Verify it's the alternator
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Freshman User
Joined: Feb 2005
Posts: 29
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Verify it's the alternator
Everytime I use my heater with the defroster (a/c compressor runs) and the radio is on and the headlights, my volts drop so low that the truck wants to die, even registers low when the head lights and radio is on but not much. COuld a diod be bad in the alt.
Also what controls the tach in the dash (my rpm guage) it also bounces all over the place when I either rev the motor or small changes in the throttle.?
89 Bronco 5.8L C-6 tanny 129,000 miles and everything is original.
Also what controls the tach in the dash (my rpm guage) it also bounces all over the place when I either rev the motor or small changes in the throttle.?
89 Bronco 5.8L C-6 tanny 129,000 miles and everything is original.
Junior User
Joined: Apr 2005
Posts: 98
Likes: 0
The Tach is electronic and gets a 12v supply to run it as well as a reference pulse from the TFI module. If your voltage is low or worse your electrical system is noisy (AC on the 12v line from a bad rectifier diode), it will cause the tach to go crazy. Best test is to charge up the battery, disconnect the alternator output lead and start the truck up and run it on the battery, see if it cures your tach issue. I don't know what your stock alternator size is, but a lot of older broncos only came with a 65a unit. You probably could pick up a 130a unit fairly cheap, I have a 220A alternator in mine, but be careful, the larger size alternator you get, the faster you will have to turn it to get output (usually accomplished with smaller alternator pulleys), and the worse it will perform at idle (680rpm), I had to raise my broncos idle to 990 rpm for good output at idle, otherwise everytime I stopped at a light, everything would dim.
Elder User
Joined: Jan 2005
Posts: 656
Likes: 1
From: Houston
I had the same problem. One thing I found that really made my alt work better is when I discovered the ground wires that connect the engine to the frame. When I moved them around and got a good ground on them my alt performed much stronger. Now my alt has finaly died. So last month I bought a new one. (Stock) now I have more juice reading than I could have ever thought I could get.
