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Hello, y'all!

I'm in need of a 12 volt wirng diagram for a M37 / M43. My vehicle was converted to 12V at some point, and everybody since then has made some sort of modification to it. I'm just trying to get my rig running. Replaced the exhaust systme, reinstalled the battery, hooked up the charger (just in case), turned ignition "On" and hit the starter switch. Starter spun for a coupla' trys with the engine not wanting to catch, then nothing. With proper (12V) voltage, hit the stater switch and there is a low hum from somewhere (can't localize it) but no starter turn.

I'll toss this in... would I be better off in just going back to 24V than trying to figure out the monkey mess I have now? I have two stock type wiring looms, but would need new / correct starter, generator / alternator, etc.

Please help me G741 people, you're my only hope!

Russ
Proud son of Rose and Wes

The charging system should be the only part that would vary from the 24v wiring diagram. And that modification would depend on the type of alternator. Other than that the standard wiring harnesses should work. (you may have to cut off the douglas or packard end terminals to connect to your 12v guages/sening units. If it is a real hack job it would take less time to install the correct harnesses than to figure out the existing rats nest....

This will be your biggest challenge, Russ.

Mine is 12v too, and had a birdnest for wiring. I couldn't afford converting everything back to 24v so I ended up installing a Painless Performance harness. It wasn't entirely painless and this was my first attempt (I still have to figure out the headlight switch configuration-just haven't had the time, and the civvy switch and all other electricals are working).

Anyway, just to get yours running you may need to detach the birds nest and just run a good set of "have to have" wires:
Postive and negative cables, a good block to ground wire, a hot wire to the coil, and a hot wire to power the starter solenoid. If you don't have or have never used a multimeter, you'll need one and learn how to use it or you'll never get the demons out of the wiring.
Good luck and don't give up!
Gary

If the engine cranks, all you should need is 12V to the + on the coil
and points grounding the - side of the coil out ( and a good capacitor)
As long as your cap, wires and rotor are ok, she should fire up.
J.B.

I just reread the first post. Does it sound like it's spinning bur not engaging? Check all the BIG wire connections and have somebody give the starter a sharp wrap with a persuader <sp?> . Or does it clunk and
hum without a spinning saound.
Geez what a goofy post I'm doing. I have a hard enough time making these sounds with my lips and mouth, I never had to do it with text before.
J.B. Ha Ha

Hiya, J.B.!

Thanx for the reply. The starter had turned the engine several times. Third time I tried I got bumpkiss. Got out the multimeter and did some checking... everything was getting proper voltage to it and thru it. I "think" the starter has pooped out and am gonna take it by Pep boys to get them to check it. Removed it and I hope its bad... a good 1/8" to 3/16" is missing off the end of each of the starter teeth. D'Oh!

My wiring is also seriously messed up tho'. It has had the On / Off switch replaced with a toggle switch, it only controls a electric fuel pump (for priming?). It also has a auto-type lockable ignition switch wired in. The starter is actuated by a push button switch that someone thoughtfully put a hole in the dash for. I had not realized that the large plunger type thing was actually for the stock starter.

Russ

Sounds like your starter is working fine. However, with that much off of the teeth, it's just spinning, and not spinning the flywheel at all! Hopefully that will get you fixed up.

Hey Cal_Gary, Where do you get a "PAINLESS PEREFORMANCE harness ? I have a 12 volt system too, and presently am using commercial #THHN 12 gauge stranded wire to make my own miserable harness; which works, but scares everyone i show it too, including myself !

Hi Peter,
I got the GM non-keyed 10104 kit. You'll also need about three packs of their Power Braid to insulate the lines. Auto Zone is a Painless Performance dealer and can order whatever Painless Performance stuff you need. Do a 'net search to see who else in your area deals with Painless Performance products.

I will also tell you that it isn't entirely "painless" to install one of these in an M, but it's much easier if you have and know how to use a multimeter. Painless' tech support guys are great too-they know the harnesses like the back of their hands. The only part I have not yet completed is the headlight switch, but I used a Painless GM-style switch for the short term and all of my service-drive electricals work-lights, gauges, switches, etc.
Less expensive than going with a complete new M harness set, too.
Gary

Thank You Cal_Gary...I do have those parts stores near me too. Well I guess I have a summer project to look forward too.

The most important thing is to read through the instructions several times before you begin, and don't rush through the install. When you first uncoil the huge bundle of wire the fear factor appears for a moment. Once you realize there are 4 different groups you can do one group at a time. My first group was the engine group, as I needed to ensure it would run again once I began, and it wasn't too difficult. The wires are clearly labeled where they go, with plenty of extra runs for a heater, electric fuel pump, etc. I'll gladly offer guidance should you decide to tackle this-also note that I did not wire the b/o lights as I run gammagoat taillights and have no b/o drive light at this time. I should send Robi some pictures to post....
Gary