M38A1 Battery Ground Strap Location

madmike · Post by **madmike** » Sat Sep 03, 2011 5:54 pm

Moving forward on my project, I noticed that in a couple pictures of restored jeep engines, and in the manual, the ground strap on an early A1 is bolted to the rear of the motor mount and is routed up behind the front engine plate and then I believe bolted to the generator bracket bolt. Mine, when I got it was routed from the front motor mount bolt, up the front of the engine plate and to the bracket bolt.

Which is correct? Does it really matter? It would seem to be more out of sight routing it behind the generator but difficult to get to if you needed to service it, clean the grounds, etc. Would appreciate y'all taking a look how yours is routed. I have a 1961 vintage A1.

Also, one end of the strap is round and one squared off. I'd be guessing at the correct orientation for this but I'm thinking the round end would be at the motor mount.

53a1 · Post by **53a1** » Sat Sep 03, 2011 7:19 pm

Even if it's not original I would go with the three hole strap. This ensures your generator is well grounded. Here's a pic of how I routed mine. Bought mine is from MWM and it fit perfect as usual. Be sure to use the external spline lock washers to dig into the metal for a good ground. On all fasteners for the strap I use electircal contact lubricant (Home Depot) to prevent corrosion. I also spray it on the strap itself. It's good stuff because it dries and seals the metal from corrosion but still remains conductive.

http://www.willysmjeeps.com/v2/modules. ... c&start=75

madmike · Post by **madmike** » Sun Sep 04, 2011 1:38 pm

Thanks for the reply and after seeing your routing of the strap, that is what I will do as well. I looked thru your posts and pictures and would to know where you got the Lucas zinc break in additive. Is that readily available? I have a NAPA nearby.

madmike · Post by **madmike** » Sun Sep 04, 2011 5:58 pm

Well...now I have to update my last post because I cannot route the same way 53A1 did his. My ground strap, also from Midwest, fits if I use the front bolt of the motor mount, then to a bolt and nut on the engine plate near the lower generator mount, and then behind the mounting bolt for the generator upper support and adjusting arm. If I try using the rear motor mount bolt, none of the other holes in the strap line up. So there must be different ground straps for early and late A1's. If not, I'm once again baffled as to where the strap would mount, other than what I have done.

I have been threatening to try posting a picture(s) so I will try to do that after I convince my wife to snap some more photos. Want to touch up the paint first though.

Post by **wesk** » Sun Sep 04, 2011 8:55 pm

The strap on the right front engine mount is the engine to frame bonding strap and is fastened from the rear engine mount pad bolt to the generator mounting bolt for the 2 hole strap and then on to the small free hole in the front plate just inboard and above the generator mounting hole. There is a variation here because the short two hole strap is used from MD10001 (1952) thru MD83475 (APR 1955) and the 3 hole strap is used from MD83476 and on.

There is no need or reason to connect an additional jumper to the generator case since it is already grounded to the regulator and at the regulator is then grounded to the frame. The harness cable housing that runs from the generator to the regulator is braided stainless steel and provides the generator ground. It is more important that the generator's ground potential matches the regulator's then for the generator to be grounded to the engine.

53a1 · Post by **53a1** » Sun Sep 04, 2011 9:17 pm

Napa can order you the Lucas Break-In with Zink but don't overdue it. In this case a little is better than a lot. Wes is correct but extra grounding never hurts. If yours doesn't fit just skip the Gen hookup and mount the end to the engine mount plate but if you got it from MWM it should fit. I can take another photo if it would help.

I wasn't sure how to route mine so keep investigating if you want it 100% original.

madmike · Post by **madmike** » Mon Sep 05, 2011 4:10 pm

I have the later three hole strap Wes mentioned and the only way I make it match the holes he referred is to use the front mount pad bolt. The strap is predrilled (all three holes) and the hole at the extreme other end is much larger to accommodate the larger bolt on the generator arm mounting. The strap also is squared off at that end and rounded at the pad end. My original strap was eaten away at the large end and I could not determine the original shape.

I painted the strap after installation and ensuring I had a clean metal to metal ground. I did this because the USMC jeeps appear to have just about everything painted over with their green, not because I knew what I was doing. Just seemed like it would be painted just before adding the generator and starter.

I will check with Napa on the additive and I already have the 15/40 since I own a Dodge diesel as well. New rings and bearings in this engine and I want to break it in right.

Post by **wesk** » Mon Sep 05, 2011 5:18 pm

There is no documented source of info on which bolts were used with the three hole cable so I would go in your directions and if it fits on the front bolt then that must be where it goes.

For the early 2 hole strap the illustration Fig 54 in TM 9-8014 on page 126 and Fig 91 in TM 9-8014 page 188 should suffice for the data needed.

Lf you look closely at the Fig 91 you'll see the inboard end of the cable though not visible certainly looks like it is bolted to that small bolt just inboard of the generator pivot bolt. That along with the two 5/16" star washers called out in the ORD 9 convinces me that at least on the early model A1's the ground strap did not fasten to the generator pivot bolt.