Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: GM 7-Pin Large Cap HEI?

  1. #1

    Default GM 7-Pin Large Cap HEI?

    I see an ignition adapter for the small cap computer controlled HEI but not the large, any reason?

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,734

    Default

    The large cap computer controlled HEI distributor just isn't as popular.
    However, you should be able to obtain the pigtail repair connector(s) at an auto parts store.

    The 1981 & later, large cap EST ECU timing controlled (OEM), can be used.
    They're the same ignition module logic as the small cap computer controlled units.
    Although, the coil-in-cap model distributors are not preferred for high performance use.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3

    Default

    Thanks, I really don't have much of a choice. I'm running a Pontiac V8, I don't feel like spending huge amounts of money on an aftermarket MSD or equivalent so luckily I have my old C950 Commander harness I can cut the pigtail off of.

  4. #4

    Default

    Quick question, I bought the small cap HEI adapter harness to splice into instead of the main harness.
    Do I just splice the wires color to color or do you have a link to a wiring diagram/pin-out for the two different distributor wiring?

  5. #5
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,734

    Default

    Quote Originally Posted by Chuckles View Post
    Quick question...I bought the small cap HEI adapter harness to splice into, instead of the main harness.
    That was a smart move...do the splicing/wiring on the separate adapter harness.
    If not using a small cap GM HEI distributor, the 558-304 ignition adapter harness can still be utilized by cutting off the small connector,
    and wire your distributor type according to the wiring diagrams. This is outlined in the Holley EFI Wiring Manual (center of page 15):
    http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual)

    Do I just splice the wires color to color or do you have a link to a wiring diagram/pin-out for the two different distributor wiring?
    The 8-pin HEI module is essentially the same as the 7-pin HEI module, except for the additional ground wire (G).
    According to the second link below, the 7-pin and 8-pin HEI modules are wired the same as color coded.

    For reference:
    http://www.megasquirt.info/HEIgn.htm (GM HEI 4 & 7-pin modules)
    http://www.msextra.com/doc/ms2extra/MS2-Extra_HEI.htm (GM HEI - all modules)
    https://www.holley.com/document/tech...y_r10149-7.pdf (Commander 950 Manual - page 104)
    http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual - page 13)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  6. #6

    Default

    OK, really weird. I disconnected the coil RPM signal wire coming off my tach wire to install my ignition adapter harness to run my computer controlled HEI and now it has no RPM signal. Am I correct that I should only have to plug in the harness connector to receive an RPM signal from the distributor?

  7. #7
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,734

    Default

    Quote Originally Posted by Chuckles View Post
    Am I correct that I should only have to plug in the harness connector to receive an RPM signal from the distributor?
    Did you have an RPM signal beforehand?
    Is there an RPM signal with the TACH wire reconnected?
    Is there switched +12V when you turn the key?
    Is the ignition module/distributor still grounded?
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  8. #8

    Default

    Quote Originally Posted by Danny Cabral View Post
    Did you have an RPM signal beforehand?
    Is there an RPM signal with the TACH wire reconnected?
    Is there switched +12V when you turn the key?
    Is the ignition module/distributor still grounded?
    Yes. RPM Signal with TACH wire reconnected. +12V present and distributor/module is grounded.

  9. #9
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,734

    Default

    Quote Originally Posted by Chuckles View Post
    Yes. RPM Signal with TACH wire reconnected. +12V present and distributor/module is grounded.
    I'd check for a bad connection or a broken wire.
    You didn't short anything while working around the module or pick-up coil?
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  10. #10

    Default

    I Ohm tested the adapter harness with my meter. Connection is fine. And I can reconnect tach wire and car will run.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
About us
Holley has been the undisputed leader in fuel systems for over 100 years. Holley carburetors have powered every NASCAR® Sprint® Cup team and nearly every NHRA® Pro–Stock champion for four decades. Now, Holley EFI is dominating the performance world as well as our products for GM's LS engine. Holley's products also include performance fuel pumps, intake manifolds & engine dress–up products for street performance, race and marine applications. As a single solution, or partnered with products from other Holley companies - Hooker Headers, Flowtech Headers, NOS Nitrous, Weiand, Earl's Performance Plumbing, or Diablosport - Holley products can give you the edge you need over the competition.
Join us