1970 Cutlass Electrical Problems - ClassicOldsmobile.com

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Old August 25th, 2010, 09:51 AM   #1
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1970 Cutlass Electrical Problems

I recently acquired a 1970 Cutlass. The car has an electrical problem that became known when the dual electric fans quit working and the engine overheated. I discovered the ďBatĒ wire leading to the Delco 10 SI alternator shorted itself against the engine block. The alternatorís R and F (1 and 2) terminals were spliced together and connected directly to the battery. I think the car has an original external voltage regulator that was bypassed when the Delco 10SI alternator was installed, but Iím not sure (see picture below). Also, a wire harness, leading from the back of the fuse block, runs along the left side of the engine compartment, it contains the wires for the head lamps, as well as some others. The harness has about six wires cut near the battery (located on the driver side). Of the wires that were cut, two red wires were spliced together and attached to the battery terminal. These wires appear to bring power to the fuse block. I imagine the cut wires may belong to the external voltage regulator, but Iím not sure. Can anyone tell me what the two red wires spliced together and attached to the battery are for? And what are the other wires for? (see picture of wires)

Also, when confronted with installing the new alternator, I need to decide how to hook up the two alternator terminals. I would like to run the #1 terminal wire through the original GEN light wire, but I donít know how to find the wire. In fact, the red GEN light illuminates when the key is switched on and the engine is not running and I have no idea where itís getting its power, or ground for that matter. Can anyone give me some insight on how the original electrical wiring was set up and what those cut wires are for?
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File Type: jpg Voltage Reg.jpg (33.4 KB, 290 views)
File Type: jpg wire harness.jpg (32.0 KB, 294 views)
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Old August 25th, 2010, 01:49 PM   #2
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Welcome to CO. If you don't get some replies to your question re-post in the electrical section tomorrow. Most replies here will be welcome aboard. For what it is worth, I think you are on the right track about the external regulator being removed from the circuit. A factory service manual would be invaluable to you in the future, they are found on ebay often enough.
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Old August 25th, 2010, 02:06 PM   #3
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Welcome aboard! I moved this to the electrical section, as this is a hacked mess that needs some cleanup for safety and reliability.

Guys - where is the horn relay / junction block on the 1970? I am thinking it was in that area and was removed here. The colors that were cut look to go to a horn relay.
In fact, i see a green wire that was cut... Does the horn work?
That nasty wirenut just has to go.......
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Old August 25th, 2010, 02:25 PM   #4
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1st question- did you do the fan install or was the car like that when you got it?

If it was like that already, you now officially own a POS (Previous Owner's Stamp).

Hate to sound discouraging in answer to your very first post, but this is heavily (and badly) modified wiring and may take us a while to sort out. Rob's good with electrical; he'll probably have you up and running soon.
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Old August 25th, 2010, 02:27 PM   #5
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I hope this helps somewhat. Ill try and get better pictures later today. The part circled is the horn relay and where i have an arrow pointed is where its actually supposed to be mounted onto the frame, but I need to fix some electrical myself and thats just how it fit. Notice all the tension on the one wire feeding to it :X This is on a 71 Cutlass Supreme

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Old August 25th, 2010, 05:25 PM   #6
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Thanks everyone for the replies.

, no the horn doesn't work and I think I now know why, and that yellow wirenut...it's already gone.

Rocketraider, no the fans were installed by the previous owner. I have since added a fan controller with with fuses for both fans and grounded them securely.

erke88, great picture, it answers a lot of questions. From what I've learned, GM used the horn relay as the main power distribution. It's also where the voltage sensing for the regulator was taken from. On my poor car, the relay was cut out and the wires that were left hanging were for the voltage regulator and power for the ignition/fuse block. Since I'll be using an internal voltage regulator, I think I'll purchase a conversion kit with a regulator jumper harness to replace the voltage regulator. I'll find a new horn relay and make the proper connections for the power and the alternator.

New question, in erke88's picture, there's a silver relay on the firewall next to the brake diaphram, what's that relay for?
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Old August 25th, 2010, 10:47 PM   #7
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If I were you I'd just get a new harness and call it a day. That is one hacked up mess for sure.
I replaced both my main engine harness and my front light harness last year and I can tell you it was WELL worth it.
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Old August 26th, 2010, 06:22 AM   #8
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On the 72 models, that relay is for the high speed heater / A/C fan setting.
The wiring on yours looks like it needs attention also. That is a high-current circuit and needs no bad splices or substandard wiring.
On your picture, its wiring looks hacked and there is a voltage regulator there. Odd place for the reg...

The horn relay can be had many places. It was a junction block, too.
Rockauto has the relays, as well as a variety of connectors, like for that heater fan relay, too.
Make sure there are no other crazy splices elsewhere down the line as well.
If you choose not to replace the whole harness, be sure to use appropriate terminals, solder the joints and use heat shrink on those joints.
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Old August 27th, 2010, 09:11 AM   #9
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Thanks again everyone. I purchased a new horn relay and traced all of the cut wires. Fortunately, they were all cut where the horn relay used to be. I soldered all of the terminals and shrink tubed them. The voltage regulator was moved, by the previous owner, to the right side of the firewall to accommodate a larger distributor (my guess anyway). With the new internal regulated alternator, I routed the field terminal to the GEN light, the voltage sensing terminal to the horn relay, and the BAT terminal directly to the battery. It all appears to be in accordance with the wire schematic from GM. I still need to place two fusible links, one for the horn relay to the main power, and one for the alternator "Bat" terminal. The wire harness is actually in good condition except for the horn relay portion. The horn and door buzzer work now, which is a plus. Thanks again everyone, your replies made a huge difference. In fact, many of my Google searches point to your forum for answers. Great Forum!
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