hi folks,
i own a 1990 accord 4 door. the alternator is overcharging. when @ idle she's fine but when i drive she overcharges. is there a way that i can go to my local radio shack and purchase a resistor and install it on my car so that it can control the voltage. if it's only gonna cost me a couple of bucks and 5 min to install, i would like that idea better than to take out the alternator.
can that be done?
thnx guys

How do you know it is overcharging? Is it boiling the water out of the battery? Is the voltage out of the alternator higher then 15 volts with everything connected? How do you know?

No, you can't do that. With the amps involved, the resistor would get quite hot, most likely requiring a heat sink.

I think the car's powertrain computer controls the regulator on yours, if the wire is disconnected or burnt, there is no regulator control of output. Check before popping for a new alternator....I seem to remember this being a fairly common problem on that era of Accord, but my mind is slipping too, so who knows?

I'm guessing that it's overcharging by this method:
Put multimeter on the battery: engine off 12v
engine idle 12v to 14v
rev engine 15v to 16v
When i start my car everything is fine no alt/batt light. When i drive to work for 1 hour everyday, at the 40 min drive time alt/batt light comes on. To remove the light all i do is turn on the rear defrost and it goes away but if i drive like that for at least another hour then the light will come on. My guess is that it can't be undercharging cause that would mean under 11v while motor running. As far as jeffcoslacker goes where do i find this wire for the powertrain computer. I would like to check that before i pop in a used alternator in my oldie. Also the idea of the resistor, couldn't i make a mod and put a heatsink on it.

I believe any automotive store will check your alternator for free.
The probems you decsribed point to a bad alternator. But unfortunately you will not be able to fix it with the just a resistor. Most likely you voltage regulator is dying. As far as I know it is located inside the alternator. Your car's eletrical system needs that even 14.6 voltage flow.
Good luck,

Sam

ok,
when i remove my alternator can i replace just the voltage regulator?

ok,
when i remove my alternator can i replace just the voltage regulator?
I have not taken Honda's alternators apart. I have taken apart Subaru's alternator. The regualator was soldered inside the body of the alternator to about 15-20 conatcts. I was going to do this but with the price of the regulator of 40 dollars I did not dare. I just bought a new (remanufactured) alternator.

Sam

http://www.t24ever.com/images/obd1%20ecu%20plugs.gif

KEY:
(voltage values measured in DC Volts unless otherwise specified)
V = Volts
Wht = White
Blk = Black
Grn = Green
Yel = Yellow
Brn = Brown
Blu = Blue
Org = Orange

KOEO = Key On Engine Off
KOER = Key On Engine Running

A, B, D= Slot. Numbers are read up and down from left to right, not straight across (see diagram at end).

A1-INJ1 INJECTOR#1 Brown, Battery Voltage with KOEO
A2-INJ4 INJECTOR#4 Yellow, Battery Voltage with KOEO
A3-INJ2 INJECTOR#2 Red, Battery Voltage with KOEO
A4-VTS VTEC solenoid GRN/YEL, n/a
A5-INJ3 INJECTOR#3 Blue, Battery Voltage with KOEO
A6-PO2SHTC O2 sensor heating element Org/Wht, Battery Voltage with KOEO
A7-FLR1 fuel pump Grn/BLK, Battery Voltage with KOEO
A8-empty A7 and A8 have the same circurt, so they can be the same
A9-IACV IAC valve Blk/Blu, About 10v KOEO on Warm engine
A10-empty
A11-EGR Control Solenoid Valve (if the ECU has it) Red, n/a
A12-FANC engine coolant temp switch Blu/red, n/a
A13-MIL MIL (check engine light) Blu/wht, n/a
A14-empty
A15-ACC (a/c compressor clutch) Red/Blu, n/a
A16-ALT C alternator Wht/Grn, n/a
A17-IAB IAB Solenoid Pink, n/a
A18-Org/Red, Transmission Control Module (A/T), n/a
A19-White, Intake control solenoid, Battery Voltage with KOEO
A20-PCS EVAP purge control solenoid Red/Grn, n/a
A21-ICM Yel/Grn, Ignition Control Module output signal, About 10V KOEO
A22-Igniter, same as A21
A23-PG1 ground Black, Power ground, less than 1V
A24-PG2 ground same as A23
A25-IGP2 to main relay and to ground Yel/blk, Battery positive from Main relay, Battery Voltage with KOEO
A26-LG1 gound Blk/red, less than 1V

B1-IGP2 to pin A25 Yel/Blk, Battery positive from Main relay, Battery Voltage with KOEO
B2-LG2 ground to shields for CYP & TDC Brown/Blk, <1V
B3-Orange, upshift/downshift comparative input, n/a
B4-Pink, upshift/downshift comparative input, n/a
B5-ACS a/c switch Blu/Blk, a/c input, ~5V with KOEO & A/C off; <1V KOER with A/C & blower on
B6-empty
B7-Light green, Park/Neutral switch (A/T), <1V in Park or Neutral with KOEO; 5V in Park or neutral with KOER; Battery voltage in all other positions
B8-PSPSW PSP switch Red/Green, Power steering oil pressure switch, 0V KOEO; Battery Voltage KOER While slowly turning steering wheel
B9-STARTER SIGNAL starter signal Blue/red, Battery Voltage in the START position (clutch depressed on M/T models)
B10-VSS vehicle speed sensor Orange, Pulses 0-12V while turning the left front wheel
B11-CYP P CYP(#1 piston position) -P Orange, CYP sensor input, n/a
B12-CYP M CYP -M White, CYP sensor signal, n/a
B13-TDC P TDC(top dead ceter) -P Org/Blue, TDC sensor input, n/a
B14-TDC M TDC -M Wht/Blue, TDC sensor signal, n/a
B15-CKP P CKP(crank position) -P Blu/Green, CKP Sensor input, n/a
B16-CKP M CKP -M Blu/yel, CKP Sensor signal, n/a

D1-VBU Back Up Power Wht/Yel, Battery positive From battery through Fuse Box, Battery Voltage at ALL times
D2-BKSW brake switch Grn/wht, Battery voltage at all times
D3-KS Knock Sensor Red/Blue, n/a
D4-SCS service check connector Brown/Wht, ~5V (M/T); ~11V (A/T)
D5-empty
D6-VTM VTEC pressure switch Light Blue, n/a
D7-TXD/RXD (data link connector) Light Green/Red, n/a
D8-empty
D9-ALT F alternator Wht/Red, Alternator Charging Signal, ~4.5V KOEO; Decreases under Electrical load (Headlights & rear defogger on) At warm idle
D10-ELD electric load detector input Grn/Blk, n/a
D11-TPS (throttle position sensor) Signal Red/Blk, ~0.5V KOEO with throttle fully closed; ~4.5V KOEO with throttle fully open
D12-Wht/Blk, EGR Valve Lift sensor, ~1.2V KOEO
D13-ECT (engine coolant temp) sensor input Yel/Blu, ~5V KOEO (varies with temperature)
D14-PHO2S O2 sensor White, heated 02 sensor Signal, 0.4-0.5V when ignition is turned on; drops to less than 0.1V within 2 minutes
D15-IAT Intake Air Temperature sensor signal Red/Yel, .05-4.5V KOEO(Varies with temperature)
D16-VREF (no info)
D17-MAP Map Signal Wht/Blu, ~3V KOEO (Varies with Temperature)
D18-Light Green/Blk, Transmission Control Module (A/T Only), n/a
D19-Red/Wht, Reference Voltage, ~5V KOEO
D20-Yel/Wht, Reference Voltage, ~5V KOEO
D21-Blue/Wht, Sensor ground, <1V
D22-Green/Wht, Sensor ground, <1V


__________________



I think this is yours....if so, the signal at D9 is the one we are concerned with...check that the wire is continuous to the alternator, and the voltage is as stated...

If this doesn't look like yours, you'll have to find the correct one for your car.

ok,
when i remove my alternator can i replace just the voltage regulator?

I bet you can. Check Honda part list, the regulator assy is replacable. But the price for new one is not cheap ($150 -- $200). You can try junkyards, the whole alternator may only cost $20.

And, by the way, don't do the resistor thing, it's not gonna work.