OT: older truck alternators

M Puller in WI · Oct 14, 2009

last summer i put a motor out of an "86 chevy scottsdale 20 into my "91 chevy 1500. i got rid of all the A/C pump and that since it didnt work anyway so now its got the old 2 belt system. my problem: the alternator out of the 91 motor will not fiton the older style brackets so i have to use the alternator on the "86 motor. the plug is different. the plug for the alternator on the 86 has 2 prongs with 2 wires going to it. my 91 had 1 wire with 1 prong. so on the 86 where do the 2 wires go? one is white and 1 is red and the red is bigger then the white.
sorry if this gets confusing but i want to convert my '91 to the older style plug. im currently running a 1 wire alternator but that sucks when driving at night. when ya let off the gas the lights get dimmer.
so my question: where do the 2 wires on the 86 go from the alternator? there is a plug with 2 prongs on it. 1 white and 1 red.
thanks in advance!!!
M puller

TractormanNC · Oct 14, 2009

On the 86, the red wire is always hot 12 volts.
The white one comes from the load side of the ignition switch thru the "gen" or "bat" idiot light.

Sorry, can't help you on the 91. Too new for an old fart like me.

dawsonn · Oct 14, 2009

If you look On the 86 alternator the number 1 wire comes from the key or a power source and the number 2 is the since wire which is hot all the time. with the one wire alternator those wire can be used for turning on dash board lights. The reason your lights dim I would think is because the pulley on the one wire alternator is larger than the 91 alternator. Most of the time on the one belt alternator the pulleys are much smaller and so the rpm is much faster, if this is the case you could get a smaller pulley for the 86 alternator, hope this helps.

M Puller in WI · Oct 14, 2009

so now with putting that that older style alternator in my 91, would i hook up the white wire to the exhisting wire that goes to the dummy light? then what does the red wire go to? or do i even need to worry about making the plug off the 86 work on my 91? sorry i didnt clear that up i have a 1 wire alternator off something else on there now
thanks
M Puller

M Puller in WI · Oct 14, 2009

sorry i messed up again. there are 3 wires. 1 that is held on the terminal on the alternator by a nut( the wire that comes from the battery) and then the red a white wires on the plug.
sorry to confuse you guys!
M Puller

Bob · Oct 15, 2009

Connect the #2 "Voltage sense" wire on the older alternator to it's large output stud along with the heavy charging wire

Connect the BROWN wire that used to connect to the little plug on the '91's alternator to the #1 "switched excite" terminal on the replacement '86 alternator. That's it. All done, all's well.

Duner Wi · Oct 15, 2009

You can purchase at flaps a conversion plug for newer engine/alt and older harness or the other way around, old engine/alt. and newer harness. The people who do engine conversions use them.

M Puller in WI · Oct 15, 2009

thanks a lot Bob! i did that and it works like it should!
Thanks a lot!
M puller

OT: older truck alternators

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