October. Not sure what kind of current that switch is supposed to see but I was in a pinch to fix it and found one at radio shack and stuck it in to have a heater. Iam ok with leaving the switch in there but I am suspecting I might need a high amp switch to handle the heater better? Might be part of my problem?

Here are some of the tests I did:

Battery has 12.7v unhooked
Headlights off, heater off I am getting 14.55v at the battery after i rev the engine to kick on the alternator - at idle
Headlights on, heater off iam getting 14.45v at the battery at idle
Headlights on, heater on low iam getting 14.35v at the battery at idle
headlights on, heater on high iam getting 12.75 - 14v at the battery at idle - lights dim and brighten, engine rpms are unsteady.

I have ordered a new 200 amp one wire Alternator as iam about to add a bunch more stuff to the electrical system and want to cover my bases - talked about adding a 2nd battery but that would mean moving both somwhere to the rear, not sure iam ready for that quite yet. I understand that I might have a rough time with one vbelt and trying to get it to stop slipping, but will try a smaller belt and do what I can to make it work.

iam also wondering if I should just stick a new heater control switch back into the dash as well. Thoughts?




I

Looks like i found my answer ;) Need to make sure i have a continuous 20amp rated switch...

http://classicbroncos.com/forums/showpo ... stcount=39