doghead starter relay modifcation

Credit goes to doghead for his instructions in thread "underdash starter relay" and the wiring picture as well.

This modification replaces the standard GM underdash starter relay, GM Part# 15591718 (which is prone to sticking), with a higher rated 200amp relay from Napa.

1. Buy Napa part# 7-01860-1 (SME line)
2. Disconnect your batteres
3. Remove diagnostic port under the dash and a couple screws which will release the mounting plate for which the relay is mounted to
4. Pull the mounting plate with relay down out of the dash so you can get to it, and remove the relay from the mount plate (IMG00541)
5. Mount the new Napa relay to the mounting plate. You can use one of the existing holes and then drill the other (IMG00542)
6. Cut off the old relay from the wiring as close as you can (IMG00543)
7. Put ring terminals on, and wire to the new relay according to doghead's picture (starterrelaywiring)
8. Tape everything up well with electrical tape so you don't have bare metal sticking out anywhere
9. Replace the mounting plate up into the dash, replace diagnostic port, and re-connect your batteries
10. Start truck with confidence

Edited to add: I'm no expert btw, I just did this off of doghead's instructions and he said he had started his about 100 times with no problems. I did it, started mine, and it works.

Proceed at your own risk.

I have been under the weather, sorry I have not done this thread myself(as I said I would). Thank you for compiling and posting the info. Others including Mistaken1, have also contributed to this(thanks). As I had said before. This relay is rated at 200 amp, I don't think we should ever see a failure with it.

The stock relay seems to work fine, unless something changes(starts going bad)in the system( such as, corrosion on the relay contacts, bad solenoid/contacts, bad suppressor, starter motor shorted/worn, low battery or bad battery- causing a high amp draw, or fuel and or Glow Plug issues). It seemed to be a week link that could cause collateral damage to the rest of the starting system.

If you were experiencing repeated failures of your original relay, I suggest you test and evaluate everything possible, before simply making this modification.

I just finished converting my M1009 and it works great. Very easy and now I do not have to deal with my relay frying my starter. The hardest part was drilling the whole in the dash. Very happy with the results! Thanks for the pics and instructions realm!

I did this mod tonight on my m1009 daily driver; it took maybe 30 minutes. Thanks for sharing the idea! I am going to do my other m1009 tomorrow.

I had mine get stuck on me last week. Lucky for me I had read about the relay's geting stuck on these fourms prior so when it happened I knew exactly what was happening. I poped the hood and disconected that battery as fast as I could, which again I was lucky to have my socket set sitting on the passenger seat. I used this modification and it has been working well so far. Thanks for the idea.

With a higher capacity start relay, there will be a healthy inductive "kick" when it's de-energized (start button released). To keep the start button contacts from arcing, install a diode as shown below. The diode may be an 1N4004 or equivalent.

cranetruck said:

With a higher capacity start relay, there will be a healthy inductive "kick" when it's de-energized (start button released). To keep the start button contacts from arcing, install a diode as shown below. The diode may be an 1N4004 or equivalent.

Click to expand...

Noob Question:

This diode would install between the purple/white lug and the black ground on the starter relay?

Also, would this diode be needed if using a 12v system?

Yes, the diode goes across the wires you described, the black ground and the 12v purple with white stripe.

Ken_86gt said:

Yes, the diode goes across the wires you described, the black ground and the 12v purple with white stripe.

Click to expand...

Edit, I see, you are protecting the ignition switch in the column.

I know it is not absolutely neccasary but, I have extra diodes laying around from another addiction (pinball) and want to put one in when I replace my starter relay. Does the orientation of the diode matter? Ie.. should the banded end face the ground wire (black) or the purple and white wire? or does it not matter?

Thanks,

Bill

The orientation does matter, in this case you want to put the end with the stripe towards purple and white wire. If you get it wrong it will burn up.

February 22nd, 2010.

Might I suggest the use of Liquid Electrical Tape instead of wrapping the resultant mod in regular electrical tape? The item should be available at Home Depot, Lowe's or your local electrican's supply shop, and might make a neater and more reliable job as it should be rated for 600V. Just a suggestion. And thanks again, Doghead, I don't even own a CUCV and I am wondering if M35A2's are also liable to this malfunction, or is it primarily a GM thing?

Cheers,

Kyle F. McGrogan

Just the General Motors CUCVs, have this issue.

Is there any problem with using the cylindrical glow plug relay in place of the original starter relay?

the cylindrical glow plug relay

Click to expand...

Depends what relay you are planning to use? (I have no idea what part you want to use instead) Do you have extras? Why not just use what's explained in this thread? You can use or do anything you like. Your results may vary......

I have a spare relay from the glow plug system. The round one that is between the resistor and the glow plugs. Did not know if it would work.

Yes, that one should work fine(kinda loud). It's kinda big, to mount in the same location.




The relay I selected in the modification posted above, was the best choice, considering size, position of mounting, load, availability, quality and price. A lot of thought went into this, and to my knowledge, it has been 100% effective in eliminating the relay failure/starter run-on issue.

fwiw, some relays are position sensitive, if you don't know the design specifics of a part, don't use it!

FYI I found these@ Beco elect. Co. inc 864 242 6480 for 12.36

I'll be performing this mod this weekend, as my existing relay has gone bad. One question,, which looks to have already been addressed,, but i'd like to be absolutely sure i understand correctly----- is the diode just spliced inline into the existing ground wire...?

Hundreds of starts, no diode, no problems.